WO2025083675A9

WO2025083675A9 - An insufflator, a method for operating an insufflator for insufflating a cavity, and a method for insufflating a cavity

Info

Publication number: WO2025083675A9
Application number: PCT/IE2024/000012
Authority: WO
Inventors: John O'dea
Original assignee: Palliare Ltd
Current assignee: Palliare Ltd
Priority date: 2023-10-20
Filing date: 2024-10-21
Publication date: 2025-08-28
Anticipated expiration: 2026-04-20
Also published as: WO2025083675A3; WO2025083675A2

Abstract

An insufflator (1) for insufflating a peritoneal cavity (2) of a subject (3) comprises a microprocessor (25) operating a flow controller (19) in response to a signal read from a pressure sensor (29) indicative of cavity pressure for insufflating the cavity at a target pressure value. The microprocessor (25) reads a signal from a pressure sensor (37) indicative of the peak airway pressure of a subject, and operates the flow controller (19) and/or a venting valve (33) to reduce the cavity pressure to prevent the peak airway pressure of the subject exceeding a maximum safe peak airway pressure value. The heart rate of the subject (3) is also monitored, and insufflating of the cavity (2) is terminated on the heart rate of the subject falling below a predefined minimum heart rate value. The insufflator (1) may also be configured to monitor the depth of anaesthesia of a subject by monitoring an alternating component of cavity pressure induced in the cavity pressure by ventilating of and/or natural breathing of the subject.

Description

An insufflator, a method for operating an insufflator for insufflating a cavity, and a method for insufflating a cavity

The present invention relates to an insufflator for insufflating a cavity in the body of a human or animal subject, and in particular, though not limited to an insufflator for insufflating the peritoneal cavity in the body of a human or animal subject or a cavity, vessel or organ located in the peritoneal cavity. The invention also relates to a method for operating the insufflator to insufflate a cavity in the body of a human or animal subject, and in particular, though not limited to a method for operating an insufflator for insufflating the peritoneal cavity or a cavity, vessel or organ located in the peritoneal cavity, the invention also relates to a method for insufflating a cavity in the body of a human or animal subject, and in particular,' for insufflating the peritoneal cavity or a cavity, vessel or organ located in the peritoneal cavity.

During a minimally invasive investigative or surgical procedure in the peritoneal cavity of a human or animal subject, the peritoneal cavity of the subject is insufflated. A number of complications may arise during the period while the cavity is insufflated. For example, in the initial stage of insufflating of the cavity, when the cavity is being insufflated to bring the cavity pressure up to a target pressure value, it is essential that the rate at which the cavity is being insufflated should be controlled. It has been found that insufflating the peritoneal cavity at a relatively high rate may cause bradycardia (a slow heart rate).

It has been found that rapid insufflation of the peritoneal cavity may result in a sudden increase in intraperitoneal pressure, which may lead to reflex-mediated cardiac inhibition through the vagus nerve. This is known as the Bezold-Jarisch reflex, and can result in bradycardia, hypotension, and even cardiac arrest. A detailed discussion on the problems which may arise in laparoscopic procedures resulting from insufflating of the cavity, in which the procedure is being carried out, is provided in a paper entitled “Cardiovascular and Ventilatory Consequences of Laparoscopic Surgery” by Atkinson, Giraud, Togioka, Jones and Cigarroa, February 14, 2017 [Circulation. 2017; 135:700-710. DOI: 10.1161/CIRCULATIONAHA.116.023262].

Once the peritoneal cavity has been insufflated to the target cavity pressure, it is important that the cavity pressure be controlled in order to avoid the peak airway pressure of the subject exceeding a maximum safe peak airway pressure value. It has been found that insufflating the peritoneal cavity of a subject results in the diaphragm that separates the peritoneal cavity from the thoracic cavity of a subject moving upwardly into the thoracic cavity. This upward movement of the diaphragm results in the pressure being applied to the lungs increasing. This increase in the pressure applied to the lungs results in an increase in the airway pressure in the airway of a subject, which may result in damage to the lungs of the subject, and may also compromise the blood circulatory system. The insufflating of a vessel or an organ in the peritoneal cavity, may also result in upward movement of the diaphragm separating the peritoneal cavity from the thoracic cavity being urged into the thoracic cavity which may also result in an increase in the airway pressure of a subject and in turn the peak airway pressure of the subject. For example, insufflating the stomach of a subject may similarly result in upward movement of the diaphragm into the thoracic cavity, which would in turn result in an increase in the airway pressure of the subject.

Additionally, during insufflating of the peritoneal cavity, if is also important to control the cavity pressure so that the heart rate of a subject or other characteristic of the performance of the heart of a subject, for example, the blood pressure of the subject, does not fall below certain predefined minimum values, otherwise, the heart of the subject may be compromised, and if the relevant characteristic of the performance of the heart dropped to a particularly low level, cardiac arrest may follow, and the life of (he subject may be at risk.

Additionally, both during a minimally invasive procedure, and indeed towards the end of a minimally invasive procedure, it is important at all stages to monitor the depth of anaesthesia of the subject. This is particularly important towards the end of the procedure, to ensure that the depth of anaesthesia of the subject is maintained at an appropriate level.

Accordingly, it is important during insufflating of the peritoneal cavity of a subject and in some cases during insufflating of a cavity, vessel or organ within the peritoneal cavity, that the insufflating of the cavity be controlled such that the rate of insufflating of the cavity does not exceed a safe insufflating rate, that the cavity pressure should be controlled in order to avoid the peak airway pressure of the subject exceeding a maximum safe peak airway pressure value, and also that the heart rate or other characteristic of the performance of the heart of a subject should not fall below a predefined minimum characteristic value, and in some cases, should not exceed a predefined maximum characteristic value, and it is also important that the depth of anaesthesia of the subject be monitored.

There is therefore a need for an insufflator for insufflating a cavity in the body of a human or animal subject which addresses at least one, and preferably, some if not all of the above issues, and there is also a need for a method for insufflating a cavity in the body of a human or animal subject which also addresses at least one or some, and preferably, all of the above issues.

The present invention is directed towards providing an insufflator for insufflating a cavity in the body of a human or animal subject, and a method for insufflating a cavity in the body of a human or animal subject which addresses at least one of the above issues. According to the invention there is provided an insufflator for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the insufflator comprising: a flow controller adapted for controlling the delivery of insufflating gas to the cavity, a first receiving means adapted for receiving a signal indicative of airway pressure in the airway of the subject, an electronic memory adapted to store a maximum safe airway pressure value, and a signal processor programmed to read the value of the signal indicative of the airway pressure of (he subject from the first receiving means, to compare the read value of the signal indicative of the airway pressure of the subject with the stored maximum safe airway pressure value, and to operate the flow controller to reduce the pressure in the cavity (cavity pressure) in response to the read value of the signal indicative of the airway pressure of the subject exceeding the maximum safe airway pressure value.

Preferably, the maximum safe airway pressure value is stored as a maximum safe peak airway pressure value.

Advantageously, the airway pressure of the subject which is compared with the maximum safe peak airway pressure value is the peak airway pressure value of the subject, and the signal processor is programmed to operate the flow controller to reduce the cavity pressure in response to the peak airway pressure value of the subject exceeding the stored maximum safe peak airway pressure value.

In one embodiment of the invention the signal processor is programmed to operate the flow controller to reduce the cavity pressure by reducing the rate of delivery of insufflating gas to the cavity.

In another embodiment of the invention the signal processor is programmed to operate the flow controller to reduce the cavity pressure by temporarily terminating delivery of insufflating gas to the cavity.

Preferably, the insufflator comprises a pressure reducing means configured to reduce the cavity pressure, the signal processor being programmed to operate the pressure reducing means for reducing the cavity pressure in response to the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

In one embodiment of the invention the pressure reducing means comprises a venting means for venting the cavity. Preferably, the venting means comprises a venting valve.

In another embodiment of the invention the pressure reducing means comprises a vacuum applying means for applying a vacuum to the cavity. Preferably, the vacuum applying means comprises a vacuum pump. Alternatively, the vacuum applying means comprises a communicating means for selectively communicating the cavity with a vacuum source. Preferably, the communicating means comprises an isolating valve alternately operable in a communicating state communicating the cavity with the vacuum source, and in an isolating state isolating the cavity from the vacuum source.

In one embodiment of the invention the signal processor is programmed to operate the flow controller and/or the pressure reducing means to reduce the cavity pressure in incremental pressure reducing steps in response to the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

Preferably, the signal processor is programmed to operate the flow controller and/or the pressure reducing means for maintaining the cavity pressure substantially constant at the current reduced cavity pressure value for a predefined dwell time interval each time the cavity pressure is reduced by one of the incremental pressure reducing steps.

In one embodiment of the invention the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is the same as the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

In an alternative embodiment of the invention the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is greater than or less than the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

In one embodiment of the invention the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step plus the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps.

In another embodiment of the invention the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value in the range of 1.5 times to 3 times the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step. Preferably, the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value of approximately twice the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

In one embodiment of the invention each predefined dwell time interval lies in the range of 0.5 minutes to 2 minutes. Preferably, each predefined dwell time interval lies in the range of 0.75 minutes to 1.5 minutes. Advantageously, each predefined dwell time interval is approximately 1 minute.

In one embodiment of the invention the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps lies in the range of 0.5mmHg to 2mmHg. Preferably, the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps is approximately 1 mmHg.

In one embodiment of the invention the signal processor is programmed to operate the flow controller and/or the pressure reducing means to reduce the cavity pressure until the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

In another embodiment of the invention the signal processor is programmed to operate the flow controller and/or the pressure reducing means to cease reducing the cavity pressure in response to the cavity pressure being reduced to a predefined minimum cavity pressure value before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

In another embodiment of the invention the signal processor is programmed to operate the flow controller and/or the pressure reducing means to maintain the cavity pressure at a reduced cavity pressure value corresponding to the cavity pressure value at which the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or at the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to (he maximum safe peak airway pressure value.

Preferably, the signal processor is programmed to produce a warning signal convertible to a human sensory perceptible signal in response to the cavity pressure being reduced to the predefined minimum cavity pressure value.

Preferably, the predefined minimum cavity pressure value comprises a cavity pressure value consistent with producing a minimum working volume in the cavity. Advantageously, the predefined minimum cavity pressure value lies in the range of 3mmHg to 8mmHg. Ideally, the predefined minimum cavity pressure value is approximately 5mmHg.

In one embodiment of the invention the first receiving means is adapted for receiving the signal indicative of the airway pressure or the peak airway pressure of the subject electronically. Preferably, the first receiving means comprises a receiving port configured for coupling to a wire electronically carrying the signal indicative of the airway pressure or the peak airway pressure of the subject. Alternatively, the first receiving means comprises a first wireless receiver for receiving the signal indicative of the airway pressure or the peak airway pressure of the subject.

In one embodiment of the invention the signal indicative of the airway pressure or the peak airway pressure of the subject is derived from an airway pressure monitoring means adapted to monitor the airway pressure of the subject.

In another embodiment of the invention the airway pressure monitoring means comprises an airway pressure monitoring sensor of an anaesthesia control and monitoring machine controlling and monitoring the depth of anaesthesia of the subject. Alternatively, the airway pressure monitoring means comprises an airway pressure monitoring sensor located in a ventilator ventilating the subject.

In a further alternative embodiment of the invention the insufflator comprises the airway pressure monitoring means, and the airway pressure monitoring means is adapted for coupling to an endotracheal tube through which the subject is being ventilated.

In one embodiment of the invention the airway pressure monitoring means is adapted to produce a signal indicative of the peak airway pressure value of the subject.

In an alternative embodiment of the invention the airway pressure monitoring means is adapted to produce a signal indicative of the airway pressure of the subject, and preferably, the signal processor is programmed to determine the peak airway pressure of the subject from the signal produced by the airway pressure monitoring means indicative of the airway pressure of the subject.

In another embodiment of the invention a cavity pressure monitoring means is provided, the cavity pressure monitoring means being adapted to monitor the cavity pressure and to produce a signal indicative of the cavity pressure, and the signal processor is programmed to read the signal indicative of the cavity pressure produced by the cavity pressure monitoring means. Preferably, the signal processor is programmed to operate the flow controller and/or the pressure reducing means in response to the signal indicative of the cavity pressure read from the cavity pressure monitoring means for maintaining the cavity pressure at a target pressure value until the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value.

In one embodiment of the invention the signal processor is programmed to operate the flow controller and/or the pressure reducing means in response to the signal indicative of the cavity pressure read from the cavity pressure monitoring means for maintaining the cavity pressure at a pressure not exceeding a value equal to the maximum safe peak airway pressure value, or at a pressure below or just below the value of the maximum safe peak airway pressure value.

In another embodiment of the invention the insufflator comprises an insufflating monitoring means for monitoring insufflating of the cavity and for producing a signal indicative of the insufflating of the cavity, and the signal processor is programmed to read the signal produced by the insufflating monitoring means indicative of the insufflating of the cavity, to determine the rate at which the cavity is being insufflated from the signal read from the insufflating monitoring means, to compare the determined rate at which the cavity is being insufflated with a stored maximum insufflating rate value stored in the electronic memory, and to operate the flow controller to prevent the rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

Preferably, the signal processor is programmed to operate the flow controller to reduce the flow rate at which insufflating gas is being delivered to the cavity or to temporarily pause delivery of insufflating gas to the cavity in response to the determined rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

In one embodiment of the invention the stored maximum insufflating rate value is stored as a function of cavity pressure. Preferably, the signal processor is programmed to determine the rate at which the cavity is being insufflated as a function of the cavity pressure.

In another embodiment of the invention the stored maximum insufflating rate value is stored as a value of a maximum increase in cavity pressure per unit time. Preferably, the signal processor is programmed to determine the rate at which the cavity is being insufflated as the increase in the cavity pressure per unit time. In one embodiment of the invention the insufflating monitoring means for monitoring insufflating of the cavity comprises the cavity pressure monitoring means configured to monitor the cavity pressure.

In an alternative embodiment of the invention the stored maximum insufflating rate value is stored as a function of the flow of the insufflating gas delivered to the cavity. Preferably, the signal processor is programmed to determine the rate at which the cavity is being insufflated as a function of the flow of the insufflating gas being delivered to the cavity.

In another embodiment of the invention the stored maximum insufflating rate value is stored as a value of a maximum rate of delivery of insufflating gas to the cavity. Preferably, the signal processor is programmed to determine the rate at which the cavity is being insufflated as the flow rate at which the insufflating gas is being delivered to the cavity.

In one embodiment of the invention the insufflating monitoring means comprises a flow sensor for monitoring the flow of insufflating gas to the cavity and for producing a signal indicative of the flow of insufflating gas to the cavity.

Preferably, a plurality of maximum insufflating rate values are stored in the electronic memory for respective subjects of different types. Advantageously, a plurality of maximum insufflating rate values are stored for subjects of respective different ages or different age ranges. Preferably, a plurality of maximum insufflating rate values are stored for subjects of respective different weights or different weight ranges. Preferably, a plurality of maximum insufflating rate values are stored for subjects of respective different body mass indices or different body mass index ranges. Advantageously, a plurality of maximum insufflating rate values are stored for subjects of different sexes.

In one embodiment of the invention a plurality of maximum insufflating rate values are stored for different cavities of the respective different subjects.

In one embodiment of the invention a plurality of maximum insufflating rate values are stored for the peritoneal cavity of the respective different types of subjects.

In another embodiment of the invention a predefined minimum value of a characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall is stored in the electronic memory, and the signal processor is programmed to read a value of a signal indicative of a characteristic of the performance of the heart of the subject, to compare the read value of the signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined minimum value of the characteristic, and to operate the flow controller to reduce the rate of delivery of insufflating gas to the cavity or to cease delivery of insufflating gas to the cavity, or to operate the pressure reducing means to reduce the cavity pressure in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the stored predefined minimum value of the characteristic.

Preferably, the signal processor is programmed to operate the pressure reducing means to vent or withdraw insufflating gas from the cavity in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the stored predefined minimum value of the characteristic.

Advantageously, the predefined minimum value of the characteristic indicative of the performance of the heart of the subject stored in the electronic memory comprises a predefined minimum value of the heart rate of a subject, below which the heart rate of a subject should not fall, and the signal processor is programmed to read a signal indicative of the characteristic of the performance of the heart of the subject as the heart rate of the subject.

In another embodiment of the invention a predefined maximum value of a characteristic indicative of a maximum performance value, above which the performance of a heart of a subject should not exceed is stored in the electronic memory, and the signal processor is programmed to read a value of a signal indicative of a characteristic of the performance of the heart of the subject, to compare the read value of the signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined maximum value of the characteristic, and to operate the flow controller to reduce the rate of delivery of insufflating gas to the cavity or to cease delivery of insufflating gas to the cavity, or to operate the pressure reducing means to reduce the cavity pressure in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject exceeding the stored predefined maximum value of the characteristic.

Preferably, the signal processor is programmed to operate the pressure reducing means to vent or withdraw insufflating gas from the cavity in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject exceeding the stored predefined maximum value of the characteristic.

Advantageously, the predefined maximum value of the characteristic indicative of the performance of the heart of the subject stored in the electronic memory comprises a predefined maximum value of the heart rate of a subject, above which the heart rate of a subject should not exceed, and the signal processor is programmed to read a signal indicative of the characteristic of the performance of the heart of the subject as the heart rate of the subject.

In one embodiment of the invention the insufflator comprises a second receiving means adapted for receiving the signal indicative of the characteristic of the performance of the heart of the subject, and the signal processor is programmed to read the signal indicative of the characteristic of the performance of the heart of the subject from the second receiving means.

Preferably, the second receiving means comprises a second receiving port configured for coupling to a wire electronically carrying the signal indicative of the characteristic of the performance of the heart of the subject, or a second wireless receiver for wirelessly receiving the signal indicative of the characteristic of the performance of the heart of the subject.

Preferably, a heart performance monitoring means is provided for monitoring the characteristic indictive of the performance of the heart of a subject and to produce a signal indicative of the characteristic of the performance of the heart of the subject from the heart performance monitoring means.

Advantageously, the heart performance monitoring means for monitoring the characteristic indicative of the performance of the heart of a subject is adapted for monitoring the heart rate of the subject.

In one embodiment of the invention the signal processor is programmed to operate the flow controller to cease delivery of insufflating gas to the cavity in response to the monitored characteristic of the performance of the heart of the subject falling below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject, or exceeding the predefined maximum value of the characteristic indicative of the performance of the heart of a subject, and preferably, simultaneously with operating the flow controller to cease delivery of insufflating gas to the cavity of the subject, the signal processor is programmed to commence timing a predefined first delay time period. Advantageously, the signal processor is programmed to operate the pressure reducing means to reduce the cavity pressure to the predefined minimum cavity pressure value at the end of the predefined first delay time period in response to the monitored characteristic being below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject or exceeding the predefined maximum value of the characteristic indicative of the performance of the heart of a subject.

In one embodiment of the invention the signal processor is programmed in response to the cavity pressure being reduced to the predefined minimum cavity pressure value to commence timing a predefined second delay time period, and preferably, the signal processor is programmed to output a warning signal at the end of the predefined second delay time period in response to the monitored characteristic being below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject or exceeding the predefined maximum value of the characteristic indicative of the performance of the heart of a subject, indicating that the monitored characteristic is below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject, or exceeds the predefined maximum value of the characteristic indicative of the performance of the heart of a subject, and the cavity pressure has been reduced to the predefined minimum cavity pressure value.

In one embodiment of the invention the predefined first delay time period lies in the range of 10 seconds to 2 minutes, and preferably, lies in the range of 20 seconds to 1 minute, and advantageously', is approximately 30 seconds.

In another embodiment of the invention the predefined second delay time period lies in the range of 10 seconds to 2 minutes, and preferably, lies in the range of 20 seconds to 1 minute, and advantageously, is approximately 30 seconds.

In another embodiment of the invention the predefined minimum value of the characteristic indicative of the performance of the heart of a subject is stored as a predefined minimum value of the blood pressure of a subject.

In another embodiment of the invention the predefined maximum value of the characteristic indicative of the performance of the heart of a subject is stored as a predefined maximum value of the blood pressure of a subject.

Preferably, the signal processor is programmed to read a signal indicative of the blood pressure of the subject and to compare the read value of the blood pressure of the subject with the predefined minimum value of the blood pressure of a subject and/or the predefined maximum value of the blood pressure of a subject.

In one embodiment of the invention the predefined minimum value of the blood pressure of a subject is stored as either or both of a predefined minimum value of the systolic pressure or a predefined minimum value of the diastolic pressure of the blood pressure of a subject, and in another embodiment of the invention the predefined maximum value of the blood pressure of a subject is stored as either or both of a predefined maximum value of the systolic pressure or a predefined maximum value of the diastolic pressure of the blood pressure of a subject.

In one embodiment of the invention the means for monitoring the characteristic indicative of the performance of the heart of a subject comprises a means for monitoring the blood pressure of a subject.

In one embodiment of the invention an interface is provided, and the signal processor is programmed to read signals and data inputted through the interface and to store the inputted data in the electronic memory. Preferably, the interface is adapted for inputting of the target pressure value at which the cavity is to be insufflated. Advantageously, the interface is adapted for inputting the maximum safe peak airway pressure value.

In one embodiment of the invention the interface is adapted for inputting the predefined minimum value of the characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall, and/or the predefined maximum value of a characteristic indicative of the maximum performance value above which the performance of a heart of a subject should not exceed.

In another embodiment of the invention the interface is adapted for inputting at least one or more of the sex, the age or the age range, weight or weight range, or the body mass index or the body mass index range of the subject, and preferably, the signal processor is programmed to select the appropriate maximum insufflating rate value from the stored values thereof in response to data indicative of at least one of the sex, the age or the age range, the weight or the weight range, or the body mass index or the body mass index range of the subject entered through the interface.

In another embodiment of the invention the signal processor is programmed to store a default value of the maximum insufflating rate of a subject, and preferably, the default value of the maximum insufflating rate of a subject comprises the maximum insufflating rate stored for a subject of at least one of a subject of female sex, of the youngest age or age range, the lowest weight or weight range and/or the lowest body mass index or body mass index range.

In one embodiment of the invention the signal processor is programmed to monitor a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure read from the cavity pressure monitoring means, to determine the depth of anaesthesia or change in the depth of anaesthesia of the subject from the monitored characteristic indicative of the depth of anaesthesia, and to produce a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject.

In another embodiment of the invention the characteristic indicative of the depth of anaesthesia of the subject monitored by the signal processor from the signal indicative of the cavity pressure read from the cavity pressure monitoring means comprises an alternating component of the signal indicative of the cavity pressure.

Preferably, the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

Advantageously, the signal processor is programmed to determine the depth of anaesthesia or the change in the depth of anaesthesia of the subject as a function of the pressure differential between consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure.

Additionally, the invention provides an insufflator for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the insufflator comprising: a flow controller adapted for controlling the delivery of insufflating gas to the cavity, one or both of a first receiving means adapted for receiving a signal indicative of airway pressure in the airway of the subject, and/or a second receiving means adapted for receiving a signal indicative of a characteristic of the performance of the heart of the subject, an electronic memory adapted to store one or both of a maximum safe airway pressure value, and/or a predefined minimum value of a characteristic indicative of the performance of the heart of a subject, and a signal processor programmed to read the signal indicative of the airway pressure of the subject from the first receiving means, and/or to read the signal indicative of the characteristic of the performance of the heart of the subject, to compare the read signal indicative of the airway pressure of the subject with the stored maximum safe airway pressure value, and/or to compare the read signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined minimum value of the characteristic indicative of the performance of the heart of a subject, and to operate the flow controller to one of reduce the rate of delivery of insufflating gas to the cavity of the subject, or to cease delivery of insufflating gas to the cavity of the subject for reducing the cavity pressure, in response to the read value indicative of the airway pressure of the subject exceeds the maximum safe airway pressure value, or in response to the read value indicative of the characteristic of the performance of the heart of the subject falling below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject.

Preferably, a predefined maximum value of a characteristic indicative of the performance of the heart of a subject is stored in the electronic memory, and the signal processor is programmed to compare the read signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined maximum value of the characteristic indicative of the performance of the heart of a subject.

In one embodiment of the invention the signal processor is programmed to operate the flow controller to one of reduce the rate of delivery of insufflating gas to the cavity of the subject or to cease delivery of insufflating gas to the cavity of the subject for reducing the cavity pressure, in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject exceeding the predefined maximum value of the characteristic stored in memory.

Preferably, a pressure reducing means is provided for reducing the cavity pressure, and the signal processor is programmed to operate the pressure reducing means to reduce the cavity pressure in response to the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value, or the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject, or exceeding the predefined maximum value of the characteristic indicative of the performance of the heart of a subject.

Preferably, the signal processor is programmed to operate the flow controller and/or the pressure reducing means to reduce the cavity pressure in incremental pressure reducing steps.

Preferably, the signal processor is programmed to operate the flow controller and/or the pressure reducing means for maintaining the cavity pressure substantially constant at the current cavity pressure for a predefined dwell time interval at the end of each incremental pressure reducing step.

Advantageously, the signal processor is programmed to reduce the cavity pressure by an incremental pressure value in each incremental pressure reducing step.

In another embodiment of the invention the signal processor is programmed to operate the flow controller and/or the pressure reducing means to maintain the cavity pressure at a reduced cavity pressure corresponding to the cavity pressure value at which the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or the read value of the signal indicative of the characteristic of the performance of the heart of the subject being within the predefined minimum value of the characteristic indicative of the performance of the heart of the subject, and the predefined maximum value of the characteristic indicative of the performance of the heart of the subject, whichever is the lowest cavity pressure, or at the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or the characteristic indicative of the performance of the heart of the subject is within the predefined minimum and maximum values of the characteristic thereof.

Preferably, the signal processor is programmed to produce a warning signal convertible to a human sensory perceptible signal warning that the cavity pressure has been reduced to the predefined minimum cavity pressure value.

In one embodiment of the invention the signal processor is programmed to operate the flow controller and/or the pressure reducing means in response to the signal read from the cavity pressure monitoring means for maintaining the cavity pressure at a target pressure value, until the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value, the signal indicative of the characteristic of the performance of the heart of the subject is below the predefined minimum value of the characteristic indicative of the performance of the heart of the subject or is above the predefined maximum value of the characteristic indicative of the performance of the heart of the subject.

In another embodiment of the invention the insufflator comprises an insufflating monitoring means for monitoring insufflating of the cavity and for producing a signal indicative of the insufflating of the cavity, the signal processor being programmed to read the signal produced by the insufflating monitoring means indicative of the insufflating of the cavity, to determine the rate at which the cavity is being insufflated from the signal read from the insufflating monitoring means, to compare the determined rate at which the cavity is being insufflated with a stored maximum insufflating rate value stored in the electronic memory, and to operate the flow controller to prevent the rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

The invention also provides an insufflator for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the insufflator comprising a flow controller for controlling delivery of insufflating gas to the cavity, a cavity pressure monitoring means for monitoring pressure in the cavity and producing a signal indicative of the cavity pressure, and a signal processor programmed to read the signal indicative of the cavity pressure produced by the cavity pressure monitoring means, and to operate the flow controller to deliver insufflating gas to the cavity and to maintain the cavity pressure at a target pressure value or a pressure value below the target pressure value in response to the signal indictive of the cavity pressure read from the cavity pressure monitoring means, the signal processor being further programmed to monitor a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure read from the cavity pressure monitoring means, to determine the depth of anaesthesia or change in the depth of anaesthesia of the subject from the monitored characteristic indicative of the depth of anaesthesia, and to produce a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject.

In one embodiment of the invention the characteristic indicative of the depth of anaesthesia of the subject monitored by the signal processor from the signal indicative of the cavity pressure read from the cavity pressure monitoring means comprises an alternating component of the signal indicative of the cavity pressure.

Preferably, the signal processor is programmed to determine the depth of anaesthesia or the change in the depth of anaesthesia of the subject as a function of the pressure differential between consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure.

Advantageously, the signal processor is programmed to monitor the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure.

Preferably, the signal processor is programmed to determine an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure as being indicative of a decrease in the depth of anaesthesia of the subject.

In one embodiment of the invention the signal processor is programmed to determine a baseline value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or a baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure, and to store the determined baseline value of the pressure differential or the determined baseline value of the frequency in an electronic memory of the signal processor or accessible thereto.

Preferably, the baseline value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure is determined by the signal processor as the value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure that corresponds with the optimum depth of anaesthesia of the subject.

In one embodiment of the invention an upper pressure differential increase value is stored in the electronic memory or an upper frequency increase value is stored in the electronic memory, the upper pressure differential increase value and the upper frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of a pair thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention in the anaesthesia of the subject is required, and the signal processor is programmed to compare an increase in the current value of the pressure differential between the current pair of the consecutive upper and lower peak values above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure with the corresponding one of the upper pressure differential increase value or the upper frequency increase value, and to output a warning signal in response to the increase in the current value of the pressure differential between the current pair of the consecutive upper and lower peak values above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure exceeding the corresponding one of the upper pressure differential increase value or the upper frequency increase value.

In another embodiment of the invention a lower pressure differential increase value is stored in the electronic memory or a lower frequency increase value is stored in the electronic memory, the lower pressure differential increase value and the lower frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of a pair thereof or an increase in the frequency of (he alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention of an anaesthetist should be considered, and the signal processor is programmed to compare an increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure with the corresponding one of the lower pressure differential increase value or the lower frequency increase value, and to output an alert signal in response to the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure exceeding the corresponding one of the lower pressure differential increase value or the lower frequency increase value.

Preferably, the warning signal and the alert signal are convertible to a human sensory perceptible signal.

In another embodiment of the invention the signal processor is programmed to monitor both the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure.

In another embodiment of the invention the signal processor is programmed to determine the depth or the change in the depth of anaesthesia of the subject as a function of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure.

Preferably, the signal processor is programmed to produce the signal indicative of the depth of anaesthesia of the subject for conversion to a visually perceptible form.

Advantageously, the signal processor is programmed to produce the signal indictive of the depth of anaesthesia of the subject as a waveform.

In one embodiment of the invention the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of the change in the differential pressure between the consecutive upper and lower peak values of consecutive pairs thereof with respect to time or the change in the frequency value with respect to time of the alternating component of the signal indicative of cavity pressure plotted against time.

In another embodiment of the invention the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of a combination of the change in the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof with respect to time and the change in the frequency value with respect to time of the alternating component of the signal indicative of the cavity pressure plotted against time.

In one embodiment of the invention a first receiving means is provided for receiving a signal indicative of the airway pressure or the peak airway pressure of the subject, and the signal processor is programmed to read the signal indicative of the airway pressure or the peak airway pressure from the first receiving means and to compare the read value of the signal indicative of the airway pressure or the peak airway pressure of the subject with a maximum safe peak airway pressure value, and the signal processor is programmed to operate the flow controller to reduce the cavity pressure in response to the airway pressure or the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

Further the invention provides apparatus for monitoring the depth of anaesthesia or change in the depth of anaesthesia of a subject during a minimally invasive procedure in the peritoneal cavity of a subject or in a cavity, in a vessel or an organ within the peritoneal cavity of the subject during insufflating of the cavity to a target pressure value or a pressure value below the target pressure value, the apparatus comprising a signal processor programmed to read a signal produced by a cavity pressure monitoring means indicative of the pressure in the cavity (cavity pressure), the signal processor being programmed to monitor a characteristic indicative of the depth of anaesthesia of the subject from the signal read from the pressure sensor indicative of the cavity pressure, to determine the depth of anaesthesia or the change in the depth of anaesthesia of the subject from the monitored characteristic indicative of the depth of anaesthesia, and to produce a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject.

The invention also provides a method for insufflating the peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the method comprising delivering insufflating gas to the cavity, monitoring the pressure in the cavity (cavity pressure), monitoring the airway pressure of the subject during insufflating of the cavity, comparing the airway pressure of the subject with a maximum safe peak airway pressure value, and reducing the cavity pressure by reducing or temporarily terminating the supply of insufflating gas to the cavity in response to the airway pressure of the subject exceeding the maximum safe peak airway pressure value.

In one embodiment of the invention the cavity pressure is reduced by venting or withdrawing insufflating gas from the cavity.

In another embodiment of the invention the insufflating gas is withdrawn from the cavity by applying a vacuum to the cavity.

Preferably, the cavity pressure is reduced in incremental pressure reducing steps in response to the airway pressure of the subject exceeding the maximum safe peak airway pressure value.

Preferably, the cavity pressure is maintained substantially constant at the current reduced cavity pressure value for a predefined dwell time interval each time the cavity pressure is reduced by one of the incremental pressure reducing steps.

Preferably, the cavity pressure is reduced until the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

In one embodiment of the invention if the cavity pressure is reduced to a predefined minimum cavity pressure before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, delivery of insufflating gas to the cavity is terminated.

In another embodiment of the invention the cavity pressure is maintained at a reduced cavity pressure corresponding to the cavity pressure at which the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value or at the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

Preferably, a warning signal convertible to a human sensory perceptible signal is produced in response to the cavity pressure being reduced to the predefined minimum cavity pressure value.

In one embodiment of the invention the predefined minimum cavity pressure value is a cavity pressure value consistent with producing a minimum working volume in the cavity.

Preferably, the cavity pressure is maintained at a target pressure value until the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value.

In one embodiment of the invention the rate at which the cavity is being insufflated is determined and is compared with a maximum insufflating rate value, and the rate at which the cavity is being insufflated is reduced in response to the rate at which the cavity is being insufflated exceeding the maximum insufflating rate value.

In one embodiment of the invention the maximum insufflating rate value is defined as a function of cavity pressure. Preferably, the rate at which the cavity is being insufflated is determined as a function of the cavity pressure.

In another embodiment of the invention the maximum insufflating rate value is defined as a value of a maximum increase in cavity pressure per unit time.

Preferably, the rate at which the cavity is being insufflated is determined as the increase in the cavity pressure per unit time.

In another embodiment of the invention the maximum insufflating rate value is defined as a function of the flow of the insufflating gas delivered to the cavity. Preferably, the rate at which the cavity is being insufflated is determined as a function of the flow at which the insufflating gas is being delivered to the cavity.

In another embodiment of the invention the maximum insufflating rate value is defined as a value of a maximum rate of delivery of insufflating gas to the cavity. Preferably, the rate at which the cavity is being insufflated is determined as the flow rate at which the insufflating gas is being delivered to the cavity.

Preferably, a plurality of maximum insufflating rate values are defined for respective subjects of different types.

Advantageously, a plurality of maximum insufflating rate values are defined for subjects of one or more of different ages or different age ranges, of different weights or different weight ranges, of different body mass indices or different body mass index ranges, or of different sexes.

In another embodiment of the invention a plurality of maximum insufflating rate values are defined for different cavities of the respective different subjects.

Preferably, a plurality of maximum insufflating rate values are defined for the peritoneal cavity of the respective different types of subjects.

In one embodiment of the invention a characteristic indicative of the performance of the heart of the subject is determined and compared with a predefined minimum value of a characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall and/or a predefined maximum value of a characteristic indicative of maximum performance value above which the performance of a heart of a subject should not exceed, and delivery of insufflating gas to the cavity is paused or terminated or insufflating gas is withdrawn or vented from the cavity in response to the value of the characteristic indicative of the performance of the heart of the subject falling below the predefined minimum value of the characteristic, or rising above the predefined maximum value of the characteristic.

In one embodiment of the invention delivery of insufflating gas to the cavity is terminated in response to the monitored characteristic indicative of the performance of the heart of the subject falling below the predefined minimum valve of the characteristic indicative of the performance of the heart of a subject or exceeding the predefined maximum value of the characteristic indicative of the performance of the heart of a subject, and preferably, simultaneously with terminating delivery of insufflating gas to the cavity of the subject, timing of a predefined first delay time period is commenced. Advantageously, insufflating gas is withdrawn from the cavity of the subject to reduce the cavity pressure to the predefined minimum cavity pressure value at the end of the predefined first delay time period in response to the monitored characteristic being below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject or exceeding the predefined maximum value of the characteristic indicative of the performance of the heart of a subject.

In another embodiment of the invention timing of a predefined second delay time period is commenced on the cavity pressure being reduced to the predefined minimum cavity pressure value, and preferably, a warning signal is outputted at the end of the predefined second delay time period in response to the monitored characteristic being below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject or exceeding the predefined maximum value of the characteristic indicative of the heart of a subject, indicating that the monitored characteristic is below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject or exceeds the predefined maximum value of the characteristic indicative of the performance of the heart of a subject, and the cavity pressure has been reduced to the predefined minimum cavity pressure value.

Preferably, the predefined minimum value of the characteristic indicative of the performance of the heart of the subject comprises a minimum value of the heart rate of a subject below which the heart rate of a subject should not fall, the characteristic indicative of the performance of the heart of the subject is determined as the heart rate of the subject.

Advantageously, the predefined maximum value of the characteristic indicative of the performance of the heart of the subject comprises a maximum value of the heart rate of a subject above which the heart rate of a subject should not exceed, and the characteristic indicative of the performance of the heart of the subject is determined as the heart rate of the subject.

Preferably, the characteristic indictive of the performance of the heart of a subject is determined from a signal from a heart performance monitoring means.

Advantageously, the characteristic indicative of the performance of the heart of a subject is determined from a heart rate monitoring means.

Preferably, a signal indicative of the blood pressure of the subject is compared with the predefined minimum value of the blood pressure of a subject and/or the predefined maximum value of the blood pressure of a subject.

In one embodiment of the invention the predefined minimum value of the blood pressure of a subject is stored as either or both of a predefined minimum value of the systolic pressure or a predefined minimum value of the diastolic pressure of the blood pressure of a subject, and in another embodiment of the invention the predefined maximum value of the blood pressure of a subject is stored as either or both of a predefined maximum value of the systolic pressure or a predefined maximum value of the diastolic pressure of the blood pressure of a subject. Additionally, the invention provides a method for insufflating the peritoneal cavity, or a cavity in a vessel or organ in the peritoneal cavity, the method comprising delivering insufflating gas to the cavity, monitoring the pressure in the cavity (cavity pressure) by a pressure sensor adapted to produce a signal indicative of the cavity pressure, controlling delivery of insufflating gas to the cavity in response to the signal indicative of the cavity pressure to maintain the cavity pressure at a target pressure value or a pressure value below the target pressure value, monitoring a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure, and producing a human sensory perceptible signal indicative of the depth of anaesthesia or change in the depth of anaesthesia of the subject.

In one embodiment of the invention the characteristic indicative of the depth of anaesthesia of the subject monitored from the signal indicative of the cavity pressure produced by the pressure sensor comprises an alternating component of the signal indicative of the cavity pressure.

Preferably, the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm of the subject separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

In one embodiment of the invention the depth of anaesthesia or the change in the depth of anaesthesia of the subject is determined as a function of the pressure differential between the consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure.

Preferably, the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure is monitored.

Preferably, an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure is determined as being indicative of a decrease in the depth of anaesthesia of the subject.

In one embodiment of the invention a baseline value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or a baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure is determined.

Preferably, the baseline value of the pressure differential or the baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure is determined as the value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure that corresponds with the optimum depth of anaesthesia of the subject.

In one embodiment of the invention the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure is compared with an upper pressure differential increase value or an upper frequency increase value, the upper pressure differential increase value and the upper frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of a pair thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention by an anaesthetist in the anaesthesia of the subject is required, and a warning signal is produced in response to either the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof exceeding the corresponding one of the upper pressure differential increase value or the upper frequency increase value.

In another embodiment of the invention the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure is compared with a lower pressure differential increase value or a lower frequency increase value, the lower pressure differential increase value and the lower frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of the current pair thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention by an anaesthetist in the anaesthesia of the subject should be considered, and an alert signal is produced in response to either the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof exceeding the corresponding one of the lower pressure differential increase value or the lower frequency increase value.

Preferably, the warning signal and the alert signal are convertible to a human sensory perceptible signal. In one embodiment of the invention both the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure are monitored.

In another embodiment of the invention the depth of anaesthesia or the change in the depth of anaesthesia of the subject is determined as a function of the pressure differential between the consecutive upper and lower peak values and the frequency of the alternating component of the signal indicative of the cavity pressure.

Preferably, the signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject is adapted for conversion to a visually perceptible signal.

Preferably, the signal indictive of the depth of anaesthesia of the subject is produced as a waveform.

Advantageously, the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of the change in the values of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time or the change in the frequency values with respect to time of the alternating component of the signal indicative of cavity pressure plotted against time.

Preferably, the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of a combination of the change in the values of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time and the change in the frequency values with respect to time of the alternating component of the signal indicative of the cavity pressure plotted against time.

In one embodiment of the invention the airway pressure of the subject is monitored during insufflating of the cavity of the subject and compared with a maximum safe airway pressure value and preferably, a maximum safe peak airway pressure value, and preferably, the cavity pressure is reduced by reducing or temporarily terminating the supply of insufflating gas to the cavity or by venting or withdrawing insufflating gas from the cavity in response to the airway pressure of the subject exceeding the maximum safe peak airway pressure value.

The invention also provides a method for monitoring the depth of anaesthesia or change in the depth of anaesthesia of a subject during a minimally invasive procedure in the peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity in which the cavity is being insufflated to a target pressure value or a pressure value below the target pressure value, the method comprising monitoring a signal indicative of the pressure in the cavity (cavity pressure), monitoring a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure, determining the depth of anaesthesia or the change in the depth of anaesthesia of the subject from the monitored characteristic, and producing a signal indicative of the depth of anaesthesia or change in the depth of anaesthesia of the subject.

Preferably, the characteristic indicative of the depth of anaesthesia of the subject monitored from the signal indicative of the cavity pressure comprises an alternating component of the signal indicative of the cavity pressure.

Advantageously, the alternating component of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm of the subject separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

Additionally, the invention provides a method for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject by an insufflator, the insufflator comprising: a flow controller for controlling the delivery of insufflating gas to the cavity, a first receiving means for receiving a signal indicative of airway pressure in the airway of the subject, and a stored maximum safe airway pressure value, the method comprising reading the value of the signal indicative of the airway pressure of the subject from the first receiving means, comparing the read value of the signal indicative of the airway pressure of the subject with the stored maximum safe airway pressure value, and operating the flow controller to reduce the pressure in the cavity (cavity pressure) in response to the read value of the signal indicative of the airway pressure of the subject exceeding the maximum safe airway pressure value. Preferably, the maximum safe airway pressure value is stored as a maximum safe peak airway pressure value.

In one embodiment of the invention the flow controller is operated to reduce the cavity pressure by reducing the rate of delivery of insufflating gas to the cavity.

In another embodiment of the invention the flow controller is operated to reduce the cavity pressure by temporarily terminating delivery of insufflating gas to the cavity.

In one embodiment of the invention the insufflator comprises a pressure reducing means configured to reduce the cavity pressure, and the pressure reducing means is operated for reducing the cavity pressure in response to the airway pressure of the subject exceeding the maximum safe peak airway pressure value.

In one embodiment of the invention the flow controller and/or the pressure reducing means are operated to reduce the cavity pressure in incremental pressure reducing steps in response to the read value of the signal indicative of the airway pressure in the subject exceeding the maximum safe peak airway pressure value.

Preferably, the flow controller and/or the pressure reducing means are operated for maintaining the cavity pressure substantially constant at the current reduced cavity pressure value for a predefined dwell time interval each time the cavity pressure is reduced by one of the incremental pressure reducing steps.

In another embodiment of the invention the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is the same as the incremental pressure value by which the cavity pressure was reduced during the immediately preceding incremental pressure reducing step.

In an alternative embodiment of the invention the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is greater than or less than the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step. In one embodiment of the invention the flow controller and/or the pressure reducing means is operated to reduce the cavity pressure until the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

In another embodiment of the invention the flow controller and/or the pressure reducing means are operated to cease reducing the cavity pressure below a predefined minimum cavity pressure if the cavity pressure is reduced to the predefined minimum cavity pressure before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

In another embodiment of the invention the flow controller and/or the pressure reducing means are operated to maintain the cavity pressure at a reduced current cavity pressure value corresponding to the cavity pressure value at which the read value of the signal indicative of the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to the maximum safe peak airway pressure value.

In one embodiment of the invention the insufflator comprises an insufflating monitoring means for monitoring insufflating of the cavity and for producing a signal indicative of the insufflating of the cavity, the method further comprises reading the signal produced by the insufflating monitoring means indicative of the insufflating of the cavity, determining the rate at which the cavity is being insufflated from the signal read from the insufflating monitoring means, comparing the determined rate at which the cavity is being insufflated with a stored maximum insufflating rate value, and operating the flow controller to prevent the rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

Preferably, the flow controller is operated to reduce the flow rate at which insufflating gas is being delivered to the cavity or to temporarily pause delivery of insufflating gas to the cavity in response to the determined rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

In one embodiment of the invention the stored maximum insufflating rate value is stored as a function of cavity pressure, and preferably, the rate at which the cavity is being insufflated is determined as a function of the cavity pressure.

In another embodiment of the invention the stored maximum insufflating rate value is stored as a value of a maximum increase in cavity pressure per unit time, and preferably, the rate at which the cavity is being insufflated is determined as the increase in the cavity pressure per unit time.

In one embodiment of the invention the stored maximum insufflating rate value is stored as a function of the flow of the insufflating gas delivered to the cavity, and preferably, the rate at which the cavity is being insufflated is determined as a function of the flow rate at which the insufflating gas is being delivered to the cavity.

In another embodiment of the invention the stored maximum insufflating rate value is stored as a value of a maximum rate of delivery of insufflating gas to the cavity, and preferably, the rate at which the cavity is being insufflated is determined as the flow rate at which the insufflating gas is being delivered to the cavity.

In one embodiment of the invention a predefined minimum value of a characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall or a predefined maximum value of a characteristic indicative of the maximum performance value above which the performance of a heart of a subject should not exceed are stored and the method further comprises reading a value of a signal indicative of a characteristic of the performance of the heart of the subject, comparing the read value of the characteristic of the performance of the heart of the subject with the stored predefined minimum value of the characteristic or the stored maximum value of the characteristic, and operating the insufflator to one of reduce the rate of delivery of insufflating gas to the cavity, or to cease delivery of insufflating gas to the cavity, or to operate the pressure reducing means to reduce the cavity pressure in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the stored predefined minimum value of the characteristic, or exceeding the stored predefined maximum value of the characteristic.

In another embodiment of the invention a characteristic indicative of the depth of anaesthesia or a change in the depth of anaesthesia of the subject is monitored from the signal indicative of the cavity pressure, and a signal indicative of the depth of anaesthesia or a change in the depth of anaesthesia of the subject is produced.

Preferably, the characteristic indicative of the depth of anaesthesia of the subject monitored from the signal indicative of the cavity pressure produced by the pressure sensor comprises an alternating component of the signal indicative of the cavity pressure.

Further the invention provides use of the insufflators according to the invention in insufflating a peritoneal cavity of a subject or insufflating a cavity in a vessel or an organ in the peritoneal cavity of the subject.

The advantages of the insufflators according to the invention are many. A particularly important advantage of the insufflators according to the invention is that there is no risk of the peak airway pressure of a subject rising to a level which would impair ventilating of the lungs of a subject or breathing by a subject as a result of insufflating of the peritoneal cavity, or other cavity within the peritoneal cavity, whereby the insufflating of the peritoneal cavity or such other cavity within the peritoneal cavity may result in the diaphragm separating the thoracic cavity from the peritoneal cavity being urged into the thoracic cavity by the pressure of the insufflating gas in the peritoneal cavity or in such other cavity being insufflated within the peritoneal cavity to the extent that the urging of the diaphragm into the thoracic cavity would raise the peak airway pressure in the airway of the subject to an extent that ventilating of or breathing by the subject would be impaired.

Another important advantage of the insufflators according to the invention is that the insufflators may be readily adapted to monitor the depth of anaesthesia of a subject during insufflating of the peritoneal cavity or during insufflating of a cavity within the peritoneal cavity. It has been found that by monitoring an alternating component of the cavity pressure induced in the cavity pressure by ventilating of the subject or breathing by the subject, the depth of anaesthesia of the subject may be readily monitored, thereby giving an advanced warning to an anaesthetist in the event of the depth of anaesthesia of the subject being reduced to a level at which the subject may begin to emerge from the anaesthetic prior to the procedure being carried out in the insufflated cavity being completed.

A further advantage of the invention is that the insufflators according to the invention avoid the risk of bradycardia, and also avoid the risk of a characteristic indicative of the performance of the heart of the subject falling below a predefined minimum value of the performance characteristic, or exceeding a predefined maximum value of the performance characteristic, during insufflating of the peritoneal cavity or other cavity of the subject being insufflated.

The invention will be more clearly understood from the following description of some preferred embodiments thereof which are given by way of example only with reference to the accompanying drawings, in which: Fig. 1 is a block representation of an insufflator according to the invention in use insufflating the peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 2 is another block representation of the insufflator of Fig. 1 also in use in insufflating the peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 3 is a block representation of an insufflator according to another embodiment of the invention in use in insufflating a peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 4 is a block representation of an insufflator according to a further embodiment of the invention in use in insufflating a peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 5 is a block representation of an insufflator according to another embodiment of the invention in use in insufflating a peritoneal cavity of a subject during a laparoscopic procedure,

Fig.6 is a block representation of an insufflator according to another embodiment of the invention in use in insufflating a peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 7 is a look-up table stored in memory of the insufflator of Fig. 6,

Fig. 8 is a block representation of an insufflator according to another embodiment of the invention in use in insufflating a peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 9 is a look-up table stored in memory of the insufflator of Fig. 8,

Fig. 10 is a block representation of an insufflator according to a further embodiment of the invention in use in insufflating a peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 11 is a block representation of an insufflator according to another embodiment of the invention in use in insufflating a peritoneal cavity of a subject during a laparoscopic procedure,

Fig. 12 is a representation of a waveform produced by the insufflator of Fig. 11 , Fig. 13 is a representation of another waveform produced by the insufflator of Fig. 11 , and

Fig. 14 is a representation of a further waveform produced by the insufflator of Fig. 11.

Referring to the drawings, and initially to Figs. 1 and 2 thereof, there is illustrated an insufflator according to the invention indicated generally by the reference numeral 1 , which in this embodiment of the invention is configured for insufflating the peritoneal cavity 2 of a human subject 3 during a minimally invasive laparoscopic procedure in the peritoneal cavity 2. The insufflator 1 is responsive to airway pressure and in particular to peak airway pressure in the airway 4 of the subject 3 exceeding a maximum safe airway pressure value, in this case a maximum safe peak' airway pressure value, for reducing the pressure in the peritoneal cavity 2 during insufflating thereof, in order to reduce upward movement into the thoracic cavity 5 of the diaphragm 6 separating the peritoneal cavity 2 from the thoracic cavity 5, which in turn results in an increase in the pressure on the lungs 7 of the subject. This increase in pressure on the lungs 7 of the subject 3 leads to an increase in the peak airway pressure in the airway 4 of the subject 3.

The laparoscopic procedure in the peritoneal cavity 2 is carried out through one or more trocars 8 extending into the cavity 2 of the subject 3 through the abdominal wall 9, as will be understood by those skilled in the art. The cavity 2 is insufflated by the insufflator 1 through a gas accommodating conduit 10 from the insufflator 1 connected to one of the trocars 8, for example, the trocar 8a, or extending into the cavity 2 through the trocar 8a. In this case, the gas accommodating conduit 10 is connected to an insufflating gas port 12 of the trocar 8a.

The insufflator 1 comprises a housing 15, and is suitable for connecting to an external pressurised source of insufflating gas 16, for example, an external pressurised source of carbon dioxide gas of the type typically available in a hospital operating theatre. The insufflator 1 is configured to control the flow and the flow rate of insufflating gas to the peritoneal cavity 2. A first inlet port 18 located in the housing 15 is provided for connecting the insufflator 1 to the external insufflating gas source 16. A flow controller 19 located in the housing 15 and connected to the first inlet port 18 controls the flow of insufflating gas from the external insufflating gas source 16, and delivers the insufflating gas at an appropriate flow rate to a first outlet port 20 located in the housing 15. The first outlet port 20 is adapted for connecting to the gas accommodating conduit 10 for accommodating insufflating gas to the trocar 8a.

A signal processor, in this embodiment of the invention comprising a microprocessor 25 located in the housing 15 controls the operation of the insufflator and controls the operation of the flow controller 19 for controlling both the supply of insufflating gas and the rate of flow of the insufflating gas through the first outlet port 20 to the peritoneal cavity 2. A cavity pressure monitoring means for monitoring the pressure in the peritoneal cavity 2 (cavity pressure), in this embodiment of the invention comprises a first pressure sensor 27 and a second pressure sensor 29 both of which are located in the housing 15, and both of which produce signals indicative of the cavity pressure, which is read by the microprocessor 25. The first pressure sensor 27 is connected to the first outlet port 20 for monitoring the pressure in the peritoneal cavity 2 through the gas accommodating conduit 10. The second pressure sensor 29 is connected to a pressure monitoring port 30 in the housing 15 for in turn connecting to a pressure monitoring conduit 31 for connecting to, either an insufflating gas port in another one of the trocars 8, for example, the trocar 8b, or in this case, for connecting to a Veress needle 32 extending through the abdominal wall 9 into the peritoneal cavity 2 for directly monitoring the cavity pressure in the cavity 2. If there is provision for connecting the pressure monitoring port 30 directly to the peritoneal cavity 2, as in the present case, the signal indicative of the cavity pressure is read continuously by the microprocessor 25 from the second pressure sensor 29.

However, if there is no provision for connecting the pressure monitoring port 30 directly to the peritoneal cavity 2, cavity pressure is read by the microprocessor 25 from the first pressure sensor 27 which monitors cavity pressure through the first outlet port 20, and in turn through the gas accommodating conduit 10. The cavity pressure is read by the microprocessor 25 from the first pressure sensor 27 at predefined time intervals typically of 1 to 2 seconds, and during reading of the pressure from the first pressure sensor 27, the flow controller 19 is operated by the microprocessor 25 to pause insufflating of the cavity 2 to allow the pressure in the conduit 10 adjacent the first outlet port 20 to settle at a pressure equal to the cavity pressure, so that the pressure read by the first pressure sensor 27 is equal to the cavity pressure.

A pressure reducing means for reducing the pressure in the peritoneal cavity 2 in this embodiment of the invention comprises a venting means, provided in this case by a venting valve 33 located in the housing 15. The venting valve 33 is connected to the first outlet port 20, and is operated under the control of the microprocessor 25, as will be described below, for venting insufflating gas from the peritoneal cavity 2 to reduce the cavity pressure.

A first receiving means for receiving a signal indicative of the peak airway pressure of the subject 3, in this embodiment of the invention comprises a first receiving port 34 located in the housing 15. The first receiving port 34 is configured to releasably receive a connector 35 of an electrically conductive wire 36 carrying an electronic signal indicative of the peak airway pressure of the subject 3 derived from an airway pressure monitoring means. The microprocessor 25 reads the signal indicative of the peak airway pressure of the subject 3 from the first receiving port 34. In this embodiment of the invention the airway pressure monitoring means comprises an airway pressure sensor 37 of an anaesthesia control and monitoring machine 38 which monitors the airway pressure of the subject, and produces the signal indicative of the peak airway pressure of the subject. The signal indicative of the peak airway pressure of the subject produced by the airway pressure sensor 37 is applied to the wire 36. Although in some embodiments of the invention the signal indicative of the peak airway pressure of the subject may be derived from a pressure sensor of a ventilator ventilating the subject, or the airway pressure of the subject may be monitored by a pressure sensor provided with the insufflator 1 and adapted for monitoring the airway pressure in a pressure line from a ventilator to an endotracheal tube ventilating the subject. Alternatively, the insufflator 1 may be provided with a pressure sensor located in the housing 15 which would be connected by a conduit to an endotracheal tube in the subject for monitoring the airway pressure of the subject. The microprocessor 25 would be programmed to read a signal from the pressure sensor indicative of the airway pressure of the subject and would be programmed to determine the peak airway pressure of the subject from the read signal. A conduit 39 connects the anaesthesia control and monitoring machine to a face mask 41 attached to the face of the subject covering the mouth and nose of the subject.

An interface, which in this embodiment of the invention comprises a touchscreen interface 40 located in a control panel (not shown) in the housing 15 of the insufflator 1 is provided for inputting data to the microprocessor 25, and for displaying data relative to the cavity pressure, the airway pressure and the peak airway pressure of the subject, and other relevant data relating to the insufflating of the peritoneal cavity 2 of the subject 3.

The maximum safe peak airway pressure value is stored in memory 42 of the microprocessor 25, and may be preset in the memory 42 or may be selectable. In this embodiment of the invention the maximum safe peak airway pressure value is selectable and is inputted into the memory 42 of the microprocessor 25 through the touchscreen interface 40.

A target pressure value at which the peritoneal cavity 2 is to be insufflated by the insufflator 1 is also stored in the memory 42 of the microprocessor 25, and may be preset or may be selectable. In this embodiment of the invention the target pressure value at which the peritoneal cavity 2 is to be insufflated is selectable and is entered into the memory 42 of the microprocessor 25 through the touchscreen interface 40.

A means for producing an aurally perceptible warning signal in this embodiment of the invention comprises a piezoelectric sounder 43 located in the insufflator 1 is operated under the control of the microprocessor 25 for producing an audible warning sound warning the surgeon or clinician to any problems described below which may occur during insufflating of the cavity 2 of the subject 3. A means for producing a visually perceptible signal comprises a warning light 44 located on the housing 15 of the insufflator 1 which is operated under the control of the microprocessor 25 to produce a visible warning signal, typical, by operating the warning light 44 to flash to warn a surgeon or clinician to any problem arising during insufflating of the cavity 2 of the subject 3, as will also be described below. To assist in a full understanding of the insufflator 1 and its operation, the operation of the insufflator 1 in the insufflating of the peritoneal cavity 2 of the subject 3 will now be described.

The first inlet port 18 of the insufflator 1 is connected to the external insufflating gas source 16, the connector 35 of the electrically conductive wire 36 from the pressure sensor 37 of the anaesthesia control and monitoring machine 38 is connected to the first receiving port 34, the first outlet port 20 is connected to the inlet port 12 of the trocar 8a through the gas accommodating conduit 10, and the pressure monitoring port 30 is connected to the Veress needle 32 by the pressure monitoring conduit 31. The target pressure value to which the peritoneal cavity 2 is to be insufflated is entered into the microprocessor 25 through the touchscreen interface 40 and is stored in the memory 42. The maximum safe peak airway pressure value is also entered into the microprocessor 25 through the touchscreen interface 40 and is stored in the memory 42.

During insufflating of the peritoneal cavity 2, the microprocessor 25 operates the flow controller 19 to supply insufflating gas to the peritoneal cavity 2 through the gas accommodating conduit 10. The microprocessor 25 substantially continuously reads the signal from the second pressure sensor 29 indicative of the cavity pressure, and operates the flow controller 19 in response to the signal read from the second pressure sensor 29 to maintain the pressure in the peritoneal cavity 2 at the target pressure value. In this embodiment of the invention the microprocessor 25 reads the signal from the second pressure sensor 29 at millisecond intervals, in this case, at predefined monitoring time intervals of approximately 10 milliseconds.

The microprocessor 25 during insufflating of the peritoneal cavity 2 also reads the signal on the first receiving port 34 received from the pressure sensor 37 of the anaesthesia control and monitoring machine 38 indicative of the peak airway pressure of the subject 3, and compares the read peak airway pressure of the subject with the maximum safe peak airway pressure value stored in the memory 42. If during initial insufflating of the cavity 2 to bring the cavity pressure up to the target pressure value or during insufflating of the cavity 2 at the target pressure value, the peak airway pressure of the subject 3 is at or below the maximum safe peak airway pressure value, the microprocessor 25 continues to operate the flow controller 19 to continue to bring the cavity pressure up to the target pressure value, and to maintain the cavity pressure at the target pressure value.

However, if the peak airway pressure of the subject 3 exceeds the maximum safe peak airway pressure value, at any time during insufflating of the peritoneal cavity 2, the microprocessor 25 operates the flow controller 19 to reduce the rate at which insufflating gas is being delivered to the cavity 2 or to pause delivery of insufflating gas to the cavity 2 in order to reduce the cavity pressure in incremental pressure reducing steps. The cavity pressure is reduced by an incremental pressure value in each incremental pressure reducing step. The incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step, may be the same for each incremental pressure reducing step, or the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step may be different to the pressure value by which the cavity pressure is reduced in the immediately previous incremental pressure reducing step. In this embodiment of the invention the incremental pressure value by which the cavity pressure is reduced during each incremental pressure reducing step is the same, and in this case is approximately 1mmHg. In other words, in each incremental pressure reducing step, the incremental pressure value by which the cavity pressure is reduced is approximately 1 mmHg.

Additionally, in this embodiment of the invention after the cavity pressure has been reduced by the incremental pressure value in each incremental pressure reducing step, the flow controller 19 is operated to maintain the cavity pressure substantially constant at the current reduced cavity pressure for a predefined dwell time interval, which in this embodiment of the invention is approximately 1 minute. If at the end of the current predefined dwell time interval the peak airway pressure of the subject 3 is at or below the maximum safe peak airway pressure value, the microprocessor 25 operates the flow controller 19 to delivery insufflating gas to the cavity 2 of the subject at a rate for maintaining the cavity pressure at the current now reduced cavity pressure.

While the predefined dwell time interval has been described as being approximately 1 minute, in some embodiments of the invention the predefined dwell time interval may range from 0.5 minutes to 2 minutes. Additionally, while the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step has been described as being 1mmHg, it is envisaged that the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step may lie in the range of 0.5mmHg to 2mmHg. The predefined dwell time interval and the incremental pressure value may be preset in the memory 42 or may be selectable, in this embodiment of the invention both the predefined dwell time interval and the incremental pressure value are selectable.

In order to reduce the cavity pressure during each incremental pressure reducing step, as discussed above, the microprocessor 25 may either reduce the rate at which insufflating gas is being delivered to the cavity 2 or operate the flow controller 19 to pause delivery of insufflating gas to the cavity 2, or the microprocessor 25 may operate the venting valve 33 to vent insufflating gas from the peritoneal cavity 2. If the flow controller 19 is delivering insufflating gas to the cavity at a relatively high rate in order to maintain the cavity pressure at the target pressure value, or at the current reduced cavity pressure, in general, it will be sufficient to operate the flow controller 19 to reduce the delivery rate of insufflating gas to the cavity or to pause delivery of insufflating gas to the cavity 2. However, if (he rate at which insufflating gas is being delivered to the cavity by the flow controller 19 is relatively low to maintain the cavity pressure at the target pressure value or the current reduced cavity pressure, then in order to reduce the cavity pressure by the incremental pressure value in each incremental pressure reducing step, it most likely will be necessary to operate the flow controller to pause delivery of insufflating gas to the cavity and to operate the venting valve 33 to vent insufflating gas from the cavity 2 in order to reduce the cavity pressure by the incremental pressure value.

If on the other hand at the end of the first one of the predefined dwell time intervals of 1 minute, or at the end of any subsequent predefined dwell time interval, the peak airway pressure of the subject has not been reduced to or below the maximum safe peak airway pressure value, the microprocessor 25 operates the flow controller 19 and/or the venting valve 33 to reduce the cavity pressure by a further one of the incremental pressure values in a further one of the incremental pressure reducing steps, and the microprocessor 25 operates the flow controller 19 to maintain the cavity pressure at the current reduced cavity pressure value for the predefined dwell time interval of 1 minute, and so on until the peak airway pressure of the subject has been reduced to or below the maximum safe peak airway pressure value. At which stage, the microprocessor 25 operates the flow controller 19 to maintain the cavity pressure at the now further reduced cavity pressure.

If, during the process of reducing the cavity pressure in any of the incremental pressure reducing steps, due to lack of leakage of insufflating gas from the peritoneal cavity 2, operating the flow controller 19 to pause delivery of insufflating gas to the peritoneal cavity 2 is insufficient to reduce the cavity pressure by the incremental pressure value, the microprocessor 25 operates the venting valve 33 to reduce the cavity pressure by each incremental pressure value.

If during the process of reducing the cavity pressure by the incremental pressure values in the incremental pressure reducing steps to in turn reduce the peak airway pressure of the subject to or below the maximum safe peak airway pressure value, the cavity pressure is reduced to a predefined minimum cavity pressure value before the peak airway pressure of the subject has been reduced to or below the maximum safe peak airway pressure value, the microprocessor 25 operates the flow controller 19 to maintain the cavity pressure at the predefined minimum cavity pressure value. The microprocessor 25 then operates the piezoelectric sounder 43 to produce an audible warning signal and operates the warning light 44 to flash to provide a visual warning, warning the surgeon or clinician that the cavity pressure has been reduced to the predefined minimum cavity pressure value, and the peak airway pressure of the subject is still above the maximum safe peak airway pressure value. The microprocessor 25 also outputs a signal to the touchscreen interface 40 to display a message alerting the surgeon or clinician to the fact that the cavity pressure has been reduced to the predefined minimum cavity pressure value and the peak airway pressure of the subject is above the maximum safe peak airway pressure value. The predefined minimum cavity pressure value is a pressure value consistent with providing a minimum working volume in the peritoneal cavity 2 of the subject 3. Typically the predefined minimum cavity pressure value lies in the range from 3mmHg to 8mmHg, and in general, the predefined minimum cavity pressure typically for a peritoneal cavity is approximately 5mmHg, although this will depend to some extent on the sex, age and body mass index of the subject.

The predefined minimum cavity pressure may be preset in the memory 42 of the microprocessor 25, or may be selectable. In this embodiment of the invention the predefined minimum cavity pressure is selectable by entering the selected value of the predefined minimum cavity pressure into the microprocessor 25 through the touchscreen interface 40 for storing in the memory 42.

It is also envisaged that in some embodiments of the invention the target pressure value for the cavity pressure may be set at a pressure equal to or just below the maximum safe peak airway pressure value, since it is believed that in some cases there may be a one-to-one relationship between the cavity pressure and the peak airway pressure of the subject, particularly, at cavity pressures over a certain value, which would result in the diaphragm between the peritoneal cavity and the thoracic cavity being urged into the thoracic cavity to the extent that it would bear on the lungs of the subject.

In use, with the first inlet port 18 of the insufflator 1 connected to the external insufflating gas source 16, the connector 35 of the electrically conductive wire 36 from the pressure sensor 37 of the anaesthesia control and monitoring machine 38 connected to the first receiving port 34, the first outlet port 20 connected to the inlet port 12 of the trocar 8a through the gas accommodating conduit 10 and the pressure monitoring port 30 connected to the Veress needle 32 by the pressure monitoring conduit 31, the insufflator 1 is ready for use. The target pressure value at which the peritoneal cavity 2 is to be insufflated is entered into the memory 42 of the microprocessor 25 through the touchscreen interface 40, the maximum safe peak airway pressure value is entered into the memory 42 of the microprocessor 25 through the touchscreen 40. The incremental pressure value by which the cavity pressure is to be reduced in each incremental pressure reducing step and the value of the predefined dwell time interval, as well as the predefined minimum cavity pressure value are also entered into the memory 42 of the microprocessor 25 through the touchscreen interface 40.

The insufflator 1 is then activated and the microprocessor 25 operates the flow controller 19 to deliver insufflating gas to the cavity 2 of the subject 3 in order to insufflate the cavity at the target pressure value. The microprocessor 25 reads signals from the second pressure sensor 29 and operates the flow controller 19 to raise the cavity pressure to the target pressure value and to maintain the cavity pressure at the target pressure value. The microprocessor 25 reads the signal on the first receiving port 34 from the pressure sensor 37 of the anaesthesia control and monitoring machine 38 and determines the peak airway pressure of the subject. For so long as the peak airway pressure of the subject remains at or below the maximum safe peak airway pressure value, the microprocessor 25 continues to operate the flow controller 19 to maintain the cavity pressure at the target pressure value.

In the event of the signal read from the pressure sensor 37 of the anaesthesia control and monitoring machine 38 exceeding the maximum safe peak airway pressure value, the microprocessor 25 operates the flow controller 19 to reduce or pause delivery of insufflating gas to the cavity 2, and if necessary, operates the venting valve 33 to vent insufflating gas from the peritoneal cavity 2 in order to reduce the cavity pressure by the incremental pressure value in a first one of the incremental cavity pressure reducing steps. When the cavity pressure has been reduced by the incremental pressure value in the first incremental pressure reducing step, the microprocessor 25 operates the flow controller 19 to maintain the cavity pressure constant at the current reduced cavity pressure value for the predefined dwell time interval. At the end of the predefined first dwell time interval, if the peak airway pressure of the subject has fallen to or is below the maximum safe peak airway pressure value, the microprocessor 25 operates the flow controller 19 to continue to insufflate the cavity at the current reduced cavity pressure value.

If the peak airway pressure at the end of the predefined first dwell time interval is still above the maximum safe peak airway pressure value, the microprocessor 25 operates the flow controller 19 and/or the venting valve 33 to reduce the cavity pressure by a further one of the incremental pressure values in a further incremental pressure reducing step, and the flow controller is operated by the microprocessor 25 to maintain the cavity pressure at the current reduced cavity pressure for the predefined dwell time interval, and so on until the peak airway pressure of the subject has fallen to or below the maximum safe peak airway pressure value.

However, if the cavity pressure has been reduced to the predefined minimum cavity pressure value before the peak airway pressure of the subject has been reduced to or below the maximum safe peak airway pressure value, the microprocessor 25 operates the flow controller 19 to maintain the cavity pressure at the predefined minimum cavity pressure value, and the microprocessor 25 operates the piezoelectric sounder 43 and the warning light 44 to produce a warning signal to a surgeon or clinician alerting to the fact that the cavity pressure is at the predefined minimum cavity pressure, and the peak airway pressure of the subject is still above the maximum safe cavity pressure value. The microprocessor 25 also outputs a signal to the touchscreen interface 40 also drawing attention to the fact that the cavity pressure is currently at the predefined minimum cavity pressure value, and the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value. At that stage, the surgeon or clinician carrying out the procedure makes a decision as to how to proceed with the procedure and the insufflating or otherwise of the cavity of the subject. Referring now to Fig. 3 there is illustrated an insufflator according to another embodiment of the invention indicated generally by the reference numeral 50. The insufflator 50 in this embodiment of the invention is configured to insufflate the peritoneal cavity 2 of a subject 3 and is responsive to the peak airway pressure of the subject exceeding a maximum safe peak airway pressure value for reducing the pressure in the peritoneal cavity 2 during insufflating thereof, in order to reduce upward movement of the diaphragm between the peritoneal cavity 2 and the thoracic cavity into the thoracic cavity. Neither the thoracic cavity nor the diaphragm separating the thoracic cavity from the peritoneal cavity 2 are shown in this embodiment of the invention. The insufflator 50 is substantially similar to the insufflator 1, and similar components are identified by the same reference numerals. The main difference between the insufflator 50 and the insufflator 1 is that instead of providing the pressure reducing means for reducing the cavity pressure as a venting valve, the pressure ' reducing means in this embodiment of the invention comprises a means for applying a vacuum to the peritoneal cavity 2. The vacuum is derived from an external vacuum source 52, typically, from an external vacuum source of the type available in a hospital operating theatre.

A second inlet port 54 is located in the housing 15 and is adapted for connecting the insufflator 50 to the external vacuum source 52. In this embodiment of the invention the means for applying the vacuum to the peritoneal cavity 2 comprises a communicating means, namely, an isolating valve 55 located in the housing 15 and connected between the second inlet port 54 and the first outlet port 20. The isolating valve 55 is operated under the control of the microprocessor 25 between an isolating state isolating the first outlet port 20 from the second inlet port 54, and a communicating state communicating the first outlet port 20 with the second inlet port 54, for in turn applying the vacuum to the first outlet port 20, and in turn to the peritoneal cavity 2 for reducing the cavity pressure therein.

In this embodiment of the invention the microprocessor 25 is responsive to the peak airway pressure of the subject 3 exceeding the maximum safe peak airway pressure value for operating the flow controller 19 to reduce the delivery rate of insufflating gas to the cavity 2, to pause delivery of insufflating gas to the cavity 2, or to operate the isolating valve 55 from the isolating state to the communicating state for applying the vacuum to the peritoneal cavity 2 through the first outlet port 20 to withdraw insufflating gas from the peritoneal cavity 2, and to in turn reduce the pressure in the peritoneal cavity 2. The microprocessor 25 is programmed to operate the flow controller 19 and/or the isolating valve 55 in a similar manner as the microprocessor 25 of the insufflator 1 operates the flow controller 19 and the venting valve 33 for reducing the cavity pressure in the peritoneal cavity 2, for in turn maintaining the peak airway pressure of the subject at or below the maximum safe peak airway pressure value. In other words, if the rate of delivery of insufflating gas to the cavity 2 is relatively high, in order to maintain the cavity pressure at the target pressure value, then to reduce the cavity pressure by the incremental pressure value during each incremental pressure reducing step, it may be sufficient to operate the flow controller 19 to either reduce rate of delivery of insufflating gas to the cavity or to pause the delivery of insufflating gas to the cavity, without the need to operate the isolating valve 55 from the isolating state to the communicating state in order to apply vacuum to the cavity 2.

However, in cases where the rate of delivery of insufflating gas to the cavity in order to maintain the cavity pressure at the target cavity pressure is relatively low, then in order to reduce the cavity pressure by the incremental pressure value during each incremental pressure reducing step, it most likely will be necessary to operate the flow controller 19 to pause delivery of insufflating gas to the cavity and to operate the isolating valve 55 from the isolating state to the communicating state in order to apply vacuum to the cavity 2 for withdrawing insufflating gas therefrom.

In this embodiment of the invention the second pressure sensor 29 is connected through the pressure monitoring port 30 directly to the peritoneal cavity 2, the pressure monitoring conduit 31, and through the Veress needle 32 in a similar manner as the second pressure sensor 29 of the insufflator 1 is connected to the peritoneal cavity 2, as described with reference to Figs. 1 and 2. Accordingly, in this embodiment of the invention since the second pressure sensor 29 is connected through the pressure monitoring port 30 directly to the peritoneal cavity 2, the cavity pressure is substantially continuously monitored by the microprocessor 25 from the signal produced by the second pressure sensor 29 of the insufflator as already described with reference to Figs. 1 and 2.

However, it will be readily apparent to those skilled in the art that the microprocessor 25 may be programmed to monitor the pressure in the peritoneal cavity 2 from the signal read from the first pressure sensor 27. In which case, each time the microprocessor 25 is to read the signal from the first pressure sensor 27, the microprocessor 25 would operate the flow controller 19 to pause the supply of insufflating gas to the peritoneal cavity 2, in order to allow the pressure at the first outlet port 20 to settle at the cavity pressure, so that the signal read from the first pressure sensor 27 would be indicative of the cavity pressure as described with reference to the insufflator 1 described with reference to Figs. 1 and 2.

Additionally, during the application of the vacuum to the peritoneal cavity 2, if the microprocessor 25 is monitoring the cavity pressure from the first pressure sensor 27, each time the signal produced by the first pressure sensor 27 is being read by the microprocessor 25, the microprocessor 25 would operate the isolating valve 55 into the isolating state, so that the signal read from the first pressure sensor 27 would be indicative of the pressure in the peritoneal cavity 2.

Otherwise, the insufflator 50, its operation and use are similar to that of the insufflator 1 described with reference to Figs. 1 and 2.

Referring now to Fig. 4 there is illustrated an insufflator according to another embodiment of the invention indicated generally by the reference numeral 60 for insufflating a peritoneal cavity 2 of a subject 3. The insufflator 60 is configured to be responsive to the peak airway pressure of the subject exceeding a maximum safe peak airway pressure value for reducing the pressure in the peritoneal cavity 2 during insufflating thereof in order to reduce upward movement into the thoracic cavity of the diaphragm between the peritoneal cavity 2 and the thoracic cavity. Neither the thoracic cavity nor the diaphragm separating the thoracic cavity from the peritoneal cavity are shown in this embodiment of the invention.

The insufflator 60 is substantially similar to the insufflator 50 described with reference to Fig. 3, and similar components are identified by the same reference numerals. The main difference between the insufflator 60 and the insufflator 50 is that the isolating valve 55 is connected between the second inlet port 54 and a second outlet port 62 located in the housing 15. The second outlet port 62 is adapted for connecting directly to the peritoneal cavity 2 through a vacuum accommodating conduit 64, which in this embodiment of the invention is connected to a gas inlet port 65 of the second trocar 8b. Additionally, in this embodiment of the invention the second pressure sensor 29 is connected through the pressure monitoring port 30 directly to the peritoneal cavity 2 through the pressure monitoring conduit 31 and the Veress needle 32.

Otherwise, operation of the insufflator 60 and its use and operation are similar to that already described with reference to the insufflator 50.

Referring now to Fig. 5 there is illustrated an insufflator according to another embodiment of the invention indicated generally by the reference numeral 70. The insufflator 70 is also configured for insufflating the peritoneal cavity 2 of a human subject 3 during a minimally invasive laparoscopic procedure. Like the insufflators 1, 50 and 60 described with reference to Figs. 1 to 4, the insufflator 70 is responsive to the peak airway pressure in the airway of the subject 3 exceeding a maximum safe peak airway pressure value for reducing the pressure in the peritoneal cavity 2 during insufflating thereof, in order to reduce upward movement into the thoracic cavity of the diaphragm separating the thoracic cavity from the peritoneal cavity 2. The insufflator 70 is substantially similar to the insufflator 1 , and similar components are identified by the same reference numerals.

The main difference between the insufflator 70 and the insufflator 1 is firstly, that instead of providing the pressure reducing means for reducing the pressure in the cavity 2 as a venting valve for venting insufflating gas from the peritoneal cavity 2 of the subject 3, the pressure reducing means comprises a vacuum pump 71, and secondly, instead of providing the first receiving means for receiving the signal indicative of the peak airway pressure of the subject as a first receiving port, the first receiving means comprises a first wireless receiver 72 for receiving the signal indicative of the peak airway pressure of the subject 3 wirelessly from the anaesthesia control and monitoring machine 38. Turning initially to the vacuum pump 71, the vacuum pump 71 is located in the housing 15 of the insufflator 70, for applying a vacuum to the peritoneal cavity 2 of the subject 3 for drawing insufflating gas from the peritoneal cavity 2 in order to reduce the pressure in the cavity 2. The vacuum pump 71 is connected to the first outlet port 20 in a similar manner as the venting valve of the insufflator 1 is connected to the first outlet port 20. The flow controller 19 and the vacuum pump 71 are operated under the control of the microprocessor 25 in a similar manner as the flow controller 19 and the venting valve 33 of the insufflator 1 are operated under the control of the microprocessor 25 for controlling the pressure in the peritoneal cavity 2 of the subject 3 for maintaining the peak airway pressure of the subject at or below the maximum safe peak airway pressure value.

However, it will be appreciated that the vacuum pump 71 may be connected to the peritoneal cavity of the subject 3 in a similar manner as the isolating valve 55 of the insufflator 60 of Fig. 4 is connected to the peritoneal cavity 2 of the subject 3, whereby the vacuum pump 71 would be connected through a second outlet port similar to the second outlet port 62 of the insufflator 60, and in turn through the vacuum accommodating conduit 64 to the insufflating gas inlet port 65 of the trocar 8b as illustrated in Fig. 4.

Turning now to the first wireless receiver 72, the first wireless receiver 72 is located in the housing 15 for wirelessly receiving the signal from the pressure sensor 37 of the anaesthesia control and monitoring machine 38 indicative of the peak airway pressure of the subject. The signal indicative of the peak airway pressure of the subject is transmitted by a wireless transmitter 73 located in the anaesthesia control and monitoring machine 38 from the pressure sensor 37 thereof. The wireless transmitter 73 and the first wireless receiver 72 are configured to transmit and receive the signal indicative of the peak airway pressure of the subject by Bluetooth protocol or other suitable near field communication protocol. The microprocessor 25 continuously reads the signal indicative of the peak airway pressure of the subject received by the first wireless receiver 72.

Otherwise, the insufflator 70, its operation and use are similar to that of the insufflator 1 described with reference to Figs. 1 and 2.

Referring now to Figs. 6 and 7 there is illustrated an insufflator according to another embodiment of the invention indicated generally by the reference numeral 75 for insufflating the peritoneal cavity 2 of a human subject 3 or a cavity in an organ in the peritoneal cavity. The insufflator 75 is responsive to the peak airway pressure of the subject 3 exceeding a maximum safe peak airway pressure value for reducing the pressure in the peritoneal cavity 2, or other cavity in the peritoneal cavity 2 during insufflating thereof, in order to reduce upward movement into the thoracic cavity of the diaphragm separating the thoracic cavity from the peritoneal cavity 2. Additionally, the insufflator 75 is configured for controlling the rate of insufflating of the peritoneal cavity 2, or other cavities in the peritoneal cavity 2 in the body of the subject 3 so that the rate of insufflating of the peritoneal cavity 2 or other cavity therein is maintained below a maximum insufflating rate value which would lead to the occurrence of bradycardia where the heart rate of the subject reduces to a dangerously low heart rate value.

The insufflator 75 is substantially similar to the insufflator 1 described with reference to Figs. 1 and 2, and similar components are identified by the same reference numerals. The operation of the insufflator 75 for controlling the pressure in the peritoneal cavity 2 or other cavity therein of the subject 3 in response to the peak airway pressure of the subject, in order to reduce the upward movement of the diaphragm separating the thoracic cavity from the peritoneal cavity 2 into the thoracic cavity, is similar to that described with reference to the insufflator 1.

The use and operation of the insufflator 1 in order to control the rate of insufflating of the cavity 2 to avoid the occurrence of bradycardia in the subject, will now be described, but for ease of understanding this aspect of the invention will only be described for insufflating the peritoneal cavity 2. In this embodiment of the invention as well as the electronic memory 42 of the microprocessor 25 storing the target pressure value at which the cavity 2 is to be insufflated, the maximum safe peak airway pressure value, the incremental pressure value, the predefined dwell time interval and the predefined minimum cavity pressure value, the memory 42 of the microprocessor 25 also stores a plurality of maximum insufflating rate values over which the rate of insufflating of the peritoneal cavity should not exceed in order to avoid the occurrence of bradycardia.

It has been found that the maximum insufflating rate at which the peritoneal cavity 2 and other cavities in the peritoneal cavity 2 may be insufflated in order to avoid bradycardia depends largely on the compliability of the abdominal wall of the peritoneal cavity of the subject and the diaphragm separating the thoracic cavity from the peritoneal cavity, and other compliant aspects of the peritoneal cavity. The compliance of the peritoneal cavity is dependent on the age of the subject, the body mass index of the subject, and also the compliance of the peritoneal cavity varies between male and female subjects. Accordingly, in this embodiment of the invention a plurality of maximum insufflating rate values for the peritoneal cavity are stored in the electronic memory 42 of the microprocessor 25 for both male and female subjects of different age ranges and different body mass indices. In this embodiment of the invention the maximum insufflating rate values are stored as a function of cavity pressure, and in this case are stored as the maximum increase in cavity pressure per second for the different types of subjects, and are stored in the memory 42 in the form of a look-up table 76 as illustrated in Fig. 7. Referring now to Fig. 7, the look-up table 76 stores the maximum increase in pressure per second for the peritoneal cavity in order to avoid bradycardia, for a male of different age ranges and different body mass indices. In column 1 of the look-up table 76, the cavity of subjects for which the maximum insufflating rate values are stored is set out, in this case the peritoneal cavity. Column 2 sets out the sex of the subject, namely, male subjects. Column 3 sets out the age ranges of the subject. In column 3, seven age ranges are set forth, namely, age range 1 to age range 7. Age range 1 is for male subjects of age zero years to 5 years of age. Age range 2 is for male subjects of age 6 years to 10 years, age range 3 is for male subjects of age 11 years to 15 years, age range 4 is for male subjects of age 16 years to 20 years, age range 5 is for male subjects of age 21 years to 40 years, age range 6 is for male subjects of age 41 years to 60 years, while age range 7 is for male subjects of age 61 years and greater.

Column 4 sets out three body mass index ranges against each of the seven age ranges of column 3. Body mass index range 1 includes body mass indices of male subjects of normal healthy weight within the relevant age ranges, namely, body mass indices in the range of 18.5 to 24.9. Body mass index range 2 includes body mass indices of underweight male subjects, namely, body mass indices below 18.6. Body mass index range 3 includes body mass indices of overweight, obese and morbidly obese male subjects, namely, body mass indices in the range of 25 to 40 and over. However, it is envisaged that in some embodiments of the invention more than three body mass index ranges may be provided, in particular, for subjects of age 21 and upwards. In which case, it is envisaged that the body mass index range 3 may be subdivided into three further body mass index ranges whereby one of the subdivisions of body mass index range 3 would include body mass indices for an overweight male subject but not an obese male subject whereby the body mass indices of that range would be between 25 and 29.9. A second subdivision of body mass index range 3 would include body mass indices of an obese male subject, and would include body mass indices in the range of 30 to 39.9. A third subdivision of the body mass index range 3 would include body mass indices of a morbidly obese male subject, namely, body mass indices of 40 and over.

It is also envisaged that in the case of subjects under the age of 15, instead of providing body mass index ranges, weight ranges may be provided whereby one weight range would be a normal weight range for such subjects within the relevant age range, a second weight range would be for underweight subjects of the relevant age range, while a third weight range would be a weight range for overweight, and possibly, obese subjects of the relevant age range.

Column 5 sets forth the maximum insufflating rate values, in this case the maximum values of the increase in cavity pressure per second, above which the increase in pressure per second in the peritoneal cavity 2 of the subject 3 should not be exceeded during insufflating thereof in the case of a male subject within corresponding age ranges, and within corresponding body mass index ranges. The maximum insufflating rate values in column 5 of the look-up table 76 are given as values APi per second to AP21 per second, in other words, the increase in cavity pressure per second.

It should be understood that the values of APi per second to AP21 per second do not progressively increase from APi to AP21, nor do they regressively decrease from APi to AP₂₍, the designations APi to AP21 are merely used to indicate different values of the maximum insufflating rate values. Since the peritoneal cavity of a person of relatively low body mass index will be more compliant than the peritoneal cavity of a person of the same sex and age of a relatively high body mass index, the cavity pressure will rise quicker in a person of higher body mass index than in a person of lower body mass index, and therefore the maximum insufflating rate value of AP per second will in general be lower for a person of high body mass index than that for a person of low body mass index, in order that the insufflating rate of a person of high body mass index is maintained at a slower insufflating rate than that for a person of low body mass index.

A look-up table (not shown) of a similar type to that of the look-up table 76 is stored in the memory 42 for female subjects. Additionally, look-up tables for male and female subjects similar to the look-up table 76 may also be stored in the memory 42 for other cavities in vessels and organs in the peritoneal cavity.

In order to assist in an understanding of the invention, the use of the insufflator 75 in insufflating the peritoneal cavity 2 of the subject 3 will now be described. Prior to commencing insufflating of the cavity 2 of the subject, as well as entering the target pressure value to which the cavity 2 is to be insufflated, the maximum safe peak airway pressure value for the subject, the incremental pressure value, the predefined dwell time interval value and the predefined minimum cavity pressure value, into the microprocessor 25 through the touchscreen interface 40, data relating to the type of the cavity of the subject to be insufflated, the sex, the age and the body mass index of the subject are entered into the microprocessor 25 through the touchscreen interface 40 and are stored in the memory 42. In this case the identity of the cavity to be insufflated is entered as the peritoneal cavity. With this data entered into the microprocessor 25, the microprocessor 25 selects the appropriate maximum increase in the cavity pressure per second, above which the peritoneal cavity 2 of the subject should not be insufflated, from column 5 of the look-up table 76 based on the entered sex, age and body mass index of the subject. The selected appropriate value of the maximum increase in cavity pressure per second is then stored by the microprocessor 25 in the memory 42 for the duration of the procedure during which the peritoneal cavity 2 of the subject 3 is being insufflated.

On activation of the insufflator 75, the microprocessor 25 then operates the flow controller 19 to deliver the insufflating gas to the cavity 2, and the microprocessor 25 reads the signal indicative of cavity pressure from the second pressure sensor 29. The microprocessor 25 operates the flow controller 19 to raise the cavity pressure to the target pressure value and then to maintain the cavity pressure at the target pressure value. The microprocessor 25 also reads the signal indicative of the peak airway pressure from the first receiving port 34.

Each time the cavity pressure is read from the pressure sensor 29, the microprocessor 25 computes the rate of increase of cavity pressure per unit time from the currently read value of the cavity pressure and the previously read value of the cavity pressure. The microprocessor 25 then compares the just computed value of the increase in cavity pressure per second with the stored value of the maximum increase in the cavity pressure per second. For so long as the computed values of the increase of cavity pressure per second does not exceed the stored value of the maximum increase in the cavity pressure per second, the microprocessor 25 operates the flow controller 19 to continue insufflating the cavity at the current rate at which the cavity is being insufflated to raise the cavity pressure to the target pressure value and maintain the cavity pressure at the target pressure value, or in the event that due to the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value the peritoneal cavity 2 is being insufflated to a cavity pressure value below the target pressure value, the microprocessor 25 operates the flow controller to continue insufflating the cavity 2 at the current rate at which the cavity is being insufflated.

In the event of the computed value of the increase in the cavity pressure per second exceeding the stored value of the maximum increase in cavity pressure per second, the microprocessor 25 operates the flow controller 19 to reduce the rate of delivery of insufflating gas to the cavity 2, in order to reduce the increase in the cavity pressure per second to a value below the stored value of the maximum increase in cavity pressure per second.

As already described, as well as the microprocessor 25 reading the signal from the second pressure sensor 29, the microprocessor 25 reads the signal on the first receiving port 34 indicative of the peak airway pressure of the subject 3. The microprocessor 25 also operates the flow controller 19 and/or the venting valve 33 for maintaining the peak airway pressure of the subject at or below the maximum safe peak airway pressure value in a similar manner as the microprocessor 25 controls the flow controller 19 and/or the venting valve 33 of the insufflator 1 described with reference to Figs. 1 and 2, for maintaining the peak airway pressure of the subject at or below the maximum safe peak airway pressure value.

Referring now to Figs. 8 and 9 there is illustrated an insufflator according to another embodiment of the invention indicated generally by the reference numeral 80 for insufflating the peritoneal cavity 2 in the body of a human subject 3. The insufflator 80 is substantially similar to the insufflator 75 and similar components are identified by the same reference numerals. The operation of the insufflator 80 for monitoring the airway pressure of the subject 3, and controlling the cavity pressure in the peritoneal cavity 2 in order to avoid the peak airway pressure of the subject 3 exceeding the maximum safe peak airway pressure value is similar to that described with reference to the insufflator 1 of Figs. 1 and 2. The operation of the insufflator 80 for maintaining the rate of insufflating of the peritoneal cavity 2 below an appropriate maximum insufflating rate value is also substantially similar to the operation of the insufflator 75 described with reference to Figs. 6 and 7.

The main difference between the insufflator 80 and the insufflator 75, is in the manner in which the values of the maximum insufflating rates for the respective different subjects are stored, and in the manner in which the microprocessor 25 is programmed to determine the rate of insufflating of the peritoneal cavity 2. In this embodiment of the invention instead of the maximum insufflating rate values being stored as the values of the maximum increase in cavity pressure per second, the maximum insufflating rate values are stored as functions of flow of insufflating gas to the cavity, and in this case are stored as the maximum flow rates of insufflating gas to the cavity. The microprocessor 25 is programmed to determine the rate of insufflating of the peritoneal cavity 2 as the flow rate of the insufflating gas being delivered to the peritoneal cavity 2, as will be described below.

A look-up table 81 in a format substantially similar to that of the look-up table 76 of Fig. 7 is stored in the memory 42. Columns 1 to 4 of the look-up table 81 are substantially similar to columns 1 to 4 of the look-up table 76. However, in column 5 of the look-up table 81 in this embodiment of the invention the values of the maximum insufflating rate for insufflating the peritoneal cavity 2 are stored as maximum flow rate values in litres per minute of the delivery of insufflating gas to the peritoneal cavity 2, above which the flow rates of insufflating gas to the peritoneal cavity 2 should not exceed, in order to avoid any risk of bradycardia, hypotension or cardiac arrest in the subject. The maximum flow rate values of insufflating gas to the peritoneal cavity are set out in column 5 of the look-up table 81 as the values F₁ litres per minute to F₂₁ litres per minute. The maximum flow rate values F₁ to F₂₁ of the rate of delivery of insufflating gas to the cavity are given in the look-up table 81 for the peritoneal cavity 2 for male subjects of seven different age ranges, similar to the seven age ranges of the look-up table 76 of Fig. 7, and of three different body mass index ranges similar to the three different body mass index ranges of the look-up table 76 of Fig. 7.

Although not illustrated, a separate look-up table, similar to the look-up table 81 , is stored in the memory 42 for the peritoneal cavity for female subjects of seven different age ranges, similar to the seven age ranges of the look-up table 76 of Fig. 7 and of three different body mass index ranges similar to the three different body mass index ranges of the look-up table 76 of Fig. 7.

It should be understood that the values of F₁ to F₂₁ of the maximum flow rates in litres per minute of insufflating gas delivered to the peritoneal cavity do not progressively increase from F₁ to F₂₁ , nor do they regressively decrease from F₁ to F₂₁ , the designations F₁ to F₂₁ are merely used to indicate different values of the maximum flow rate values of the delivery of insufflating gas to the peritoneal cavity. In general, since the peritoneal cavity of a person of relatively low body mass index will be more compliant than the peritoneal cavity of a person of the same sex and age of a relatively high body mass index, the maximum insufflating rate value of F litres per minute will in general be higher for such a person of low body mass index that that of such a person of the same age and sex of a higher body mass index. Furthermore, since the peritoneal cavity of a person of a relatively low age, for example, a person in the age range 1 or age range 2, will in general be more compliant than a person of the same sex of age in a higher one of the age ranges, for example, the age range 6 or the age range 7, the maximum insufflating rate value F litres per minute for a person of low body mass index of a low age, will in general be higher than a person of low body mass index of a higher age range. Therefore, in general, it is envisaged that while the maximum insufflating rate value of F litres per minute may decrease for a male in age range 1 from body mass index 1 to body mass index 3, and while the maximum insufflating rate value of F litres per minute for a male of age range 2 may decrease from body mass index 1 to body mass index 3, the value of F4 litres per minute typically, would be higher than the value of F₃ litres per minute.

A flow sensor 82 is located in the housing 15 between the flow controller 19 and the outlet port 20. The flow sensor 82 monitors the flow of insufflating gas to the peritoneal cavity 2 and produces a signal indicative of the flow rate of the insufflating gas to the peritoneal cavity 2. The microprocessor 25 reads the signal from the flow sensor 82, and compares the flow rate of the insufflating gas being delivered to the peritoneal cavity 2 with the appropriate stored value of the maximum flow rate of F litres per minute of insufflating gas to the peritoneal cavity 2 from the look-up table 81. If the flow rate read from the signal from the flow sensor 82 exceeds the stored selected appropriate value F litres per minute of the maximum flow rate of insufflating gas to the peritoneal cavity 2, the microprocessor 25 operates the flow controller 19 to reduce the flow rate of insufflating gas to the cavity until the flow rate of insufflating gas to the peritoneal cavity 2 falls to or below the appropriate stored value F litres per minute of the maximum flow rate of insufflating gas to the cavity.

The operation of the flow controller 19 by the microprocessor 25 in maintaining the cavity pressure at the target pressure value is similar to that described with reference to the insufflator 1 described with reference to Figs. 1 and 2 and the operation of the insufflator 80 in controlling the cavity pressure in order to maintain the peak airway pressure of the subject 3 at or below the maximum safe peak airway pressure value is similar to that described with reference to the insufflator 1 of Figs. 1 and 2.

Otherwise, the insufflator 80 and its use and operation are similar to the insufflator 75 and its operation.

Referring now to Fig. 10 there is illustrated an insufflator according to another embodiment of the invention indicated generally by the reference numeral 85 for insufflating a cavity, in this case the peritoneal cavity 2 in the body of a human subject 3. The insufflator 85 is substantially similar to the insufflator 75 described with reference to Figs. 6 and 7, and similar components are identified by the same reference numerals. The insufflator 85 like the insufflator 75 maintains the cavity pressure of the peritoneal cavity 2 at the target pressure value during insufflating of the peritoneal cavity 2, unless the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value as described with reference to the insufflator 1 of Figs. 1 and 2, at which stage the cavity pressure is reduced in the incremental pressure reducing steps in order to reduce the peak airway pressure of the subject 3 to or below the maximum safe peak airway pressure value. The insufflator 85 like the insufflator 75 also controls insufflating of the peritoneal cavity so that the increase in cavity pressure per unit time does not exceed the appropriate value of the maximum increase in cavity pressure per unit time based on the sex, age and body mass index of the subject. Accordingly, look-up tables setting forth predefined maximum values of the increase in cavity pressure per second in the peritoneal cavity for male and female subjects of different age ranges, and different body mass index ranges similar to (he look-up table of Fig. 7 are stored in the memory 42.

However, in this embodiment of the invention the insufflator 85 is also adapted to control insufflating of the peritoneal cavity 2, so that a characteristic indicative of the performance of the heart of the subject 3 does not exceed a predefined maximum value of the characteristic, and does not fall below a predefined minimum value of the characteristic. In this embodiment of the invention the insufflator 85 is adapted to control insufflating of the peritoneal cavity 2, so that the characteristic indicative of the performance of the heart of the subject, which in this case is the heart rate of the subject, does not exceed a predefined maximum heart rate value, or does not fall below a predefined minimum heart rate value.

The predefined maximum heart rate value and the predefined minimum heart rate value are stored in the memory 42, and may be preset or selectable. In this case the predefined maximum heart rate value and the predefined minimum heart rate value are selectable. The microprocessor 25 as will be described below, is programmed to monitor the heart rate of the subject 3, as will be described below, and to compare the monitored heart rate of the subject 3 with the predefined maximum heart rate value and the predefined minimum heart rate value.

However, it will be appreciated that while in this embodiment of the invention the heart rate of the subject is compared with the predefined maximum heart rate value and the predefined minimum heart rate value, since it is more critical that the heart rate or other characteristic indicative of the performance of the heart of the subject does not fall below a predefined minimum value of the characteristic, it is envisaged that in some embodiments of the invention the characteristic indicative of the performance of the heart of the subject may be compared only with a predefined minimum value of the characteristic, and in which case only the predefined minimum value of the characteristic, namely, the predefined minimum heart rate value, would be stored in memory.

As mentioned above, the insufflator 85 is substantially similar to the insufflator 75, however, in this embodiment of the invention the venting valve 33 is replaced with an isolating valve 55 similar to the isolating valve 55 of the insufflator of Fig. 3. The isolating valve 55 of the insufflator 85 is coupled to an external vacuum source 52 through a second inlet port 54. The isolating valve is connected to the first outlet port 20 for selectively applying vacuum from the external vacuum source 52 to the cavity 2 for drawing insufflating gas from the cavity 2 in order to reduce the cavity pressure, as described with reference to Fig. 3.

A second receiving means comprising a second receiving port 87 is located in the housing 15 for receiving a signal indicative of the heart rate of the subject 3.

A monitoring means for monitoring the characteristic indicative of the performance of the heart of the subject, in this case is provided by a heart rate monitor 88 for monitoring the heart rate of the subject 3. The heart rate monitor 88 may be any suitable heart rate monitor which produces an electronic signal indicative of the heart rate of the subject. The signal produced by the heart rate monitor is applied to the second receiving port 87 through an electrically conductive wire 89 connected to the second receiving port 87 by a connector 90. The microprocessor 25 reads the signal indicative of the heart rate of the subject applied to the second receiving port 87. The heart rate monitor 87 may be provided with the insufflator 85 for appropriately attaching to the subject to monitor the heart rate of the subject, or the signal indicative of the heart rate of the subject may be derived from any other suitable heart rate monitor attached to the subject during the procedure.

The microprocessor 25 is programmed to read the signal indicative of the heart rate of the subject applied to the second receiving port 87 substantially continuously at millisecond intervals, typically, at 10 millisecond intervals. Each time the signal is read from the second receiving port 87, the microprocessor 25 is programmed to compare the heart rate value of the read signal with the predefined maximum heart rate value and the predefined minimum heart rate value stored in the memory 42. If the read heart rate value of the subject 3 exceeds the predefined maximum heart rate value or falls below the predefined minimum heart rate value, the microprocessor 25 is programmed to operate the flow controller 19 to isolate the first outlet port 20 from the insufflating gas source 16 in order to terminate delivery of insufflating gas to the peritoneal cavity 2. Simultaneously, the microprocessor 25 is programmed to commence to time a predefined first delay time period, and operates the sounder 43 and the warning light 44 to produce an alert or a caution signal alerting to the fact that the heart rate of the subject has exceeded the predefined maximum heart rate value or has fallen below the predefined minimum heart rate value. In this embodiment of the invention the predefined first delay time period is approximately 30 seconds. During the predefined first delay time period, the microprocessor 25 is programmed to continue to read the signal indicative of the heart rate of the subject 3 applied to the second receiving port 87, and to compare each read signal with the predefined maximum and minimum heart rate values.

If at the end of the predefined first delay time period the heart rate of the subject has not returned within the predefined maximum heart rate value and the predefined minimum heart rate value and the cavity pressure exceeds the predefined minimum cavity pressure value, which is the minimum cavity pressure value consistent with maintaining a minimum working volume in the cavity 2, the microprocessor 25 operates the isolating valve 55 from the isolating state to the communicating state to apply vacuum to the peritoneal cavity 2 in order to draw insufflating gas from the peritoneal cavity 2 to further reduce the cavity pressure to the predefined minimum cavity pressure value. The predefined minimum cavity pressure value is as described in the insufflator 1 described with reference to Figs. 1 and 2. On the cavity pressure being reduced to the predefined minimum cavity pressure value, the microprocessor 25 is programmed to commence timing a predefined second delay time period, which in this embodiment of the invention is also approximately 30 seconds duration. During the predefined second delay time period, the microprocessor 25 is programmed to read the signal from the second receiving port 87 indicative of the heart rate of the subject.

At the end of the predefined second delay time period, if the heart rate of the subject has not returned within the predefined maximum heart rate value and the predefined minimum heart rate value, the microprocessor 25 is programmed to operate to the sounder 43 and the warning light 44 to produce a warning signal indicating that the cavity pressure has been reduced to the predefined minimum cavity pressure value and the heart rate of the subject is either still below the predefined minimum heart rate value or above the predefined maximum heart rate value.

The microprocessor 25 is also programmed to output a data signal to the touchscreen interface 40 to display a message indicative as appropriate, indicating that the heart rate of the subject is still either above the predefined maximum heart rate value or below the predefined minimum heart rate value, and the cavity pressure is at the predefined minimum cavity pressure value. This message would include particulars of the heart rate of the subject and the cavity pressure. At that stage, the surgeon or clinician then takes control of the insufflator to either terminate insufflating of the cavity 2 or to further reduce the cavity pressure below the predefined minimum cavity pressure value.

If during either the predefined first delay time period or the predefined second delay time period the heart rate of the subject returns within the predefined maximum heart rate value and the predefined minimum heart rate value, the microprocessor 25 is programmed to operate the flow controller 19 to recommence insufflating of the cavity at the reduced cavity pressure corresponding to the cavity pressure at which the heart rate of the subject 3 returned within the predefined maximum heart rate value and the predefined minimum heart rate value.

When the isolating valve 55 is being operated to reduce the cavity pressure in response to the heart rate of the subject exceeding the predefined maximum heart rate value or falling below the predefined minimum heart rate value, the isolating valve 55 is operated to reduce the cavity pressure as quickly as possible to the predefined minimum cavity pressure value consistent with maintaining a minimum working volume in the peritoneal cavity.

Prior to commencing insufflating of the cavity 2 with the insufflator 85, the necessary data is entered into the microprocessor 25 through the touchscreen interface 40, namely, the target pressure value, the maximum safe peak airway pressure value, the incremental pressure value, the predefined dwell time interval, the predefined monitoring time interval, the predefined maximum heart rate value, the predefined minimum heart rate value, the predefined first delay time period and the predefined second delay time period. Additionally, the type of cavity to be insufflated, in this case the peritoneal cavity, the sex, age and body mass index of the subject 3 are also entered into the microprocessor 25 through the touchscreen interface 40 for storing in the memory 42.

During operation of the insufflator 85, the insufflator reads the signal from the second pressure sensor 29 indicative of the cavity pressure, the signal applied to the first receiving port 34 from the pressure sensor 37 of the anaesthesia control and monitoring machine 38 indicative of the peak airway pressure of the subject, and the microprocessor 25 reads the signal applied to the second receiving port 87 from the heart rate monitor 88 indicative of the heart rate of the subject.

The microprocessor 25 reads the signals from the second pressure sensor 25 and the first and second receiving ports 34 and 37substantiantially continuously.

The operation of the insufflator 85 for maintaining the cavity pressure in the peritoneal cavity 2 at the target pressure value is similar to that already described with reference to the insufflator 1 described with reference to Figs. 1 and 2, the microprocessor 25 reads the signal indicative of the cavity pressure from the second pressure sensor 29 and controls the flow controller 19 in response to the cavity pressure read from the second pressure sensor 29 for maintaining the cavity pressure at the target pressure value. The operation of the insufflator 85 for controlling insufflating of the peritoneal cavity 2 in order to maintain the peak airway pressure at or below the maximum safe peak airway pressure is similar to that described with reference to the insufflator 1 of Figs. 1 and 2. The operation of the insufflator 85 for maintaining the rate of insufflating of the peritoneal cavity 2 below the maximum increase in cavity pressure per unit time is similar to that described with reference to the insufflator 75 of Figs. 6 and 7.

In order to control the insufflating of the peritoneal cavity 2 to maintain the heart rate of the subject 3 within the predefined maximum heart rate value and the predefined minimum heart rate value, the microprocessor 25 reads the signal indicative of the heart rate of the subject applied to the second receiving port 87, and compares the read heart rate value of the subject 3 with the predefined maximum heart rate value and with the predefined minimum heart rate value stored in the memory 42. If the read heart rate value of the subject 3 exceeds the predefined maximum heart rate value or falls below the predefined minimum heart rate value, the microprocessor 25 operates the flow controller 19 to isolate the first outlet port 20 from the insufflating gas source 16, commences to time the predefined first delay time period and operates the sounder 43 and the warning light 44 to produce the alert or caution signal. The microprocessor 25 continues to read the signal applied to the second receiving port 87 indicative of the heart rate of the subject 3 during the predefined first delay time period, and on the heart rate of the subject returned to within the predefined maximum heart rate value and the predefined minimum heart rate value, the microprocessor 25 operates the flow controller 19 to reinstate the delivery of insufflating gas to the cavity 2 and maintains the cavity pressure at the cavity pressure at which the heart rate of the subject returned within the predefined maximum heart rate value and the predefined minimum heart rate value.

However, if at the end of the predefined first delay time period, the signal read from the second receiving port 87 indicative of the heart rate of the subject is still indicative of the heart rate of the subject 3 either exceeding the predefined maximum heart rate value or falling below the predefined minimum heart rate value, the microprocessor 25 is programmed to operate the isolating valve 55 from the isolating state to the communicating state to apply vacuum to the peritoneal cavity 2 of the subject 3 to draw insufflating gas from the peritoneal cavity 2 to reduce the cavity pressure to the predefined minimum cavity pressure value. On the cavity pressure being reduced to the minimum cavity pressure value, the microprocessor 25 is programmed to time the predefined second delay time period. At the end of the predefined second delay time period, if the heart rate of the subject 3 has not returned within the predefined maximum heart rate value and the predefined minimum heart rate value, the microprocessor 25 is programmed to operate the sounder 43 and the warning light 44 to produce the warning signal in order to alert the surgeon or the clinician to the fact that the cavity pressure is at the predefined minimum cavity pressure value and the heart rate of the subject either exceeds the predefined maximum heart rate value or is below the predefined minimum heart rate value, so that the surgeon or clinician may take appropriate action to either terminate insufflating of the cavity or to manually control insufflating of the cavity.

Otherwise, the insufflator 85, its operation and use are similar to that of the insufflator 75 described with reference to Figs. 6 and 7.

Referring now to Figs. 11 to 14 there is illustrated an insufflator also according to the invention indicated generally by the reference numeral 100 for insufflating the peritoneal cavity 102 of a human subject 104 during a minimally invasive laparoscopic procedure in the peritoneal cavity 102. The insufflator 100 is configured as will be described below for producing a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject 104. The laparoscopic procedure in the peritoneal cavity 102 is carried out through one or more trocars 105 extending into the peritoneal cavity 102 through the abdominal wall 107 of the subject 104. The peritoneal cavity 102 is insufflated through a gas accommodating conduit 109 from the insufflator 100, connected to one of the trocars 105, for example, the trocar 105a or extending into the peritoneal cavity 102 through the trocar 105a. In this case, the gas accommodating conduit 109 is connected to an insufflating gas port 110 of the trocar 105a.

The insufflator 100 comprises a housing 112, and is suitable for connecting to an external pressurised source of insufflating gas 114, for example, an external pressurised source of carbon dioxide, of the type typically available in a hospital operating theatre, and the insufflator 100 is configured to control the supply and the flow rate of insufflating gas from the insufflating gas source 114 to the peritoneal cavity 102 of the subject 104. A first inlet port 115 located in the housing 112 is provided for connecting the insufflator 100 to the insufflating gas source 114.

A flow controller 117 located in the housing 112 connected between the first inlet port 115 and a first outlet port 119 controls the supply and the delivery rate of insufflating gas from the insufflating gas source 114 to the peritoneal cavity 102. The first outlet port 119 is configured for coupling the gas accommodating conduit 109 thereto so that insufflating gas delivered through the first outlet port 119 is delivered to the peritoneal cavity 102.

A signal processor, in this embodiment of the invention comprising a microprocessor 120 located in the housing 112 controls the insufflator 100 and controls the operation of the flow controller 117 for controlling the supply and the flow rate of insufflating gas through the first outlet port 119 to the peritoneal cavity 102.

A cavity pressure monitoring means for monitoring the pressure in the peritoneal cavity 102 (cavity pressure) comprises a pressure sensor 122 located in the housing 112, and produces a signal indicative of the cavity pressure. The signal produced by the pressure sensor 102 is substantially continuously read by the microprocessor 120 at millisecond intervals, in this case, at 10 millisecond intervals. The microprocessor 120 operates the flow controller 117 for controlling the supply and the flow rate of insufflating gas to the peritoneal cavity 102 in response to the signal indicative of the cavity pressure read from the pressure sensor 122 in order to maintain the cavity pressure at a target pressure value or a set pressure described below. The pressure sensor 122 is connected to a pressure monitoring port 123 in the housing 112. The pressure monitoring port 123 is connected by a connecting conduit 125 to a Veress needle 127 extending through the abdominal wall 107 into the peritoneal cavity 102, so that the cavity pressure is continuously monitored by the pressure sensor 122. However, it will be readily apparent to those skilled in the art that the pressure sensor 122 may be connected through the pressure monitoring port 123 and the connecting conduit 125 to any other suitable connection into the peritoneal cavity 102, for example, it is envisaged that the pressure sensor 122 may be connected by the connecting conduit 125 to an insufflating gas inlet port 129 of the trocar 105b, or the connecting conduit 125 could be entered into the peritoneal cavity 102 through the trocar 105b.

A pressure reducing means for reducing the cavity pressure comprises a venting means in this embodiment of the invention comprising a venting valve 130 located in the housing 112 for venting insufflating gas from the peritoneal cavity 102 to reduce the pressure therein, should it be necessary to reduce the cavity pressure. The venting valve 130 is connected to the first outlet port 119. The venting valve 130 is operated under the control of the microprocessor 120 for venting insufflating gas from the peritoneal cavity 102. However, it is envisaged that in some embodiments of the invention the pressure reducing means for reducing the cavity pressure instead of being provided by a venting valve may be provided by a vacuum applying means for applying a vacuum to the peritoneal cavity 102 for withdrawing insufflating gas therefrom. The vacuum applying means may comprise, for example, a vacuum pump (not shown) located in the housing 112 and operated under the control of the microprocessor 120, or an isolating valve (also not shown) located in the housing 112 and also operated under the control of the microprocessor 120, for selectively connecting the peritoneal cavity 102 with an external vacuum source. Such an external vacuum source typically would be a vacuum source of the type provided in an operating theatre of a hospital. The vacuum pump or the isolating valve would typically be connected to the first outlet port 119, and the isolating valve would typically be connected to the external vacuum source through a second inlet port (not shown) in the housing 112.

An interface comprising a touchscreen interface 132 and a visual display screen 134 are located in a control panel (not shown) of the insufflator 100. The touchscreen interface 132 is operated under the control of the microprocessor 120 and is provided for inputting data into the microprocessor 120 and for displaying data relating to the insufflating of the subject 104. The visual display screen 134 is also operated under the control of the microprocessor 120 and is provided for displaying graphical and other data relating to the insufflating of the subject, as will be described below. The interface instead of comprising a touchscreen and a visual display screen may comprise a touchscreen only or a visual display screen only, and other suitable interface means may be provided for inputting data, for example, a keypad, a voice recognition unit, or any other suitable interface.

An electronic memory 133 of the microprocessor 120, or accessible to the microprocessor 120 is located in the housing 112 for storing data described below in connection with the operation of the insufflator 100.

A means for producing a human sensory perceptible warning signal, in this embodiment of the invention, comprises both a piezoelectric sounder 135 and a warning light 136, both of which are located on the housing 112, and both of which are operated under the control of the microprocessor 120 to produce an audible warning signal and an audible alert signal and a visual warning signal and a visual alert signal, respectively.

In order to provide an understanding of the insufflator 100, the operation of the insufflator 100 will now be described. Initially, the target pressure value at which the peritoneal cavity 102 is to be insufflated is entered into the microprocessor 120 through the touchscreen interface 132, and is stored in the electronic memory 133. Typically, the pressure at which the peritoneal cavity 102 is to be insufflated is between 12mmHg and 15mmHg. An upper pressure differential increase value, and a lower pressure differential increase value, which will be described below, are also entered into the microprocessor 120 through the touchscreen interface 132, and are stored in the memory 133. The insufflator 100 is connected to the insufflating gas source 114 through the first inlet port 115. The gas accommodating conduit 109 is connected to the first outlet port 119 of the insufflator 100 and to the gas inlet port 110 of the trocar 105a. The Veress needle 127 is entered through the abdominal wall 107 into the peritoneal cavity 102 and is connected by the connecting conduit 125 to the pressure monitoring port 123 of the insufflator 100. With the target pressure value and the upper and lower pressure differential increase values entered into the memory 133 of the microprocessor 120, and with the insufflator 100 connected as described, the insufflator 100 is ready for use.

The insufflator 100 is activated and the flow controller 117 is operated under the control of the microprocessor 120 to commence delivery of insufflating gas to the peritoneal cavity 102 of the subject 104. The microprocessor 120 reads the signal from the pressure sensor 122 and operates the flow controller 117 to delivery insufflating gas to the peritoneal cavity 102 for maintaining the pressure in the peritoneal cavity 102 at the target pressure value in response to the signal read by the microprocessor 120 from the pressure sensor 122.

The signal indicative of the pressure produced by the pressure sensor 122 includes an alternating component of the cavity pressure, which is an alternating pressure induced in the cavity pressure by movement of the diaphragm separating the thoracic cavity from the peritoneal cavity 102 of the subject 104 as the diaphragm is urged inwardly and outwardly of the peritoneal cavity 102 by the expansion and contraction of the lungs of the subject 104 as the subject is being ventilated and/or breathing naturally by inhaling and exhaling during each ventilating or breathing cycle.

A waveform 140 representing this alternating component of the cavity pressure is illustrated in Fig. 12 and is displayed on the visual display screen 134. In Fig. 12 cavity pressure is plotted on the Y-axis against time, which is plotted on the X- axis. During ventilating of or breathing by the subject 104, each time air is urged or drawn into the lungs of the subject, the diaphragm is urged into the peritoneal cavity 102, thereby increasing the pressure in the peritoneal cavity, and each time air is drawn or urged out of the lungs of the subject, the diaphragm is urged into the thoracic cavity, thereby reducing the cavity pressure. For so long as the depth of anaesthesia of the subject is relatively deep and in this case at its optimum value, and the subject is being ventilated, the movement of the diaphragm into and out of the peritoneal cavity 102 is low, and thus the pressure differential between adjacent consecutive upper and lower peaks 141 and 142, respectively, of respective consecutive pairs of the peaks 141 and 142 of the waveform 140 of the alternating component of the cavity pressure is relatively small, as illustrated by the portion of the waveform 140 of Fig. 12 from point A at time to to point B at time t₁. In other words, the pressure differential between consecutive adjacent peaks 141 and 142 of the waveform 140 between time to and time t₁ is relatively small. Additionally, the frequency of the alternating component of the cavity pressure during the period from time to to time t₁ while the subject 104 is being ventilated is substantially constant.

However, as the depth of anaesthesia of the subject begins to reduce and the subject 104 commences to breath, the movement of the diaphragm 137 into and out of the peritoneal cavity 102 commences to increase, thereby increasing the pressure differential between adjacent ones of the consecutive upper and lower peaks 141 and 142, respectively, of the waveform 140 of the alternating component of the cavity pressure, as illustrated in the portion of the waveform 140 from point B at time t₁ to point C at time t₂.

The microprocessor 120 is programmed to monitor the alternating component of the cavity pressure from the signal read from the pressure sensor 122 in order to produce a signal indicative of the depth of anaesthesia of the subject. A waveform 143 is illustrated in Fig. 14 representing the depth of anaesthesia of the subject 104. The waveform 143 of Fig. 14 is produced by the microprocessor 120, and is displayed on the visual display screen 134. In Fig. 14 the depth of anaesthesia of the subject 104 is plotted on the Y-axis against time which is plotted on the X-axis.

In order to produce the waveform 143 of Fig. 14, the microprocessor 120 is programmed to determine the pressure differential values between adjacent ones of the consecutive upper and lower peaks 141 and 142, respectively, of the waveform 140 of each cycle of the alternating component of the cavity pressure of Fig. 12. The microprocessor 120 then produces a waveform illustrated in Fig. 13 representing the change in the pressure differential values with respect to time between adjacent ones of the consecutive upper and lower peaks 141 and 142, respectively, of the waveform 140 of Fig. 12 of the respective cycles of the alternating component of the cavity pressure. In Fig. 13 change in the pressure differential values with respect to time is plotted on the Y-axis against time which is plotted on the X-axis.

The pressure differential between the consecutive upper and lower peaks 141 and 142, respectively, of the alternating component of the cavity pressure is inversely proportional to the depth of anaesthesia of a subject. Accordingly, the microprocessor 120 is programmed to invert the waveform 144 of Fig. 13 to produce the waveform 143 of Fig. 14, which is representative of the depth of anaesthesia of the subject.

As can be seen from Fig. 13, an upward step change occurs in the waveform 144 of Fig. 13 at time , which corresponds to an increase in the pressure differential value between the consecutive upper and lower peaks 141 and 142, respectively, which occurs at time t₁ of the waveform 140 of Fig. 12 when the subject 104 commences to breath as the depth of anaesthesia of the subject 104 begins to decrease. A downward step change occurs at time t₁ in the waveform 143 of Fig. 14 representative of the depth of anaesthesia of the subject, which indicates a decrease in the depth of anaesthesia of the subject 104 at time t₁, which corresponds to the upward step change at time t₁ of the waveform 144 of Fig. 13.

The microprocessor 120 is programmed to determine a baseline value of the pressure differential values between the adjacent ones of the consecutive upper and lower peaks 141 and 142, respectively, of the waveform 140 of Fig. 12 which corresponds to the optimum depth of anaesthesia of the subject when the subject is being ventilated. In this case, the baseline value of the pressure differential value is determined by the microprocessor 120 for the portion of the waveform 140 of Fig. 12 from time to to time t₁. Having determined a baseline value of the pressure differential value, the microprocessor 120 compares the current value of the pressure differential value with the baseline value thereof, in order to ascertain if there has been an increase in the current value of the pressure differential above the baseline value thereof. On determining an increase in the pressure differential value above the baseline value thereof, the microprocessor 120 compares the increase in the pressure differential value above the baseline value with the stored upper pressure differential increase value stored in the memory 133. The upper pressure differential increase value which is stored in (he memory 133 is a value of the increase in the pressure differential value above the baseline value thereof which corresponds with a minimum safe permissible reduction in the depth of anaesthesia of the subject from the optimum depth of anaesthesia sufficient to maintain the subject adequately anaesthetised before intervention by an anaesthetist in the anaesthesia of the subject is required.

The microprocessor 120 is programmed to operate the sounder 135 and the warning light 136 to produce a warning signal in response to an increase in the current pressure differential value above the baseline value exceeding the stored upper pressure differential increase value, in order to draw attention to the fact that the depth of anaesthesia of the subject has decreased below the minimum safe permissible depth of anaesthesia sufficient to adequately maintain the subject anesthetised during the procedure.

If the increase in the current pressure differential value above the baseline value thereof does not exceed the stored upper pressure differential increase value, the microprocessor 120 is programmed to compare the increase in the current pressure differential value above the baseline value thereof with the stored lower pressure differential increase value stored in the memory 133. The lower pressure differential increase value is a value which is less than the upper pressure differential increase value, but is sufficiently close to the upper pressure differential increase value, and corresponds with a decrease in the depth of anaesthesia of the subject sufficient to alert to the fact that due to the increase in the current pressure differential value above the baseline value thereof, intervention in the anaesthesia of the subject should be considered since the depth of anaesthesia of the subject is approaching the minimum safe permissible depth of anaesthesia of the subject. The microprocessor 120 is responsive to the increase in the current pressure differential value above the baseline value thereof exceeding the stored lower pressure differential increase value to operate the sounder 135 and the warning light 136 to produce an alert and caution signal alerting to the fact that the depth of anaesthesia of the subject is approaching the minimum safe permissible reduction in the depth of anaesthesia of the subject from the optimum depth of anaesthesia, and preparation should be made for intervention by an anaesthetist in the anaesthesia of the subject.

The microprocessor 120 is programmed to operate the sounder 135 to produce the alert and caution signal as a low frequency series of intermittent bleeps, and to operate the warning light to produce the alert and caution signal by intermittently flashing at a low frequency in response to the increase in the current pressure differential value of the alternating component of the cavity pressure above the baseline value thereof exceeding the stored lower pressure differential increase value. The microprocessor 120 is programmed to operate the sounder 135 to produce the warning signal as a high frequency series of intermittent bleeps and to operate the warning light 136 to produce the warning signal by intermittently flashing at a high frequency, in response to the increase in the current pressure differential value about the baseline value thereof exceeding the stored upper pressure differential increase value. Although, in some embodiments of the invention the microprocessor 120 may be programmed to operate the sounder 135 to produce the warning signal as a continuous series of bleeps and/or to operate the warning light 136 to produce the warning signal by remaining in the continuously on state.

The upper and lower pressure differential increase values may be preset in the memory 133, or may be selectable. In this embodiment of the invention the upper and lower pressure differential increase values are selectable. In general, it is envisaged that the upper predefined pressure differential increase value will be in the order of 1.5mmHg, and the lower pressure differential increase value will be in the order of 1.2mmHg. Although, it is envisaged that the upper and lower pressure differential increase values may be selected to be either higher or lower values than the values of 1 ,2mmHg and 1.5mmHg, respectively, and will largely be dependent on the cavity being insufflated and the age, weight and body mass index of the subject, for example, the upper value of the pressure differential increase value may be as high as 2mmHg or higher, and the lower value of the pressure differential increase value may be as low as 1 mmHg or lower.

In this embodiment of the invention the three waveforms 140, 144 and 143 of Figs. 12 to 14, respectively, are displayed on the visual display screen 134 of the insufflator 100, although in some embodiments of the invention only the waveform 143 indicative of the depth of anaesthesia of the subject may be displayed, although, in general, it is envisaged that at least the waveform 140 of Fig. 12 and the waveform 143 of Fig. 14 would be displayed on the visual display screen 134.

In use, with the insufflator 100 connected to the insufflating gas source 114 and connected to the trocar 105a and to the Veress needle 127 as illustrated in Fig. 11, the insufflator 100 is ready for use. The target pressure value to which the peritoneal cavity 102 of the subject is to be insufflated is entered through the touchscreen interface 132 to the microprocessor 120 and is stored in the memory 133. The lower and upper pressure differential increase values are also entered through the touchscreen interface 132 to the microprocessor 120 and are stored in the memory 133.

The insufflator 100 is then activated to insufflate the peritoneal cavity 102 of the subject 104. The microprocessor 120 operates the flow controller 117 to deliver insufflating gas to the peritoneal cavity 102, and reads signals indicative of the cavity pressure from the pressure sensor 122. The microprocessor 120, in response to the signal read from the pressure sensor 122, controls the operation of the flow controller 117 to maintain the cavity 102 insufflated at the target pressure value. Once the cavity pressure is at the target pressure value and the depth of anaesthesia of the subject is at the optimum depth, the microprocessor 120 monitors the alternating component of the cavity pressure from the signal read from the pressure sensor 122 and determines the baseline value of the pressure differential between the adjacent ones of the consecutive upper and lower peaks 141 and 142, respectively, of the alternating part of the signal read from the pressure sensor 122 indicative of the cavity pressure. The determined value of the baseline pressure differential is stored in the memory 133. The microprocessor 120 then produces the waveforms 140, 144 and 143 of Figs. 12 to 14, which are applied to and displayed on the visual display screen 134, and compares the current pressure differential value with the baseline value thereof.

On detecting an increase in the pressure differential value above the baseline value thereof, the microprocessor 120 compares the detected increase in the pressure differential value above the baseline value thereof, with the upper pressure differential increase values stored in the memory 133. On the detected increase in the pressure differential value exceeding the upper pressure differential increase value stored in the memory 133, the microprocessor 120 operates the sounder 135 and the warning light 136 to produce the warning signal, with the sounder 135 producing the high frequency series of intermittent bleeps and the warning light 136 intermittently flashing at the high frequency. If the detected increase in the pressure differential value above the baseline value thereof does not exceed the upper pressure differential increase value, the microprocessor compares the detected increase in the pressure differential value above the baseline value thereof with the lower pressure differential increase value. If the detected increase in the pressure differential value above the baseline value thereof exceeds the lower pressure differential increase value, the microprocessor 120 operates the sounder 135 and the warning light 136 to produce the alert and caution signal with the sounder 135 producing the low frequency intermittent bleeping signal and the warning light 136 intermittently flashing at the low frequency.

While the change in the pressure differential value above the baseline value thereof with respect to time, as illustrated in the waveform 144 of Fig. 14 has been illustrated as being a step change, it is envisaged that in many cases the change in the increase in the current value of the pressure differential value above the baseline value thereof with respect to time, may not be a simple step change, but may be a gradual change, and in which case, once the change in the increase in the current pressure differential value above the baseline value thereof with respect to time exceeded either the upper or lower pressure differential increase values, the microprocessor 120 would operate the sounder 135 and the warning light 136 appropriately.

As can be seen from the waveform 140 of Fig. 12, the frequency of the alternating component of the cavity pressure is also proportional to the ventilating and natural breathing of the subject, and as the natural breathing of a subject commences to increase as the subject begins to breath as the depth of anaesthesia begins to reduce, the frequency of the alternating component of the cavity pressure also commences to increase. Accordingly, in some embodiments of the invention as well as or instead of monitoring the increase in the pressure differential value above the baseline value thereof in order to determine the depth of anaesthesia, the microprocessor 120 may be programmed to monitor the frequency of the alternating component of the cavity pressure. In which case the microprocessor 120 would be programmed to determine a baseline value for the frequency of the alternating component of the cavity pressure while the anaesthesia of the subject is optimum and the subject is being ventilated. The microprocessor would be programmed to determine the increase in the current value of the frequency of the alternating component of the cavity pressure above the baseline value thereof, and to compare the increase in the current frequency value above the baseline value thereof with stored upper and lower frequency difference values stored in the memory 133, which may be preset in the memory 133 or selectable. The microprocessor 120 would be programmed to operate the sounder 135 and the warning light 136, as already described, if the increase in the current frequency value of the alternating component of the cavity pressure above the baseline value thereof exceeded either the stored upper or lower frequency difference value.

It is envisaged that in some embodiments of the invention only a single pressure differential increase value or a single frequency difference value may be stored in the memory 133 instead of upper and lower values thereof, and in which case, the value of the stored single pressure differential increase value or the stored single frequency difference value would correspond to the upper values thereof, or may correspond with the lower values thereof.

While a particular construction of insufflator 100 has been described, any other suitable construction of insufflator may be used, however, in order to monitor the depth of anaesthesia of the subject, it is important that the cavity pressure is monitored substantially continuously.

It is also envisaged that an apparatus may be provided which would monitor the cavity pressure, and would comprise a signal processor which would be programmed to monitor the alternating component of the cavity pressure in order to determine the depth of anaesthesia of the subject as already described during insufflating of the peritoneal cavity at a target pressure value, a set pressure or a pressure reduced from the target pressure value. Such apparatus may be provided to operate independently of the insufflator, or in conjunction with an insufflator which did not have the facility of monitoring the depth of anaesthesia or the change in depth of anaesthesia of a subject.

While the insufflator 100 described with reference to Figs. 11 to 14 has been described for insufflating the peritoneal cavity of a subject and for monitoring the depth of anaesthesia of the subject, it will be appreciated that the insufflator 100 may also be adapted to monitor the airway pressure of a subject and to control the cavity pressure so that the peak airway pressure of the subject does not exceed the maximum safe peak airway pressure value. In which case, it is envisaged that as the cavity pressure value is reduced below the target pressure value in order to avoid the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value, the microprocessor would be programmed to determine a new baseline pressure differential value or a new baseline frequency differential value each time the target pressure value is reduced and reset.

Additionally, the insufflator 100 may be adapted to also monitor the insufflating rate at which the cavity is being insufflated, and to control the rate of insufflating of the cavity so that the rate of insufflating of the cavity does not exceed the relevant one of stored predefined insufflating rate values as described with reference to the insufflators described with reference to the insufflators described with reference to Figs. 6 to 9. Additionally, the insufflator 100 may also be configured to monitor a characteristic of the heart of the subject, and to control insufflating of the cavity of the subject in order to avoid the characteristic indicative of the performance of the heart of the subject falling below the predefined minimum characteristic value, and in some cases, the insufflator 100 may also be configured to control insufflating of the cavity to avoid the characteristic indicative of the heart of a subject exceeding a predefined maximum value of the characteristic. Needless to say, the apparatus for monitoring the depth of anaesthesia of the subject may be provided for incorporating into each and every one of the insufflators described with reference to Figs. 1 to 10. Needless to say, features of each and every one of the insufflators described with reference to Figs. 1 to 14 and the aspects of the subject being monitored, are interchangeable between the insufflators.

It is also envisaged that the insufflators described with reference to Figs. 1 to 10 may be adapted to monitor the depth of anaesthesia or change in the depth of anaesthesia of a subject in a similar manner to that in which the depth of anaesthesia or the change in the depth of anaesthesia in a subject is determined in the insufflator of Figs. 11 to 14.

While the insufflators have been described for insufflating the peritoneal cavity of a subject, it is envisaged that the insufflators according to the invention may be used for insufflating a cavity, vessel or organ located in the peritoneal cavity, the insufflating of which would have an effect on the peak airway pressure of a subject, or on the heart rate of the subject, or on which the breathing of a subject would have an effect on the pressure in the cavity of a subject being insufflated.

While the signal from the heart rate monitor 88 of the insufflator 85 has been described as being applied to the insufflator through an electrically conductive wire 89 to the second receiving port 87 of the insufflator 85, it is envisaged that in some embodiments of the invention the signal from the heart rate monitor 88 may be transmitted wirelessly from the heart rate monitor 88 for reception by a second receiving means in the form of a second wireless receiver located in the housing 15. In which case, the microprocessor 25 would be configured to read the signal indicative of the heart rate of the subject from the second wireless receiver. Indeed, in some embodiments of the invention a single wireless receiver may be provided to receive both the signal indicative of the airway pressure or the peak airway pressure of the subject and the signal indicative of the heart rate of the subject.

It is also envisaged that in some of the embodiments of the insufflators described with reference to Figs. 6 to 9, instead of providing a look-up table with a large number of age ranges and body mass index ranges, the number of age ranges and the number of body mass index ranges may be reduced. In some embodiments of the invention it is envisaged that the insufflators may be adapted to operate at two maximum insufflating rate values, one of which would be a maximum insufflating rate value for a cavity in an adult subject, and the other of which would be a maximum insufflating rate value for a cavity in a paediatric subject. It is also envisaged that in such cases, the insufflator may be adapted to include a maximum adult insufflating rate value and a maximum paediatric insufflating rate value for insufflating a single cavity only, for example, a peritoneal cavity or for a number of different types of cavities.

It is also envisaged that a default value of a maximum insufflating rate value, for insufflating the peritoneal cavity and/or other cavities may be stored in the memory, and such a default value would be set at a paediatric maximum insufflating rate value.

It is also envisaged that instead of or in addition to including the maximum insufflating rate values in the look-up table based on body mass index ranges, the maximum insufflating rate values may also be based on weight ranges and/or height ranges of different subjects.

While the characteristic indicative of the performance of the heart of the subject has been described in the insufflator described with reference to Fig. 10, as being the heart rate of the subject, it is envisaged that any other suitable characteristic indicative of the performance of the heart besides the heart rate may be monitored, and the signal processor would be responsive to that monitored characteristic indicative of the performance of the heart of the subject in the same way as it has been described as being responsive to the heart rate of the subject. For example, it is envisaged that the characteristic indicative of the performance of the heart of the subject may be the blood pressure of the subject, and in which case the microprocessor 25 of the insufflator 85 of Fig. 10 would be configured to read the signal indicative of the blood pressure of the subject at the predefined time intervals or substantially continuously, and each time the signal indicative of the blood pressure of the subject is read, the microprocessor would compare the read signal indicative of the blood pressure of the subject with one or more stored predefined maximum and/or minimum systolic blood pressure values and/or predefined maximum and/or minimum diastolic blood pressure values. If the read systolic or diastolic blood pressure values exceeded the stored predefined maximum systolic or diastolic blood pressure values or fell below the predefined minimum systolic or diastolic blood pressure values, the microprocessor would operate the flow controller to terminate insufflating of the cavity, and if the blood pressure of the subject failed to return within the predefined maximum systolic and/or diastolic blood pressure values and the predefined minimum systolic and/or diastolic blood pressure values within the respective predefined first and second delay time periods, the microprocessor would operate the insufflator to pause insufflating of the cavity and/or withdraw insufflating gas from the peritoneal cavity in a similar manner as already described with reference to Fig. 10.

It is also envisaged that the insufflators described with reference to Figs.6 to 9, may also be adapted to receive a signal indicative of a characteristic indicative of the performance of the heart of a subject, and in which case, the signal processor thereof would also be responsive to the signal indicative of the characteristic of the performance of the heart of the subject for controlling the operation of the flow controllers of the insufflators as described with reference to the insufflator of Fig. 10.

While the flow sensor 82 of the insufflator 80 of Figs. 8 and 9 has been described as producing a signal indicative of the flow rate of insufflating gas being delivered to the cavity 2, in some embodiments of the invention the flow sensor may be of the type which also produces a signal indicative of the flow of insufflating gas to the cavity. In which case, each time the microprocessor reads the signal from the flow sensor 82, the microprocessor would compute the flow rate of the insufflating gas being delivered to the cavity 2, and would then compare the computed flow rate of insufflating gas to the cavity 2 with the stored selected appropriate one of the stored predefined maximum flow rate values from the look-up table 81.

It will also be appreciated that while the signal processor of the insufflators has been described as comprising a microprocessor, any suitable signal processor, for example, a microcontroller or any other such signal processor may be used. It will of course be appreciated that any suitable interface besides a touchscreen may be provided for inputting data to the microprocessor.

While the insufflators have been described for insufflating a peritoneal cavity in a human subject, the insufflators may be used for insufflating the cavity in any organ within the peritoneal or any cavity in the body of a human or animal subject.

Additionally, it will be appreciated that while the look-up tables described with reference to Figs. 7 and 9 have been provided for the cavities of male subjects of specific age ranges and body mass index ranges, a corresponding look-up table for the peritoneal cavity of female subjects of similar age ranges and body mass index ranges will be stored in the memory. Furthermore, it will be appreciated that in some embodiments of the invention more or less age ranges may be provided in each look-up table than described, and more or less body mass index ranges may be provided in the look-up table than described.

While the insufflating gas has been described as carbon dioxide, any other suitable insufflating gas may be used.

Needless to say, while the insufflating gas has been described as being delivered to the peritoneal cavity through an insufflating gas port of a trocar, in cases where a trocar is provided without an insufflating gas port, the gas accommodating conduit 10 may be entered into the cavity through any other means, for example, directly through the instrument bore of a trocar or a Veress needle.

It will also be appreciated that the cavity pressure may be monitored through any other suitable communicating means, and in some cases may be monitored through a conduit extending into the cavity through an instrument channel of a trocar. It is also envisaged that in some embodiments of the invention the pressure sensor may be located in the cavity, for example, on the outer surface of a trocar adjacent a distal end of the trocar which would be located within the cavity, and in which case, a signal indicative of the pressure in the cavity would be transmitted to the microprocessor, either wirelessly or through hardwiring from the pressure sensor. It is also envisaged that the cavity pressure may be monitored through the conduit 10 of the insufflators described with reference to Figs. 1 to 10, and in which case, insufflating of the cavity would have to be paused each time a cavity pressure reading is being taken by the first pressure sensor 27, or alternatively, instead of pausing insufflating of the cavity, the microprocessor would be programmed to determine the pressure in the cavity by using a compensating factor to compensate for the reduction in pressure along the length of the conduit 10 due to flow resistance therein.

While in the embodiments of the invention described with reference to Figs. 1 to 10, the airway pressure has been derived from a pressure sensor located in an anaesthesia control and monitoring machine or a ventilator, it is envisaged that the airway pressure or the peak airway pressure may be derived from any suitable source from which the airway pressure is available. In some embodiments of the invention it is envisaged that a dedicated pressure sensor may be provided for determining the airway pressure of the subject.

While in the embodiments of the insufflators described with reference to Figs. 1 to 14, various means for reducing the pressure in the peritoneal cavity of the subject have been described, it is envisaged that the means for reducing the pressure in the peritoneal cavity are interchangeable between the respective embodiments of the insufflators described with reference to Figs. 1 to 14.

It will also be appreciated that while in the insufflator described with reference to Fig. 5 the signal indicative of the peak airway pressure of the subject has been described as being transmitted wirelessly from the anaesthesia control and monitoring machine to the insufflator by a Bluetooth protocol, the signal indicative of the airway pressure or the peak airway pressure may be transmitted from the anaesthesia control and monitoring machine or from any other source from which the airway pressure is derived by any other suitable wireless protocol.

It will also be appreciated that while the insufflators of Figs. 1 to 14 have been described for use in insufflating the peritoneal cavity, it will be appreciated that the insufflators described with reference to Figs. 1 to 14 may be used for insufflating any cavity in the peritoneal cavity, or indeed any other cavity in the body of a subject, the insufflating of which would increase pressure applied to the lungs of a subject, and thereby would increase the peak airway pressure, would induce an alternating pressure component on the cavity pressure, or would have an effect on the heart of a subject, be the subject a human subject or an animal subject.

Needless to say, it will be appreciated that the insufflators described with reference to Figs. 6 to 9 may also be used for insufflating any cavity in the body of a human or animal subject besides the peritoneal cavity. While the insufflators of the different embodiments of the invention have been described for insufflating a cavity in the body of a human subject, it will be readily apparent to those skilled in the art that the insufflators may also be used for insufflating any cavity in the body of an animal subject.

While in the insufflator described with reference to Fig. 10 has been described as comprising a microprocessor configured to operate the insufflator to control delivery of insufflating gas to the cavity of the subject,

(a) to avoid the peak airway pressure of the subject exceeding a maximum safe peak airway pressure value,

(b) to avoid the rate of insufflating of the cavity exceeding an insufflating rate appropriate to the sex, age and body mass index of the subject, and

(c) to avoid a characteristic indicative of the performance of the heart of the subject exceeding a predefined maximum upper value of the characteristic, or falling below a predefined minimum lower value of the characteristic, it is envisaged that the signal processor of the insufflator may be configured to operate the insufflator to control delivery of insufflating gas to the cavity of a subject solely for the purpose of avoiding the peak airway pressure of a subject exceeding a maximum safe peak airway pressure value, or solely for the purpose of avoiding a characteristic indicative of the performance of the heart of a subject exceeding a predefined maximum upper value of the characteristic, or falling below a predefined minimum lower value of the characteristic. It is also envisaged that the microprocessor of the insufflator described with reference to Fig. 10 may be configured to operate the insufflator to control delivery of insufflating gas to the cavity of a subject in order to avoid the peak airway pressure of a subject exceeding a maximum safe peak airway pressure value, and also to avoid a characteristic indicative of the performance of the heart of a subject exceeding a predefined maximum upper value of the characteristic or falling below a predefined minimum lower value of the characteristic. In each of these embodiments of the invention the microprocessor of the insufflator of Fig. 10 would not operate the flow controller to control delivery of insufflating gas to the cavity of a subject in order to avoid the rate of insufflating of the cavity of the subject exceeding an insufflating rate appropriate to the sex, age or age range, or body mass index or body mass index range of the subject.

While the insufflators and the method for insufflating a cavity in the body of a human or animal subject have been described for use in a laparoscopic minimally invasive procedure, it is envisaged that the insufflators and/or the methods for insufflating a cavity in the body of a human or animal subject during a minimally invasive procedure may be used during insufflating of a cavity in the body of a human or animal subject during a minimally invasive procedure being carried out by an endoscope, or being carried out laparoscopically and in conjunction with an endoscope.

Claims

1. An insufflator for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the insufflator comprising: a flow controller adapted for controlling the delivery of insufflating gas to the cavity, a first receiving means adapted for receiving a signal indicative of airway pressure in the airway of the subject, an electronic memory adapted to store a maximum safe airway pressure value, and a signal processor programmed to read the value of the signal indicative of the airway pressure of the subject from the first receiving means, to compare the read value of the signal indicative of the airway pressure of the subject with the stored maximum safe airway pressure value, and to operate the flow controller to reduce the pressure in the cavity (cavity pressure) in response to the read value of the signal indicative of the airway pressure of the subject exceeding the maximum safe airway pressure value.

2. An insufflator as claimed in Claim 1 in which the maximum safe airway pressure value is stored as a maximum safe peak airway pressure value.

3. An insufflator as claimed in Claim 2 in which the airway pressure of the subject which is compared with the maximum safe peak airway pressure value is the peak airway pressure value of the subject, and the signal processor is programmed to operate the flow controller to reduce the cavity pressure in response to the peak airway pressure value of the subject exceeding the stored maximum safe peak airway pressure value.

4. An insufflator as claimed in any preceding claim in which the signal processor is programmed to operate the flow controller to reduce the cavity pressure by reducing the rate of delivery of insufflating gas to the cavity.

5. An insufflator as claimed in any preceding claim in which the signal processor is programmed to operate the flow controller to reduce the cavity pressure by temporarily terminating delivery of insufflating gas to the cavity.

6. An insufflator as claimed in any preceding claim in which the insufflator comprises a pressure reducing means configured to reduce the cavity pressure, the signal processor being programmed to operate the pressure reducing means for reducing the cavity pressure in response to the read value of the signal indicative of the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

7. An insufflator as claimed in Claim 6 in which the pressure reducing means comprises a venting means for venting the cavity.

8. An insufflator as claimed in Claim 7 in which the venting means comprises a venting valve.

9. An insufflator as claimed in any of Claims 6 to 8 in which the pressure reducing means comprises a vacuum applying means for applying a vacuum to the cavity.

10. An insufflator as claimed in Claim 9 in which the vacuum applying means comprises a vacuum pump, or a communicating means for selectively communicating the cavity with a vacuum source, and preferably, the communicating means comprises an isolating valve alternately operable in a communicating state communicating the cavity with the vacuum source, and in an isolating state isolating the cavity from the vacuum source.

11. An insufflator as claimed in any preceding claim in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to reduce the cavity pressure in incremental pressure reducing steps in response to the read value of the signal indicative of the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

12. An insufflator as claimed in Claim 11 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means for maintaining the cavity pressure substantially constant at the current reduced cavity pressure value for a predefined dwell time interval each time the cavity pressure is reduced by one of the incremental pressure reducing steps.

13. An insufflator as claimed in Claim 11 or 12 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is the same as the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

14. An insufflator as claimed in Claim 11 or 12 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is greater than or less than the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

15. An insufflator as claimed in Claim 14 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step plus the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps.

16. An insufflator as claimed in Claim 14 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value in the range of 1.5 times to 3 times the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

17. An insufflator as claimed in Claim 16 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value of approximately twice the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

18. An insufflator as claimed in any of Claims 12 to 17 in which each predefined dwell time interval lies in the range of 0.5 minutes to 2 minutes.

19. An insufflator as claimed in any of Claims 12 to 18 in which each predefined dwell time interval lies in the range of 0.75 minutes to 1.5 minutes.

20. An insufflator as claimed in any of Claims 12 to 19 in which each predefined dwell time interval is approximately 1 minute.

21. An insufflator as claimed in any of Claims 11 to 20 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps lies in the range of 0.5mmHg to 2mmHg.

22. An insufflator as claimed in any of Claims 11 to 21 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps is approximately 1mmHg.

23. An insufflator as claimed in any preceding claim in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to reduce the cavity pressure until the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

24. An insufflator as claimed in Claim 23 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to cease reducing the cavity pressure in response to the cavity pressure being reduced to a predefined minimum cavity pressure value before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

25. An insufflator as claimed in Claim 24 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to maintain the cavity pressure at a reduced cavity pressure value corresponding to the cavity pressure value at which the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or at the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to the maximum safe peak airway pressure value.

26. An insufflator as claimed in Claim 24 or 25 in which the signal processor is programmed to produce a warning signal convertible to a human sensory perceptible signal in response to the cavity pressure being reduced to the predefined minimum cavity pressure value.

27. An insufflator as claimed in any of Claims 24 to 26 in which the predefined minimum cavity pressure value comprises a cavity pressure value consistent with producing a minimum working volume in the cavity.

28. An insufflator as claimed in any of Claims 23 to 27 in which the predefined minimum cavity pressure value lies in the range of 3mmHg to 8mmHg.

29. An insufflator as claimed in any of Claims 23 to 28 in which the predefined minimum cavity pressure value is approximately 5mmHg.

30. An insufflator as claimed in any preceding claim in which the first receiving means is adapted for receiving the signal indicative of the airway pressure or the peak airway pressure of the subject electronically.

31. An insufflator as claimed in any preceding claim in which the first receiving means comprises a receiving port configured for coupling to a wire electronically carrying the signal indicative of the airway pressure or the peak airway pressure of the subject.

32. An insufflator as claimed in any of Claims 1 to 29 in which the first receiving means comprises a first wireless receiver for receiving the signal indicative of the airway pressure or the peak airway pressure of the subject.

33. An insufflator as claimed in any preceding claim in which the signal indicative of the airway pressure or the peak airway pressure of the subject is derived from an airway pressure monitoring means adapted to monitor the airway pressure of the subject.

34. An insufflator as claimed in Claim 33 in which the airway pressure monitoring means comprises an airway pressure monitoring sensor of an anaesthesia control and monitoring machine controlling and monitoring the depth of anaesthesia of the subject.

35. An insufflator as claimed in Claim 33 or 34 in which the airway pressure monitoring means comprises an airway pressure monitoring sensor located in a ventilator ventilating the subject.

36. An insufflator as claimed in any preceding claim in which the insufflator comprises the airway pressure monitoring means, and the airway pressure monitoring means is adapted for coupling to an endotracheal tube through which the subject is being ventilated.

37. An insufflator as claimed in any preceding claim in which the airway pressure monitoring means is adapted to produce a signal indicative of the peak airway pressure value of the subject.

38. An insufflator as claimed in any of Claims 1 to 36 in which the airway pressure monitoring means is adapted to produce a signal indicative of the airway pressure of the subject, and the signal processor is programmed to determine the peak airway pressure of the subject from the signal produced by the airway pressure monitoring means indicative of the airway pressure of the subject.

39. An insufflator as claimed in any preceding claim in which a cavity pressure monitoring means is provided, the cavity pressure monitoring means being adapted to monitor the cavity pressure and to produce a signal indicative of the cavity pressure, and the signal processor is programmed to read the signal indicative of the cavity pressure produced by the cavity pressure monitoring means.

40. An insufflator as claimed in Claim 39 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means in response to the signal indicative of the cavity pressure read from the cavity pressure monitoring means for maintaining the cavity pressure at a target pressure value until the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value.

41. An insufflator as claimed in Claim 39 or 40 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means in response to the signal indicative of the cavity pressure read from the cavity pressure monitoring means for maintaining the cavity pressure at a pressure not exceeding a value equal to the maximum safe peak airway pressure value, or at a pressure below or just below the value of the maximum safe peak airway pressure value.

42. An insufflator as claimed in any preceding claim in which the insufflator comprises an insufflating monitoring means for monitoring insufflating of the cavity and for producing a signal indicative of the insufflating of the cavity, and the signal processor is programmed to read the signal produced by the insufflating monitoring means indicative of the insufflating of the cavity, to determine the rate at which the cavity is being insufflated from the signal read from the insufflating monitoring means, to compare the determined rate at which the cavity is being insufflated with a stored maximum insufflating rate value stored in the electronic memory, and to operate the flow controller to prevent the rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

43. An insufflator as claimed in Claim 42 in which the signal processor is programmed to operate the flow controller to reduce the flow rate at which insufflating gas is being delivered to the cavity or to temporarily pause delivery of insufflating gas to the cavity in response to the determined rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

44. An insufflator as claimed in Claim 42 or 43 in which the stored maximum insufflating rate value is stored as a function of cavity pressure.

45. An insufflator as claimed in Claim 44 in which the signal processor is programmed to determine the rate at which the cavity is being insufflated as a function of the cavity pressure.

46. An insufflator as claimed in any of Claims 42 to 45 in which the stored maximum insufflating rate value is stored as a value of a maximum increase in cavity pressure per unit time.

47. An insufflator as claimed in Claim 46 in which the signal processor is programmed to determine the rate at which the cavity is being insufflated as the increase in the cavity pressure per unit time.

48. An insufflator as claimed in any preceding claim in which the insufflating monitoring means for monitoring insufflating of the cavity comprises the cavity pressure monitoring means configured to monitor the cavity pressure.

49. An insufflator as claimed in any of Claims 42 to 48 in which the stored maximum insufflating rate value is stored as a function of the flow of the insufflating gas delivered to the cavity.

50. An insufflator as claimed in Claim 49 in which the signal processor is programmed to determine the rate at which the cavity is being insufflated as a function of the flow of the insufflating gas being delivered to the cavity.

51. An insufflator as claimed in Claim 49 or 50 in which the stored maximum insufflating rate value is stored as a value of a maximum rate of delivery of insufflating gas to the cavity.

52. An insufflator as claimed in Claim 51 in which the signal processor is programmed to determine the rate at which the cavity is being insufflated as the flow rate at which the insufflating gas is being delivered to the cavity.

53. An insufflator as claimed in any preceding claim in which the insufflating monitoring means comprises a flow sensor for monitoring the flow of insufflating gas to the cavity and for producing a signal indicative of the flow of insufflating gas to the cavity.

54. An insufflator as claimed in any of Claims 42 to 53 in which a plurality of maximum insufflating rate values are stored in the electronic memory for respective subjects of different types.

55. An insufflator as claimed in any of Claims 42 to 54 in which a plurality of maximum insufflating rate values are stored for subjects of one or more respective different ages or different age ranges, of respective different weights or different weight ranges, or of respective different body mass indices or different body mass index ranges.

56. An insufflator as claimed in any of Claims 40 to 55 in which a plurality of maximum insufflating rate values are stored for subjects of different sexes.

57. An insufflator as claimed in any of Claims 40 to 56 in which a plurality of maximum insufflating rate values are stored for different cavities of the respective different subjects.

58. An insufflator as claimed in any of Claims 40 to 57 in which a plurality of maximum insufflating rate values are stored for the peritoneal cavity of the respective different types of subjects.

59. An insufflator as claimed in any preceding claim in which a predefined minimum value of a characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall is stored in the electronic memory, and the signal processor is programmed to read a value of a signal indicative of a characteristic of the performance of the heart of the subject, to compare the read value of the signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined minimum value of the characteristic, and to operate the flow controller to reduce the rate of delivery of insufflating gas to the cavity or to cease delivery of insufflating gas to the cavity, or to operate the pressure reducing means to reduce the cavity pressure in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the stored predefined minimum value of the characteristic.

60. An insufflator as claimed in Claim 59 in which the signal processor is programmed to operate the pressure reducing means to vent or withdraw insufflating gas from the cavity in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the stored predefined minimum value of the characteristic.

61. An insufflator as claimed in Claim 59 or 60 in which the predefined minimum value of the characteristic indicative of the performance of the heart of the subject stored in the electronic memory comprises a predefined minimum value of the heart rate of a subject, below which the heart rate of a subject should not fall, and the signal processor is programmed to read a signal indicative of the characteristic of the performance of the heart of the subject as the heart rate of the subject.

62. An insufflator as claimed in any preceding claim in which a predefined maximum value of a characteristic indicative of a maximum performance value, above which the performance of a heart of a subject should not exceed is stored in the electronic memory, and the signal processor is programmed to read a value of a signal indicative of a characteristic of the performance of the heart of the subject, to compare the read value of the signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined maximum value of the characteristic, and to operate the flow controller to reduce the rate of delivery of insufflating gas to the cavity or to cease delivery of insufflating gas to the cavity, or to operate the pressure reducing means to reduce the cavity pressure in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject exceeding the stored predefined maximum value of the characteristic.

63. An insufflator as claimed in Claim 62 in which the signal processor is programmed to operate the pressure reducing means to vent or withdraw insufflating gas from the cavity in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject exceeding the stored predefined maximum value of the characteristic.

64. An insufflator as claimed in Claim 62 or 63 in which the predefined maximum value of the characteristic indicative of the performance of the heart of the subject stored in the electronic memory comprises a predefined maximum value of the heart rate of a subject, above which the heart rate of a subject should not exceed, and the signal processor is programmed to read a signal indicative of the characteristic of the performance of the heart of the subject as the heart rate of the subject.

65. An insufflator as claimed in any of Claims 59 to 64 in which the insufflator comprises a second receiving means adapted for receiving the signal indicative of the characteristic of the performance of the heart of the subject, and the signal processor is programmed to read the signal indicative of the characteristic of the performance of the heart of the subject from the second receiving means.

66. An insufflator as claimed in Claim 65 in which the second receiving means comprises a second receiving port configured for coupling to a wire electronically carrying the signal indicative of the characteristic of the performance of the heart of the subject, or a second wireless receiver for wirelessly receiving the signal indicative of the characteristic of the performance of the heart of the subject.

67. An insufflator as claimed in any of Claims 59 to 66 in which a heart performance monitoring means is provided for monitoring the characteristic indictive of the performance of the heart of a subject and to produce a signal indicative of the characteristic of the performance of the heart of the subject from the heart performance monitoring means.

68. An insufflator as claimed in Claim 67 in which the heart performance monitoring means for monitoring the characteristic indicative of the performance of the heart of a subject is adapted for monitoring the heart rate of the subject.

69. An insufflator as claimed in any preceding claim in which an interface is provided, and the signal processor is programmed to read signals and data inputted through the interface and to store the inputted data in the electronic memory.

70. An insufflator as claimed in Claim 69 in which the interface is adapted for inputting of the target pressure value at which the cavity is to be insufflated.

71. An insufflator as claimed in Claim 69 or 70 in which the interface is adapted for inputting the maximum safe peak airway pressure value.

72. An insufflator as claimed in any of Claims 69 to 71 in which the interface is adapted for inputting the predefined minimum value of the characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall, and/or the predefined maximum value of a characteristic indicative of the maximum performance value above which the performance of a heart of a subject should not exceed.

73. An insufflator as claimed in any of Claims 69 to 72 in which the interface is adapted for inputting at least one or more of the sex, the age or the age range, weight or weight range, or the body mass index or the body mass index range of the subject, and the signal processor is programmed to select the appropriate maximum insufflating rate value from the stored values thereof in response to data indicative of at least one of the sex, the age or the age range, the weight or the weight range, or the body mass index or the body mass index range of the subject entered through the interface.

74. An insufflator as claimed in any preceding claim in which the signal processor is programmed to store a default value of the maximum insufflating rate of a subject, and preferably, the default value of the maximum insufflating rate of a subject comprises the maximum insufflating rate stored for a subject of at least one of a subject of female sex, of the youngest age or age range, the lowest weight or weight range and/or the lowest body mass index or body mass index range.

75. An insufflator as claimed in any preceding claim in which the signal processor is programmed to monitor a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure read from the cavity pressure monitoring means, to determine the depth of anaesthesia or change in the depth of anaesthesia of the subject from the monitored characteristic indicative of the depth of anaesthesia, and to produce a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject.

76. An insufflator as claimed in Claim 75 in which the characteristic indicative of the depth of anaesthesia of the subject monitored by the signal processor from the signal indicative of the cavity pressure read from the cavity pressure monitoring means comprises an alternating component of the signal indicative of the cavity pressure.

77. An insufflator as claimed in Claim 76 in which the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

78. An insufflator as claimed in Claim 77 in which the signal processor is programmed to determine the depth of anaesthesia or the change in the depth of anaesthesia of the subject as a function of the pressure differential between consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure.

79. An insufflator for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the insufflator comprising: a flow controller adapted for controlling the delivery of insufflating gas to the cavity, one or both of a first receiving means adapted for receiving a signal indicative of airway pressure in the airway of the subject, and/or a second receiving means adapted for receiving a signal indicative of a characteristic of the performance of the heart of the subject, an electronic memory adapted to store one or both of a maximum safe airway pressure value, and/or a predefined minimum value of a characteristic indicative of the performance of the heart of a subject, and a signal processor programmed to read the signal indicative of the airway pressure of the subject from the first receiving means, and/or to read the signal indicative of the characteristic of the performance of the heart of the subject, to compare the read signal indicative of the airway pressure of the subject with the stored maximum safe airway pressure value, and/or to compare the read signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined minimum value of the characteristic indicative of the performance of the heart of a subject, and to operate the flow controller to one of reduce the rate of delivery of insufflating gas to the cavity of the subject, or to cease delivery of insufflating gas to the cavity of the subject for reducing the cavity pressure, in response to the read value indicative of the airway pressure of the subject exceeds the maximum safe airway pressure value, or in response to the read value indicative of the characteristic of the performance of the heart of the subject falling below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject.

80. An insufflator as claimed in Claim 79 in which the maximum safe airway pressure value is stored as a maximum safe peak airway pressure value, and the airway pressure of the subject which is compared with the maximum safe airway pressure value is the peak airway pressure value of the subject, and the signal processor is programmed to operate the flow controller to reduce the cavity pressure in response to the peak airway pressure value of the subject exceeding the stored maximum safe peak airway pressure value.

81. An insufflator as claimed in Claim 79 or 80 in which a predefined maximum value of a characteristic indicative of the performance of the heart of a subject is stored in the electronic memory, and the signal processor is programmed to compare the read signal indicative of the characteristic of the performance of the heart of the subject with the stored predefined maximum value of the characteristic indicative of the performance of the heart of a subject.

82. An insufflator as claimed in any of Claims 79 to 81 in which the signal processor is programmed to operate the flow controller to one of reduce the rate of delivery of insufflating gas to the cavity of the subject or to cease delivery of insufflating gas to the cavity of the subject for reducing the cavity pressure, in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject exceeding the predefined maximum value of the characteristic stored in memory.

83. An insufflator as claimed in any of Claims 79 to 82 in which a pressure reducing means is provided for reducing the cavity pressure, and the signal processor is programmed to operate the pressure reducing means to reduce the cavity pressure in response to the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value, or the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the predefined minimum value of the characteristic indicative of the performance of the heart of a subject, or exceeding the predefined maximum value of the characteristic indicative of the performance of the heart of a subject.

84. An insufflator as claimed in Claim 83 in which the pressure reducing means comprises a venting means.

85. An insufflator as claimed in Claim 83 or 84 in which the pressure reducing means comprises a means for applying a vacuum to the cavity of the subject.

86. An insufflator as claimed in any of Claims 83 to 85 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to reduce the cavity pressure in incremental pressure reducing steps.

87. An insufflator as claimed in Claim 86 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means for maintaining the cavity pressure substantially constant at the current cavity pressure for a predefined dwell time interval at the end of each incremental pressure reducing step.

88. An insufflator as claimed in Claim 86 or 87 in which the signal processor is programmed to reduce the cavity pressure by an incremental pressure value in each incremental pressure reducing step.

89. An insufflator as claimed in Claim 88 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is the same as the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

90. An insufflator as claimed in Claim 88 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is greater than or less than the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

91. An insufflator as claimed in Claim 90 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step plus the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps.

92. An insufflator as claimed in Claim 90 or 91 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value in the range of 1.5 times to 3 times the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

93. An insufflator as claimed in any of Claims 90 to 92 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value of approximately twice the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

94. An insufflator as claimed in any of Claims 87 to 93 in which each predefined dwell time interval lies in the range of 0.5 minutes to 2 minutes.

95. An insufflator as claimed in any of Claims 87 to 94 in which each predefined dwell time interval lies in the range of 0.75 minutes to 1.5 minutes.

96. An insufflator as claimed in any of Claims 87 to 95 in which each predefined dwell time interval is approximately 1 minute.

97. An insufflator as claimed in any of Claims 88 to 96 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps lies in the range of 0.5mmHg to 2mmHg.

98. An insufflator as claimed in any of Claims 88 to 97 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps is approximately 1 mmHg.

99. An insufflator as claimed in any of Claims 86 to 98 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means for maintaining the cavity pressure substantially constant at the current reduced cavity pressure value for a predefined dwell time interval each time the cavity pressure is reduced by one of the incremental pressure reducing steps.

100. An insufflator as claimed in any of Claims 83 to 99 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to reduce the cavity pressure until the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

101. An insufflator as claimed in Claim 100 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to cease reducing the cavity pressure in response to the cavity pressure being reduced to a predefined minimum cavity pressure value before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

102. An insufflator as claimed in Claim 101 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means to maintain the cavity pressure at a reduced cavity pressure corresponding to the cavity pressure value at which the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or the read value of the signal indicative of the characteristic of the performance of the heart of the subject being within the predefined minimum value of the characteristic indicative of the performance of the heart of the subject, and the predefined maximum value of the characteristic indicative of the performance of the heart of the subject, whichever is the lowest cavity pressure, or at the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or the characteristic indicative of the performance of the heart of the subject is within the predefined minimum and maximum values of the characteristic thereof.

103. An insufflator as claimed in Claim 101 or 102 in which the signal processor is programmed to produce a warning signal convertible to a human sensory perceptible signal warning that the cavity pressure has been reduced to the predefined minimum cavity pressure value.

104. An insufflator as claimed in any of Claims 101 to 103 in which the predefined minimum cavity pressure value comprises a cavity pressure value consistent with producing a minimum working volume in the cavity.

105. An insufflator as claimed in any of Claims 101 to 104 in which the predefined minimum cavity pressure value lies in the range of 3mmHg to 8mmHg.

106. An insufflator as claimed in any of Claims 101 to 105 in which the predefined minimum cavity pressure value is approximately 5mmHg.

107. An insufflator as claimed in any of Claims 83 to 106 in which the signal processor is programmed to operate the flow controller and/or the pressure reducing means in response to the signal read from the cavity pressure monitoring means for maintaining the cavity pressure at a target pressure value, until the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value, the signal indicative of the characteristic of the performance of the heart of the subject is below the predefined minimum value of the characteristic indicative of the performance of the heart of the subject or is above the predefined maximum value of the characteristic indicative of the performance of the heart of the subject.

108. An insufflator as claimed in any of Claims 79 to 107 in which the insufflator comprises an insufflating monitoring means for monitoring insufflating of the cavity and for producing a signal indicative of the insufflating of the cavity, the signal processor being programmed to read the signal produced by the insufflating monitoring means indicative of the insufflating of the cavity, to determine the rate at which the cavity is being insufflated from the signal read from the insufflating monitoring means, to compare the determined rate at which the cavity is being insufflated with a stored maximum insufflating rate value stored in the electronic memory, and to operate the flow controller to prevent the rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

109. An insufflator as claimed in Claim 108 in which the signal processor is programmed to operate the flow controller to reduce the flow rate at which insufflating gas is being delivered to the cavity or to temporarily pause delivery of insufflating gas to the cavity in response to the determined rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

110. An insufflator as claimed in Claim 108 or 109 in which the stored maximum insufflating rate value is stored as a function of cavity pressure.

111. An insufflator as claimed in Claim 110 in which the signal processor is programmed to determine the rate of insufflating of the cavity as a function of the cavity pressure.

112. An insufflator as claimed in any of Claims 108 to 111 in which the stored maximum insufflating rate value is stored as a value of a maximum increase in cavity pressure per unit time.

113. An insufflator as claimed in Claim 112 in which the signal processor is programmed to determine the rate at which the cavity is being insufflated as the increase in the cavity pressure per unit time.

114. An insufflator as claimed in any of Claims 110 to 113 in which the insufflating monitoring means for monitoring insufflating of the cavity comprises the cavity pressure monitoring means adapted to monitor the cavity pressure, and to produce a signal indicative of the cavity pressure.

115. An insufflator as claimed in any of Claims 108 to 114 in which the stored maximum insufflating rate value is stored as a function of the flow of the insufflating gas delivered to the cavity.

116. An insufflator as claimed in Claim 115 in which the signal processor is programmed to determine the rate at which the cavity is being insufflated as a function of the flow at which the insufflating gas is being delivered to the cavity.

117. An insufflator as claimed in any of Claims 108 to 116 in which the stored maximum insufflating rate value is stored as a value of a maximum rate of delivery of insufflating gas to the cavity.

118. An insufflator as claimed in Claim 117 in which the signal processor is programmed to determine the rate at which the cavity is being insufflated as the flow rate at which the insufflating gas is being delivered to the cavity.

119. An insufflator as claimed in any of Claims 115 to 118 in which the insufflating monitoring means comprises a flow sensor for monitoring the flow of insufflating gas to the cavity and for producing a signal indicative of the flow of insufflating gas to the cavity.

120. An insufflator as claimed in any of Claims 108 to 119 in which a plurality of maximum insufflating rate values are stored in the electronic memory for a plurality of respective subjects of different types.

121. An insufflator as claimed in any of Claims 108 to 120 in which a plurality of maximum insufflating rate values are stored for subjects of different ages or different age ranges.

122. An insufflator as claimed in any of Claims 108 to 121 in which a plurality of maximum insufflating rate values are stored for subjects of different weights or different weight ranges.

123. An insufflator as claimed in any of Claims 108 to 122 in which a plurality of maximum insufflating rate values are stored for subjects of different body mass indices or different body mass index ranges.

124. An insufflator as claimed in any of Claims 108 to 123 in which a plurality of maximum insufflating rate values are stored for subjects of respective different sexes.

125. An insufflator as claimed in any of Claims 108 to 124 in which a plurality of maximum insufflating rate values are stored for different cavities of the respective different subjects.

126. An insufflator as claimed in any of Claims 108 to 125 in which a plurality of maximum insufflating rate values are stored for the peritoneal cavity of the respective different types of subjects.

127. An insufflator for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the insufflator comprising a flow controller for controlling delivery of insufflating gas to the cavity, a cavity pressure monitoring means for monitoring pressure in the cavity and producing a signal indicative of the cavity pressure, and a signal processor programmed to read the signal indicative of the cavity pressure produced by the cavity pressure monitoring means, and to operate the flow controller to deliver insufflating gas to the cavity and to maintain the cavity pressure at a target pressure value or a pressure value below the target pressure value in response to the signal indictive of the cavity pressure read from the cavity pressure monitoring means, the signal processor being further programmed to monitor a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure read from the cavity pressure monitoring means, to determine the depth of anaesthesia or change in the depth of anaesthesia of the subject from the monitored characteristic indicative of the depth of anaesthesia, and to produce a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject.

128. An insufflator as claimed in Claim 127 in which the characteristic indicative of the depth of anaesthesia of the subject monitored by the signal processor from the signal indicative of the cavity pressure read from the cavity pressure monitoring means comprises an alternating component of the signal indicative of the cavity pressure.

129. An insufflator as claimed in Claim 128 in which the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

130. An insufflator as claimed in Claim 129 in which the signal processor is programmed to determine the depth of anaesthesia or the change in the depth of anaesthesia of the subject as a function of the pressure differential between consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure.

131. An insufflator as claimed in Claim 129 or 130 in which the signal processor is programmed to monitor the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure.

132. An insufflator as claimed in Claim 130 or 131 in which the signal processor is programmed to determine an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure as being indicative of a decrease in the depth of anaesthesia of the subject.

133. An insufflator as claimed in any of Claims 130 to 132 in which the signal processor is programmed to determine a baseline value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or a baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure, and to store the determined baseline value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the determined baseline value of the frequency in an electronic memory of the signal processor or accessible thereto.

134. An insufflator as claimed in Claim 133 in which the baseline value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure is determined by the signal processor as the value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure that corresponds with the optimum depth of anaesthesia of the subject.

135. An insufflator as claimed in Claim 133 or 134 in which an upper pressure differential increase value is stored in the electronic memory or an upper frequency increase value is stored in the electronic memory, the upper pressure differential increase value and the upper frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of a pair thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention in the anaesthesia of the subject is required, and the signal processor is programmed to compare an increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure with the corresponding one of the upper pressure differential increase value or the upper frequency increase value, and to output a warning signal in response to the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure exceeding the corresponding one of the upper pressure differential increase value or the upper frequency increase value.

136. An insufflator as claimed in any of Claims 133 to 135 in which a lower pressure differential increase value is stored in the electronic memory or a lower frequency increase value is stored in the electronic memory, the lower pressure differential increase value and the lower frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of a pair thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention of an anaesthetist should be considered, and the signal processor is programmed to compare an increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure with the corresponding one of the lower pressure differential increase value or the lower frequency increase value, and to output an alert signal in response to the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure exceeding the corresponding one of the lower pressure differential increase value or the lower frequency increase value.

137. An insufflator as claimed in Claim 135 or 136 in which the warning signal and the alert signal are convertible to a human sensory perceptible signal.

138. An insufflator as claimed in any of Claims 130 to 137 in which the signal processor is programmed to monitor both the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure.

139. An insufflator as claimed in Claim 138 in which the signal processor is programmed to determine the depth or the change in the depth of anaesthesia of the subject as a function of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure.

140. An insufflator as claimed in any of Claims 130 to 139 in which the signal processor is programmed to produce the signal indicative of the depth of anaesthesia of the subject for conversion to a visually perceptible form.

141. An insufflator as claimed in Claim 140 in which the signal processor is programmed to produce the signal indictive of the depth of anaesthesia of the subject as a waveform.

142. An insufflator as claimed in Claim 141 in which the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of the change in the differential pressure between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time or the change in the frequency value with respect to time of the alternating component of the signal indicative of cavity pressure plotted against time.

143. An insufflator as claimed in any of Claims 130 to 142 in which the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of a combination of the change in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time and the change in the frequency value with respect to time of the alternating component of the signal indicative of the cavity pressure plotted against time.

144. An insufflator as claimed in any of Claims 127 to 143 in which a first receiving means is provided for receiving a signal indicative of the airway pressure or the peak airway pressure of the subject, and the signal processor is programmed to read the signal indicative of the airway pressure or the peak airway pressure from the first receiving means and to compare the read value of the signal indicative of the airway pressure or the peak airway pressure of the subject with a maximum safe peak airway pressure value, and the signal processor is programmed to operate the flow controller to reduce the cavity pressure in response to the read value of the signal indicative of the airway pressure or the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

145. Apparatus for monitoring the depth of anaesthesia or change in the depth of anaesthesia of a subject during a minimally invasive procedure in the peritoneal cavity of a subject or in a cavity, in a vessel or an organ within the peritoneal cavity of the subject during insufflating of the cavity to a target pressure value or a pressure value below the target pressure value, the apparatus comprising a signal processor programmed to read a signal produced by a cavity pressure monitoring means indicative of the pressure in the cavity (cavity pressure), the signal processor being programmed to monitor a characteristic indicative of the depth of anaesthesia of the subject from the signal read from the pressure sensor indicative of the cavity pressure, to determine the depth of anaesthesia or the change in the depth of anaesthesia of the subject from the monitored characteristic indicative of the depth of anaesthesia, and to produce a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject.

146. Apparatus as claimed in Claim 145 in which the characteristic indicative of the depth of anaesthesia of the subject monitored by the signal processor from the signal indicative of the cavity pressure read from the pressure sensor comprises an alternating component of the signal indicative of the cavity pressure.

147. Apparatus as claimed in Claim 146 in which the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

148. Apparatus as claimed in Claim 146 or 147 in which the signal processor is programmed to determine the depth of anaesthesia or the change in the depth of anaesthesia of the subject as a function of the pressure differential between consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure.

149. Apparatus as claimed in Claim 148 in which the signal processor is programmed to monitor the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure.

150. Apparatus as claimed in Claim 148 or 149 in which the signal processor is programmed to determine an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure as being indicative of a decrease in the depth of anaesthesia of the subject.

151. Apparatus as claimed in any of Claims 148 to 150 in which the signal processor is programmed to determine a baseline value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or a baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure, and to store the determined baseline value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the determined baseline value of the frequency in an electronic memory of the signal processor or accessible thereto.

152. Apparatus as claimed in any of Claims 148 to 151 in which the baseline value of the pressure differential between the consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure is determined by the signal processor as the value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure that corresponds with the optimum depth of anaesthesia of the subject.

153. Apparatus as claimed in Claim 151 or 152 in which an upper pressure differential increase value is stored in the electronic memory or an upper frequency increase value is stored in the electronic memory, the upper pressure differential increase value and the upper frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention in the anaesthesia of the subject is required, and the signal processor is programmed to compare an increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure with the corresponding one of the upper pressure differential increase value or the upper frequency increase value, and to output a warning signal in response to the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure exceeding the corresponding one of the upper pressure differential increase value or the upper frequency increase value.

154. Apparatus as claimed in any of Claims 151 to 153 in which a lower pressure differential increase value is stored in the electronic memory or a lower frequency increase value is stored in the electronic memory, the lower pressure differential increase value and the lower frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention of an anaesthetist should be considered, and the signal processor is programmed to compare an increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure with the corresponding one of the lower pressure differential increase value or the lower frequency increase value, and to output an alert signal in response to the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure exceeding the corresponding one of the lower pressure differential increase value or the lower frequency increase value.

155. Apparatus as claimed in Claim 153 or 154 in which the warning signal and the alert signal are convertible to a human sensory perceptible signal.

156. Apparatus as claimed in any of Claims 148 to 155 in which the signal processor is programmed to monitor both the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure.

157. Apparatus as claimed in Claim 156 in which the signal processor is programmed to determine the depth or the change in the depth of anaesthesia of the subject as a function of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure.

158. Apparatus as claimed in any of Claims 148 to 157 in which the signal processor is programmed to produce the signal indicative of the depth of anaesthesia of the subject for conversion to a visually perceptible signal.

159. Apparatus as claimed in Claim 158 in which the signal processor is programmed to produce the signal indictive of the depth of anaesthesia of the subject as a waveform.

160. Apparatus as claimed in Claim 159 in which the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of the change in the differential pressure between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time or the change in the frequency value with respect to time of the alternating component of the signal indicative of cavity pressure plotted against time.

161. Apparatus as claimed in any of Claims 148 to 160 in which the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of a combination of the change in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time and the change in the frequency value with respect to time of the alternating component of the signal indicative of the cavity pressure plotted against time.

162. A method for insufflating the peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject, the method comprising delivering insufflating gas to the cavity, monitoring the pressure in the cavity (cavity pressure), monitoring the airway pressure of the subject during insufflating of the cavity, comparing the airway pressure of the subject with a maximum safe airway pressure value, and reducing the cavity pressure by reducing or temporarily terminating the supply of insufflating gas to the cavity in response to the airway pressure of the subject exceeding the maximum safe airway pressure value.

163. A method as claimed in Claim 162 in which the maximum safe airway pressure value is stored as a maximum safe peak airway pressure value.

164. A method as claimed in Claim 163 in which the peak airway pressure of the subject is determined from the monitored airway pressure of the subject, or the airway pressure of the subject monitored is the peak airway pressure of the subject.

165. A method as claimed in any of claims 162 to 164 in which the cavity pressure is reduced by venting or withdrawing insufflating gas from the cavity.

166. A method as claimed in Claim 165 in which the insufflating gas is withdrawn from the cavity by applying a vacuum to the cavity.

167. A method as claimed in any of Claims 162 to 166 in which the cavity pressure is reduced in incremental pressure reducing steps in response to the airway pressure of the subject exceeding the maximum safe airway pressure value.

168. A method as claimed in Claim 167 in which the cavity pressure is maintained substantially constant at the current reduced cavity pressure value for a predefined dwell time interval each time the cavity pressure is reduced by one of the incremental pressure reducing steps.

169. A method as claimed in Claim 167 or 168 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is the same as the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

170. A method as claimed in Claim 167 or 168 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is greater than or less than the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

171. A method as claimed in Claim 170 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step plus the incremental pressure value by which the cavity pressure is reduced during the first one of the incremental pressure reducing steps.

172. A method as claimed in Claim 170 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value lying in the range of 1.5 times to 3 times the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

173. A method as claimed in Claim 172 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value of approximately twice the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

174. A method as claimed in any of Claims 168 to 173 in which each predefined dwell time interval lies in the range of 0.5 minutes to 2 minutes, and preferably, each predefined dwell time interval lies in the range of 0.75 minutes to 1.5 minutes, and advantageously, each predefined dwell time interval is approximately 1 minute.

175. A method as claimed in any of Claims 169 to 174 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps lies in the range of 0.5mmHg to 2mmHg.

176. A method as claimed in any of Claims 169 to 175 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps is approximately 1 mmHg.

177. A method as claimed in any of Claims 162 to 176 in which the cavity pressure is reduced until the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

178. A method as claimed in Claim 177 in which if the cavity pressure is reduced to a predefined minimum cavity pressure before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, delivery of insufflating gas to the cavity is terminated.

179. A method as claimed in Claim 178 in which the cavity pressure is maintained at a reduced cavity pressure corresponding to the cavity pressure at which the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value or at the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

180. A method as claimed in Claim 178 or 179 in which a warning signal convertible to a human sensory perceptible signal is produced in response to the cavity pressure being reduced to the predefined minimum cavity pressure value.

181. A method as claimed in any of Claims 178 to 180 in which the predefined minimum cavity pressure value is a cavity pressure value consistent with producing a minimum working volume in the cavity.

182. A method as claimed in any of Claims 178 to 181 in which the predefined minimum cavity pressure value lies in the range of 3mmHg to 8mmHg, and preferably, the predefined minimum cavity pressure value is approximately 5mmHg.

183. A method as claimed in any of Claims 162 to 182 in which the signal indicative of the airway pressure or the peak airway pressure of the subject is derived from one of a pressure sensor adapted to monitor the airway pressure of the subject, a pressure sensor of an anaesthesia control and monitoring machine, or a pressure sensor located in a ventilator configured for ventilating the subject.

184. A method as claimed in any of Claims 162 to 183 in which the cavity pressure is maintained at a target pressure value until the peak airway pressure of the subject exceeds the maximum safe peak airway pressure value.

185. A method as claimed in any of Claims 162 to 184 in which the rate at which the cavity is being insufflated is determined and is compared with a maximum insufflating rate value, and the rate at which the cavity is being insufflated is reduced in response to the rate at which the cavity is being insufflated exceeding the maximum insufflating rate value.

186. A method as claimed in Claim 185 in which the maximum insufflating rate value is defined as a function of cavity pressure.

187. A method as claimed in Claim 186 in which the rate at which the cavity is being insufflated is determined as a function of the cavity pressure.

188. A method as claimed in any of Claims 185 to 187 in which the maximum insufflating rate value is defined as a value of a maximum increase in cavity pressure per unit time.

189. A method as claimed in Claim 188 in which the rate at which the cavity is being insufflated is determined as the increase in the cavity pressure per unit time.

190. A method as claimed in any of Claims 185 to 189 in which the maximum insufflating rate value is defined as a function of the flow of the insufflating gas delivered to the cavity.

191. A method as claimed in Claim 190 in which the rate at which the cavity is being insufflated is determined as a function of the flow at which the insufflating gas is being delivered to the cavity.

192. A method as claimed in any of Claims 185 to 191 in which the maximum insufflating rate value is defined as a value of a maximum rate of delivery of insufflating gas to the cavity.

193. A method as claimed in Claim 192 in which the rate at which the cavity is being insufflated is determined as the flow rate at which the insufflating gas is being delivered to the cavity.

194. A method as claimed in any of Claims 185 to 193 in which a plurality of maximum insufflating rate values are defined for respective subjects of different types.

195. A method as claimed in any of Claims 185 to 194 in which a plurality of maximum insufflating rate values are defined for subjects of one or more of different ages or different age ranges, of different weights or different weight ranges, of different body mass indices or different body mass index ranges, or of different sexes.

196. A method as claimed in any of Claims 185 to 195 in which a plurality of maximum insufflating rate values are defined for different cavities of the respective different subjects.

197. A method as claimed in any of Claims 185 to 196 in which a plurality of maximum insufflating rate values are defined for the peritoneal cavity of the respective different types of subjects.

198. A method as claimed in any of Claims 162 to 197 in which a characteristic indicative of the performance of the heart of the subject is determined and compared with a predefined minimum value of a characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall and/or a predefined maximum value of a characteristic indicative of maximum performance value above which the performance of a heart of a subject should not exceed, and delivery of insufflating gas to the cavity is paused or terminated or insufflating gas is withdrawn or vented from the cavity in response to the value of the characteristic indicative of the performance of the heart of the subject falling below the predefined minimum value of the characteristic, or rising above the predefined maximum value of the characteristic.

199. A method as claimed in Claim 198 in which the predefined minimum value of the characteristic indicative of the performance of the heart of the subject comprises a minimum value of the heart rate of a subject below which the heart rate of a subject should not fall, the characteristic indicative of the performance of the heart of the subject is determined as the heart rate of the subject.

200. A method as claimed in Claim 198 or 199 in which the predefined maximum value of the characteristic indicative of the performance of the heart of the subject comprises a maximum value of the heart rate of a subject above which the heart rate of a subject should not exceed, and the characteristic indicative of the performance of the heart of the subject is determined as the heart rate of the subject.

201. A method as claimed in any of Claims 198 to 200 in which the characteristic indictive of the performance of the heart of a subject is determined from a signal from a heart performance monitoring means.

202. A method as claimed in any of Claims 198 to 201 in which the characteristic indicative of the performance of the heart of a subject is determined from a heart rate monitoring means.

203. A method for insufflating the peritoneal cavity, or a cavity in a vessel or organ in the peritoneal cavity, the method comprising delivering insufflating gas to the cavity, monitoring the pressure in the cavity (cavity pressure) by a pressure sensor adapted to produce a signal indicative of the cavity pressure, controlling delivery of insufflating gas to the cavity in response to the signal indicative of the cavity pressure to maintain the cavity pressure at a target pressure value or a pressure value below the target pressure value, monitoring a characteristic indicative of the depth of anaesthesia of the subject from (he signal indicative of the cavity pressure, and producing a human sensory perceptible signal indicative of the depth of anaesthesia or change in the depth of anaesthesia of the subject.

204. A method as claimed in Claim 203 in which the characteristic indicative of the depth of anaesthesia of the subject monitored from the signal indicative of the cavity pressure produced by the pressure sensor comprises an alternating component of the signal indicative of the cavity pressure.

205. A method as claimed in Claim 204 in which the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm of the subject separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

206. A method as claimed in Claim 204 or 205 in which the depth of anaesthesia or the change in the depth of anaesthesia of the subject is determined as a function of the pressure differential between the consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure.

207. A method as claimed in Claim 206 in which the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure is monitored.

208. A method as claimed in Claim 206 or 207 in which an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure is determined as being indicative of a decrease in the depth of anaesthesia of the subject.

209. A method as claimed in any of Claims 206 to 208 in which a baseline value of the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or a baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure is determined.

210. A method as claimed in Claim 209 in which the baseline value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure is determined as the value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure that corresponds with the optimum depth of anaesthesia of the subject.

211. A method as claimed in Claim 209 or 210 in which the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure is compared with an upper pressure differential increase value or an upper frequency increase value, the upper pressure differential increase value and the upper frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention by an anaesthetist in the anaesthesia of the subject is required, and a warning signal is produced in response to either the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof exceeding the corresponding one of the upper pressure differential increase value or the upper frequency increase value.

212. A method as claimed in any of Claims 209 to 211 in which the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure is compared with a lower pressure differential increase value or a lower frequency increase value, the lower pressure differential increase value and the lower frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention by an anaesthetist in the anaesthesia of the subject should be considered, and an alert signal is produced in response to either the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof exceeding the corresponding one of the lower pressure differential increase value or the lower frequency increase value.

213. A method as claimed in Claim 211 or 212 in which the warning signal and the alert signal are convertible to a human sensory perceptible signal.

214. A method as claimed in any of Claims 206 to 213 in which both the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure are monitored.

215. A method as claimed in Claim 214 in which the depth of anaesthesia or the change in the depth of anaesthesia of the subject is determined as a function of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure.

216. A method as claimed in any of Claims 203 to 215 in which the signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject is adapted for conversion to a visually perceptible signal.

217. A method as claimed in any of Claims 206 to 216 in which the signal indictive of the depth of anaesthesia of the subject is produced as a waveform.

218. A method as claimed in Claim 217 in which the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of the change in the values of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time or the change in the frequency values with respect to time of the alternating component of the signal indicative of cavity pressure plotted against time.

219. A method as claimed in Claim 217 or 218 in which the waveform indicative of the depth of anaesthesia of the subject comprises an inverted plot of a combination of the change in the values of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof with respect to time and the change in the frequency values with respect to time of the alternating component of the signal indicative of the cavity pressure plotted against time.

220. A method as claimed in any of Claims 203 to 219 in which the peak airway pressure of the subject is monitored during insufflating of the cavity of the subject and compared with a maximum safe peak airway pressure value, and the cavity pressure is reduced by reducing or temporarily terminating the supply of insufflating gas to the cavity or by venting or withdrawing insufflating gas from the cavity in response to the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

221. A method for monitoring the depth of anaesthesia or change in the depth of anaesthesia of a subject during a minimally invasive procedure in the peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity in which the cavity is being insufflated to a target pressure value or a pressure value below the target pressure value, the method comprising monitoring a signal indicative of the pressure in the cavity (cavity pressure), monitoring a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure, determining the depth of anaesthesia or the change in the depth of anaesthesia of the subject from the monitored characteristic, and producing a signal indicative of the depth of anaesthesia or change in the depth of anaesthesia of the subject.

222. A method as claimed in Claim 221 in which the characteristic indicative of the depth of anaesthesia of the subject monitored from the signal indicative of the cavity pressure comprises an alternating component of the signal indicative of the cavity pressure.

223. A method as claimed in Claim 222 in which the alternating component of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm of the subject separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

224. A method as claimed in Claim 222 or 223 in which the depth of anaesthesia or the change in the depth of anaesthesia of the subject is determined as a function of the pressure differential between the consecutive upper and lower peak values or the frequency of the alternating component of the signal indicative of the cavity pressure.

225. A method as claimed in Claim 224 in which the pressure differential between the consecutive upper and lower peak values of consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure is monitored.

226. A method as claimed in Claim 224 or 225 in which an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure is determined as being indicative of a decrease in the depth of anaesthesia of the subject.

227. A method as claimed in any of Claims 224 to 226 in which a baseline value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or a baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure is determined.

228. A method as claimed in Claim 227 in which the baseline value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the baseline value of the frequency of the alternating component of the signal indicative of the cavity pressure is determined as the value of the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or the frequency of the alternating component of the signal indicative of the cavity pressure that corresponds with the optimum depth of anaesthesia of the subject.

229. A method as claimed in Claim 227 or 228 in which the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure is compared with an upper pressure differential increase value or an upper frequency increase value, the upper pressure differential increase value and the upper frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention by an anaesthetist in the anaesthesia of the subject is required, and a warning signal is produced in response to either the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof exceeding the corresponding one of the upper pressure differential increase value or the upper frequency increase value.

230. A method as claimed in any of Claims 227 to 229 in which the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or the increase in the current value of the frequency above the baseline value thereof of the alternating component of the signal indicative of the cavity pressure is compared with a lower pressure differential increase value or a lower frequency increase value, the lower pressure differential increase value and the lower frequency increase value being respective values of an increase in the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof or an increase in the frequency of the alternating component of the signal indicative of the cavity pressure above the corresponding baseline value thereof, corresponding to a minimum permissible decrease in the depth of anaesthesia of a subject from the optimum value thereof below which intervention by an anaesthetist in the anaesthesia of the subject should be considered, and an alert signal is produced in response to either the increase in the current value of the pressure differential between the consecutive upper and lower peak values of the current pair thereof above the baseline value thereof or an increase in the current value of the frequency above the baseline value thereof exceeding the corresponding one of the lower pressure differential increase value or the lower frequency increase value.

231. A method as claimed in Claim 229 or 230 in which the warning signal and the alert signal are convertible to a human sensory perceptible signal.

232. A method as claimed in any of Claims 224 to 231 in which both the pressure differential between the consecutive upper and lower peak values of the consecutive pairs thereof and the frequency of the alternating component of the signal indicative of the cavity pressure are monitored.

233. A method as claimed in Claim 232 in which the depth of anaesthesia or the change in the depth of anaesthesia of the subject is determined as a function of the pressure differential between the consecutive upper and lower peak values and the frequency of the alternating component of the signal indicative of the cavity pressure.

234. A method for insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject by an insufflator, the insufflator comprising: a flow controller for controlling the delivery of insufflating gas to the cavity, a first receiving means for receiving a signal indicative of airway pressure in the airway of the subject, and a stored maximum safe airway pressure value, the method comprising reading the value of the signal indicative of the airway pressure of the subject from the first receiving means, comparing the read value of the signal indicative of the airway pressure of the subject with the stored maximum safe airway pressure value, and operating the flow controller to reduce the pressure in the cavity (cavity pressure) in response to the read value of the signal indicative of the airway pressure of the subject exceeding the maximum safe airway pressure value.

235. A method as claimed in Claim 234 in which the maximum safe airway pressure value is stored as a maximum safe peak airway pressure value.

236. A method as claimed in Claim 235 in which the peak airway pressure of the subject is determined from the monitored airway pressure of the subject, or the airway pressure of the subject monitored is the peak airway pressure of the subject.

237. A method as claimed in any of claims 234 to 236 in which the flow controller is operated to reduce the cavity pressure by reducing the rate of delivery of insufflating gas to the cavity.

238. A method as claimed in any of claims 234 to 237 in which the flow controller is operated to reduce the cavity pressure by temporarily terminating delivery of insufflating gas to the cavity.

239. A method as claimed in any of Claims 234 to 238 in which the insufflator comprises a pressure reducing means configured to reduce the cavity pressure, and the pressure reducing means is operated for reducing the cavity pressure in response to the read value of the signal indicative of the peak airway pressure of the subject exceeding the maximum safe peak airway pressure value.

240. A method as claimed in Claim 239 in which the pressure reducing means comprises a venting means for venting the cavity.

241. A method as claimed in Claim 240 in which the venting means comprises a venting valve.

242. A method as claimed in any of Claims 239 to 241 in which the pressure reducing means comprises a vacuum applying means for applying a vacuum to the cavity, and preferably, the vacuum applying means comprises one of either a vacuum pump or a communicating means for selectively communicating the cavity with a vacuum source.

243. A method as claimed in Claim 242 in which the communicating means comprises an isolating valve alternately operable in a communicating state communicating the cavity with the vacuum source, and in an isolating state isolating the cavity from the vacuum source.

244. A method as claimed in any of Claims 234 to 243 in which the flow controller and/or the pressure reducing means are operated to reduce the cavity pressure in incremental pressure reducing steps in response to the read value of the signal indicative of the peak airway pressure in the subject exceeding the maximum safe peak airway pressure value.

245. A method as claimed in Claim 244 in which the flow controller and/or the pressure reducing means are operated for maintaining the cavity pressure substantially constant at the current reduced cavity pressure value for a predefined dwell time interval each time the cavity pressure is reduced by one of the incremental pressure reducing steps.

246. A method as claimed in Claim 244 or 245 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is the same as the incremental pressure value by which the cavity pressure was reduced during the immediately preceding incremental pressure reducing step.

247. A method as claimed in Claim 244 or 245 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is greater than or less than the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

248. A method as claimed in Claim 247 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step plus the value by which the cavity pressure is reduced during the first one of the incremental pressure reducing steps.

249. A method as claimed in Claim 247 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value lying in the range of 1.5 times to 3 times the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

250. A method as claimed in Claim 249 in which the incremental pressure value by which the cavity pressure is reduced in each incremental pressure reducing step is equal to a pressure value of approximately twice the incremental pressure value by which the cavity pressure is reduced in the immediately preceding incremental pressure reducing step.

251. A method as claimed in any of Claims 245 to 250 in which each predefined dwell time interval lies in the range of 0.5 minutes to 2 minutes.

252. A method as claimed in any of Claims 245 to 251 in which each predefined dwell time interval lies in the range of 0.75 minutes to 1.5 minutes.

253. A method as claimed in any of Claims 245 to 252 in which each predefined dwell time interval is approximately 1 minute.

254. A method as claimed in any of Claims 244 to 253 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps lies in the range of 0.5mmHg to 2mmHg.

255. A method as claimed in any of Claims 244 to 254 in which the incremental pressure value by which the cavity pressure is reduced in the first one of the incremental pressure reducing steps is approximately tmmHg.

256. A method as claimed in any of Claims 234 to 255 in which the flow controller and/or the pressure reducing means is operated to reduce the cavity pressure until the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

257. A method as claimed in Claim 256 in which the flow controller and/or the pressure reducing means are operated to cease reducing the cavity pressure below a predefined minimum cavity pressure if the cavity pressure is reduced to the predefined minimum cavity pressure before the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value.

258. A method as claimed in Claim 257 in which the flow controller and/or the pressure reducing means are operated to maintain the cavity pressure at a reduced current cavity pressure value corresponding to the cavity pressure value at which the read value of the signal indicative of the peak airway pressure of the subject is reduced to or below the maximum safe peak airway pressure value, or the predefined minimum cavity pressure value if the cavity pressure is reduced thereto before the peak airway pressure of the subject is reduced to the maximum safe peak airway pressure value.

259. A method as claimed in Claim 257 or 258 in which a warning signal convertible to a human sensory perceptible signal warning that the cavity pressure has been reduced to the predefined minimum cavity pressure value is produced in response to the cavity pressure being reduced to the predefined minimum cavity pressure value.

260. A method as claimed in any of Claims 257 to 259 in which the predefined minimum cavity pressure value comprises a cavity pressure value consistent with producing a minimum working volume in the cavity.

261. A method as claimed in any of Claims 257 to 260 in which the predefined minimum cavity pressure value lies in the range of 3mmHg to 8mmHg.

262. A method as claimed in any of Claims 257 to 261 in which the predefined minimum cavity pressure value is approximately 5mmHg.

263. A method as claimed in any of Claims 234 to 262 in which the insufflator comprises an insufflating monitoring means for monitoring insufflating of the cavity and for producing a signal indicative of the insufflating of the cavity, the method further comprises reading the signal produced by the insufflating monitoring means indicative of the insufflating of the cavity, determining the rate at which the cavity is being insufflated from the signal read from the insufflating monitoring means, comparing the determined rate at which the cavity is being insufflated with a stored maximum insufflating rate value, and operating the flow controller to prevent the rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

264. A method as claimed in Claim 263 in which the flow controller is operated to reduce the flow rate at which insufflating gas is being delivered to the cavity or to temporarily pause delivery of insufflating gas to the cavity in response to the determined rate at which the cavity is being insufflated exceeding the stored maximum insufflating rate value.

265. A method as claimed in Claim 263 or 264 in which the insufflating monitoring means for monitoring insufflating of the cavity comprises a cavity pressure monitoring means adapted to monitor the cavity pressure and to produce a signal indicative of the cavity pressure.

266. A method as claimed in any of Claims 263 to 265 in which the stored maximum insufflating rate value is stored as a function of cavity pressure, and the rate at which the cavity is being insufflated is determined as a function of the cavity pressure.

267. A method as claimed in any of Claims 263 to 266 in which the stored maximum insufflating rate value is stored as a value of a maximum increase in cavity pressure per unit time, and the rate at which the cavity is being insufflated is determined as the increase in the cavity pressure per unit time.

268. A method as claimed in any of Claims 263 to 267 in which the insufflating monitoring means comprises a flow sensor for monitoring the flow of insufflating gas to the cavity and for producing a signal indicative of the flow of insufflating gas to the cavity.

269. A method as claimed in any of Claims 263 to 268 in which the stored maximum insufflating rate value is stored as a function of the flow of the insufflating gas delivered to the cavity, and the rate at which the cavity is being insufflated is determined as a function of the flow rate at which the insufflating gas is being delivered to the cavity.

270. A method as claimed in any of Claims 263 to 269 in which (he stored maximum insufflating rate value is stored as a value of a maximum rate of delivery of insufflating gas to the cavity, and the rate at which the cavity is being insufflated is determined as the flow rate at which the insufflating gas is being delivered to the cavity.

271. A method as claimed in any of Claims 263 to 270 in which a plurality of maximum insufflating rate values are stored for respective subjects of different types.

272. A method as claimed in any of Claims 263 to 271 in which a plurality of maximum insufflating rate values are stored for subjects of one or more of different ages or different age ranges, of different weight or different weight ranges, of different body mass indices or different body mass index ranges, or of different sexes.

273. A method as claimed in any of Claims 263 to 272 in which a plurality of maximum insufflating rate values are stored for different cavities of the respective different subjects.

274. A method as claimed in any of Claims 234 to 273 in which a predefined minimum value of a characteristic indicative of a minimum performance value below which the performance of a heart of a subject should not fall or a predefined maximum value of a characteristic indicative of the maximum performance value above which the performance of a heart of a subject should not exceed are stored and the method further comprises reading a value of a signal indicative of a characteristic of the performance of the heart of the subject, comparing the read value of the characteristic of the performance of the heart of the subject with the stored predefined minimum value of the characteristic or the stored maximum value of the characteristic, and operating the insufflator to one of reduce the rate of delivery of insufflating gas to the cavity, or to cease delivery of insufflating gas to the cavity, or to operate the pressure reducing means to reduce the cavity pressure in response to the read value of the signal indicative of the characteristic of the performance of the heart of the subject falling below the stored predefined minimum value of the characteristic, or exceeding the stored predefined maximum value of the characteristic.

275. A method as claimed in any of Claims 234 to 274 in which a characteristic indicative of the depth of anaesthesia or a change in the depth of anaesthesia of the subject is monitored from the signal indicative of the cavity pressure, and a signal indicative of the depth of anaesthesia or a change in the depth of anaesthesia of the subject is produced.

276. A method as claimed in Claim 275 in which the characteristic indicative of the depth of anaesthesia of the subject monitored from the signal indicative of the cavity pressure produced by the pressure sensor comprises an alternating component of the signal indicative of the cavity pressure.

277. A method as claimed in Claim 276 in which the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm of the subject separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of ventilating of or breathing by the subject.

278. A method for operating an insufflator insufflating a peritoneal cavity or a cavity in a vessel or organ in the peritoneal cavity of a human or animal subject for determining the depth of anaesthesia or a change in the depth of anaesthesia of the subject, the insufflator comprising a cavity pressure monitoring means for monitoring pressure in the cavity and producing a signal indicative of the cavity pressure, the method comprising reading the signal indicative of the cavity pressure produced by the cavity pressure monitoring means, monitoring a characteristic indicative of the depth of anaesthesia of the subject from the signal indicative of the cavity pressure read from the cavity pressure monitoring means, determining the depth of anaesthesia or change in the depth of anaesthesia of the subject from the monitored characteristic indicative of the depth of anaesthesia, and producing a signal indicative of the depth of anaesthesia or the change in the depth of anaesthesia of the subject.

279. A method as claimed in Claim 278 in which the characteristic indicative of the depth of anaesthesia of the subject monitored from the signal indicative of the cavity pressure read from the cavity pressure monitoring means comprises an alternating component of the signal indicative of the cavity pressure.

280. A method as claimed in Claim 279 in which the alternating component of the signal indicative of the cavity pressure comprises an alternating pressure component induced in the cavity pressure by movement of the diaphragm separating the peritoneal cavity from the thoracic cavity towards and away from the peritoneal cavity as a result of Il l ventilating of or breathing by the subject.

281. Use of the insufflators as claimed in any of Claims 1 to 144 in insufflating a peritoneal cavity of a subject or insufflating a cavity in a vessel or an organ in the peritoneal cavity of the subject.