GB2209950A - Scavenging systems - Google Patents

Abstract

A scavenging system, suitable for use in dental surgeries and clinics, includes a scavenging mask comprising an outer mask 12 and an inner mask 11 spaced therefrom, means 11' being provided for delivery of anaesthetic gas mixture to the interior of the inner mask and means 12' for continuously scavenging the space between the masks. A one-way valve 14 links the inner mask to the space between the masks. <IMAGE>

Description

IMPROVEMENTS IN OR RELATING TO SCAVENGING SYSTEMS The present invention concerns improvements in or relating to scavenging systems. More particularly, the present invention concerns a system for the scavenging of anaesthetic gas pollutants utilised in conjunction with dental procedures. The scavenging system of the present invention was particularly developed for use in dental surgeries and clinics.

The scavenging of anaesthetic gas pollutants when patients are undergoing dental operations in a dental surgery, when subjected to either general anaesthesia or relative analgesia, presents inherent problems, mainly as a result of the required access by the dentist to the mouth of the patient. As a result of the mouth of the patient having to be kept clear, any oral exhalation by the patient will result in a release of pollutants into the dental surgery. There is also the additional problem that anaesthetic gas pollutants can inadvertently be released from around the mask as a result of a poor fit on to the patients face.

It is known at present that concentrations of anaesthetic gas pollutants, in particular nitrous oxide, can exceed values of 1500 ppm for significant periods in close proximity to the patient and hence the breathing zone of the dentist, the dental assistant and for the anaesthetist (the latter during the use of general anaesthe#ia), while the concentration within the surgery remote from the patient is likely to exceed 1000 ppm.

As a result of the routes in which the pollutant can enter the dental surgery, it was felt that any scavenging system must contain a scavenging nasal mask to remove pollutants prior to their entry into the dental surgery, and preferably an extraction means to remove pollutants that are orally exhaled or that have escaped capture by the mask. We have now produced a scavenging mask suitable for use during dental procedures, suitably with a local extracting arrangement to comply with the above requirements.

According to the present invention there is provided a scavenging system, suitable for use in dental surgeries and clinics, said system including a scavenging mask comprising an outer mask member and an inner mask member, the inner member being located within the outer member and spaced therefrom,means being provided for delivery of anaesthetic gas mixture to the interior of the inner mask member and means for continuously scavenging the space between the inner mask member and the outer mask member, a one-way valve means also being provided for linking the inner mask member to the space between the two mask members.

The means for delivering anaesthetic gas mixture to the interior of the inner mask member preferably comprises two tubes attached to the inner mask, the free ends of said tubes terminating outside of the outer mask member. The outer mask member is also preferably provided with two tube members for effecting continual scavenging of the space between the inner mask member and the outer mask member.

The scavenging system may also include an extraction means having inlets positioned either side of where the patient will rest his or her head.

The scavenging system of the present invention may also include means to esiabl scavenging to take place from within the inner mask member. Such scavenging is appropriately effected by the presence of a pressure relief valve which opens as the patient exhales.

It wili thus be seen that the mask is a double skinned mask with a one way valve linking the inner mask to the space between the two masks. Each mask has two tube attachments both of which terminate outside of the outer mask. The tubes to the inner mask are used to deliver the anaesthetic gas mixture to the patient while the tubes to the outer mask are scavenged continually.

The mask is designed for use during both relative analgesia and general anaesthesia with only a change in the valve arrangement being required. An additional adjustable valve arrangement is used during general anaesthesia, which enables the anaesthetist some control over the pressure of anaesthetic gas inside the inner mask. Such additional valve arrangement extends through an opening in the outer shell of the mask. When used for relative analgesia the additional valve arrangement is not required. Accordingly, the opening in the outer shell is closed by utilising a transparent plug which enables the dentist to see that the one-way valve is working correctly and that the patient is breathing as required i.e. through the nose.

The scavenging system may also include a local extraction means having inlets positioned either side of where the patients rest their head. The air velocity at the inlet of the local extraction means is of the same order of magnitude for both relative analgesia and general anaesthesia.

When a patient is being treated on a dental chair, such chair includes a head-rest which includes the required local extraction means whilst maintaining the operating mechanism associated with the dental chair.

During relative analgesia, music may be introduced into the chair by the installation of two small speakers inside the headrest. A cable then connects the speakers to a conveniently placed personal cassette recorder and the decision to listen to music can then be made at the discretion of the patient. Such arrangement provides a more relaxing environment to patients, many of whom are nervous of being given dental treatment. For some instances of general anaesthesia, treatment may be carried out in a hospital in which the patient was treated in the supine position on a trolley. In this instance a local extraction means would be built into the trolley at the position in which the head of the patient would rest.

The present invention will be further illustrated by way of example, with reference to the accompanying drawings in which: Fig. 1 is a cross-section through a scavenging mask in accordance with the present invention for use during general anaesthesia; Fig. Z schemåtically illustrates a suitable local extraction means for use in the scavenging system of the present invention; rigs. 3 - 7 are graphs representing the concentration of nitrous oxide in a dental clinic during the utilisation of either relative analgesia or general anaesthesia, Fig. 3 being a control graph; and Figs. 8,-9 and 10 schematically illustrate a scavenging mask in accordance with the present invention.

As illustrated in Fig. 1, the scavenging mask consists of an inner shell 11 and an outer shell 12. Each of the shells are constructed of silicone rubber and contain two tube attachments 11, 12', all of which have a bore of lOmm. The two shells 11, 12 of the mask are concentric and have a small space 13 between them. Such space varies in width between 1.5mm and 7 mm as indicated. The tube attachments 11t of the inner mask 11 penetrate the outer mask 12 via two holes on opposite sides of the outer mask 12. The holes through which the tube attachments 11' of the inner mask 11 pass are sized to be a close fit to the upper mentioned tube attachments 11'.

The inner and outer masks 11, 12 are connected by a one-way valve 14 which operates when the patient exhales through the nose. Waste anaesthetic gas from the inner mask 11 is transferred to the space 13 and captured by the scavenge flow from the outer mask 12. The scavenge flow rate from the outer mask 12 is designed to be between 60 1/mien and 90 1/mien. The lower value is designed for use during relative analgesia while the upper limit is designed for use during general anaesthesia where higher flow rates of nitrous oxide are generally used and an anaesthetist is present.

The scavenging mask in accordance with the present invention may be utilised to incorporate "passive" scavenging from the inner mask 11. This operates by the presence of a pressure relief valve (not shown) which opens as the patient exhales. A very low flow rate is applied from the inner mask 11. Such procedure has, however, been found to be inappropriate for use during general anaesthesia, but has been found to be quite suitable for use during relative analgesia. The flow rate is generally expected to be 10 1/mien., during exhalation.

The valve used in the mask depends upon whether it is being used for either general anaesthesia or relative analgesia. The mask itself can be used for either type of sedation.

The mask illustrated in Fig. 1 is suitable for use for the administration of general anaesthetic. In such case an adjustable valve 15 is utilised, which valve links the inner and outer mask 11 and 12 and also penetrates the outer mask 12. An adjusting screw 16 is located on top of the valve 15 to enable the anaesthetist to increase the pressure within the inner mask 11.

During relative analgesia, the patient is conscious and the dentist is unlikely to require the ability of increasing or decreasing the pressure within the inner mask 11. In such case, a one-way valve 14 is provided the body of which is slightly smaller than that used for general anaesthesia and does not protrude through the outer mask.

In such case, the hole in the outer mask is closed off by a transparent plug. Use of the transparent plug is so that the dentist can see that the valve 14 is operating correctly.

Whilst the valves have been designed for specific purposes, there is no reason why they cannot be interchanged depending upon the dentist and/or anaesthetist using them.

The mask in component form is illustrated in Fig.8 and Figs. 9 and 10 show the mask in the manner in which it would be used. The valve shown is that used for general anaesthesia.

The local extraction means utilised depend upon whether the patient has been subjected to either general anaesthesia or relative analgesia. However, the basic design of the extraction means utilised is the same.

During general anaesthesia, clinical trials were conducted in a hospital in which operations were carried out on a trolley. As shown in Fig. 2, a plenum box 21 was located below the backrest 28 of the trolley and the inlets 22,23 protruded through the backrest 24 and the cushion. In this case, the plenum box 21 and inlets 22, 23 were movable so as to obtain the most suitable position. The inlets for this local extraction means were both 65 mm x 65 mm with a total flow rate of approximately 33 1/sec. Such arrangement resulted in a capture velocity of approximately 3.9 m/sec.

During the use of relative analgesia, the dental operations were carried out on a typical dental chair.

To accommodate the local extraction means, a slightly larger headrest would be built which includes two air inlets.

The headrest of the chair itself would form the plenum box. The outlet of the plenum box emerges at the back of the headrest with the associated flexible ducting being attached to the back of the chair. The inlets of this local extraction means were both approximately 60 mm x 75 mm with a total extract air flow rate of 30 1/sec. This resulted in a face velocity of 2.5 m/sec. The inlets of this device were not absolutely square but tended to follow the shape of the headrest. Two speakers were installed into the headrest to enable music to be played to the patient. In practice, an air flow rate of 40 1/sec.

would be more suitable assuming that the noise level would be maintained at a low level.

The scavenging equipment in accordance with the present invention has been utilised on a number of occasions during the utilisation of either relative analgesia or general anaesthesia. At the time the scavenging equipment was being used, the levels of nitrous oxide within the surgery were monitored. These concentrations of nitrous oxide were compared with the levels that were measured when the equipment was not used. The accompanying to to to 7 depict the levels that were measured.

Fig. 3 shows the levels of nitrous oxide during relative analgesia without any scavenging. Figs. 4 and 5 depict the concentration of nitrous oxide measured during the administration of relative analgesia using scavenging equipment in accordance with the present invention. Figs.6 and 7 to depict measurement carried out during the administration of a general anaesthetic. Included in these Figs. are the effects of not using equipment in accordance with the invention.

It is believed that the information contained in the graphs shown in Figs. 3 to 7 clearly indicate that a substantial reduction in the pollution of a dental surgery or clinic from waste anaesthetic gases can be achieved utilising the scavenging equipment in accordance with the present invention.

We would comment that, as a result of the limitations of the monitoring equipment, any concentrations exceeding 1440 ppm. are shown at 1440 ppm.

It is believed that the scavenging equipment in accordance with the present invention should provide the desired reduction in pollutant levels in dental surgeries or clinics and the like when carrying out dental procedures involving relative analgesia or general anaesthesia.

Claims (8)

1. A scavenging system, suitable for use in dental surgeries and clinics, said system including a scavenging mask comprising an outer mask member and an inner mask member, the inner member being located within the outer member and spaced therefrom, means being provided for delivery of anaesthetic gas mixture to the interior of the inner mask member and means for continuously scavenging the space between the inner mask member and the outer mask member, a one-way valve means also being provided for linking the inner mask member to the space between the two mask members.

2. A scavenging system as claimed in claim 1, in which the means for delivering anaesthetic gas mixture to the interior of the inner mask member comprises two tube members attached to the inner mask member, the free ends of said tube members terminating outside of the outer mask member.

3. A scavenging system as claimed in claim I or 2, in which the outer mask member is provided with two tube members for effecting continual scavenging of the space between the inner mask member and the outer mask member.

4. A scavenging system as claimed in claim 1, 2 or 3, further including an extraction means having inlets, in use, positioned either side of where the patient will rest his or her head.

5. A scavenging system as claimed in claim 4, in which the extraction means are located in the headrest of a dental chair or hospital trolley.

6. A scavenging system as claimed in any preceding claim, further including means to enable scavenging to take place from within the inner mask member.

7. A scavenging system as claimed in claim 6, in which scavenging is effected using a pressure relief valve which, in use, opens as the patient exhales.

8. A scavenging system substantially as hereinbefore described with reference to the accompanying drawings.