WO2015074999A1

WO2015074999A1 - A warming arrangement and a method for warming

Info

Publication number: WO2015074999A1
Application number: PCT/EP2014/074785
Authority: WO
Inventors: Jan Sternby
Original assignee: Gambro Lundia AB
Current assignee: Gambro Lundia AB
Priority date: 2013-11-22
Filing date: 2014-11-17
Publication date: 2015-05-28
Anticipated expiration: 2016-05-22
Also published as: CN104645433A

Abstract

A warming arrangement and method for a continuous renal replacement therapy system. The system comprises a blood treatment unit and a heat exchanger configured to be fluidly coupled to an effluent fluid line to transfer heat to at least one treatment fluid and/or blood. The warming arrangement further comprises a heating element configured to transfer heat to the effluent fluid, wherein the heating element is located downstream the blood treatment unit and upstream the heat exchanger. The method includes determining a control parameter based on an indicated temperature and/or flow rate, and to control the temperature of, or the power delivered to, the heating element based on the control parameter.

Description

A warming arrangement and a method for warming

Technical field of the invention

The present invention relates generally to extracorporeal blood treatment. More particularly the invention relates to a warming arrangement, a system, a disposable kit and a method for warming an effluent fluid.

Background of the invention

In dialysis treatments some heat is generally lost to the environment from the blood circulating in an extracorporeal circuit. The extracorporeal circuit comprises a bloodline and a blood treatment unit in which the blood is treated. Heat loss from the blood in the extracorporeal circuit, in time, results in cooling of the patient's body when the blood is returned to the patient. Different kinds of blood warmers exist, but they are often difficult to get efficient enough since it is important not to expose the extracorporeally circulated blood to any excess temperatures. The temperature of the extracorporeally circulated blood should not exceed 41° as the blood might be severely affected, and/or gas bubbles might be introduced into the blood.

Loss of heat from the extracorporeally circulated blood is due to diffusion of heat either to the surrounding air and/or to an effluent fluid. Effluent fluid is constituted by the dialysis fluid used in a treatment in hemodialysis (HD) mode as well as the fluid extracted in hemodiafiltration (HDF) or hemofiltration (HF) mode. Effluent fluid is sent to a drain whereby the heat diffused from the blood to the effluent fluid is lost. Treatment fluids required in treatment of a patient by continuous renal replacement therapy, hereinafter referred to as CRRT, must often be stored in a temperature which is relatively cold with respect to the patient's body

temperature. Such fluids are typically stored at temperatures ranging from 2° to 20° C in order to preserve the fluids in a state so that the function and integrity of the fluid is maintained. The continuous nature of CRRT increases the potential of heat loss from the blood circulating in the extracorporeal circuit and the patient may under certain circumstances experience a depression of body temperature. This is especially significant when the treatment fluid has a temperature lower than the extracorporeally circulated blood. For this reason it is often desirable to heat the treatment fluid to an appropriate temperature before introducing it into the patient's body to prevent any rapid decrease of the patient's body temperature. The treatment fluid may be any fluid used in the CRRT treatment, i.e. a fluid intended for dialysis, infusion, replacement or anticoagulation.

During periods of low blood flow, about 50 ml/min, the

temperature decrease is larger compared with periods of medium blood flows, in the range of 100-200 ml/min, or high blood flows, in the range of 200-300 ml/min. For this reason it is desirable in some CRRT treatments to compensate for, or to reduce, heat loss from the extracorporeally circulating blood.

To conserve some of the heat diffused from the blood to the effluent fluid a heat exchanger as disclosed in WO 2010/040819 has been developed. The heat exchanger exchanges heat from the effluent fluid to one or several treatment fluids, or to the cleaned extracorporeally circulated blood. However, with the arrangement as disclosed in WO 2010/040819, it might be difficult to return the blood temperature in the extracorporael circuit all the way to a normal body

temperature because a limited efficieny of the heat exchanger and heat loss to the surrounding air.

JP2004313303 discloses an arrangement for discontinuous CRRT treatment working in two cycles, in which, during the first cycle, no pumping of blood or treatment fluids take place in the blood treatment unit while fresh treatment fluids are transported to balancing chambers enclosed in a casing. During the second cycle these fresh treatment fluids are passed through the fluid compartment of the blood treatment unit and the blood pump is running. During the second cycle the

effluent fluid is heated before it enters the casing on the outside of the balancing chambers. The arrangement has the drawback of providing treatment during only half of the time, during the second cycle. In addition, the heat transfer from the effluent fluid to the fresh treatment fluids will be quite ineffective, since there is very little movement of the fluids in the casing and in the balancing chambers. Also, the heating of the effluent fluid can only take place during the second cycle when the effluent pump is running. Summary of the invention

It is an object of the invention to provide a warming

arrangement, a system comprising the warming arrangement, a disposable kit adapted to cooperate with the warming

arrangement and a method for warming an effluent fluid in a continuous renal replacement therapy system, in order to heat blood continuously in an extracorporeal blood line to a normal body temperature without introducing any safety risks. According to a first aspect the object is at least partly achieved with a warming arrangement for a CRRT system. The system comprises a blood treatment unit connecting a blood line for extracorporeally circulating blood and a fluid distribution circuitry comprising at least one treatment fluid line for passing treatment fluid, and an effluent fluid line for passing effluent fluid. The warming arrangement further comprises a heat exchanger configured to be fluidly coupled to the effluent fluid line and disposed in thermal relationship with the at least one treatment fluid line so as to provide for transfer of heat from the continuously pumped effluent fluid to the at least one continuously pumped treatment fluid, and/or disposed in thermal relationship with the blood line so as to provide for transfer of heat from the continuously pumped effluent fluid to the continuously pumped blood during therapy. The warming arrangement further comprises a heating element configured to transfer heat to the effluent fluid, wherein the heating element is located downstream the blood treatment unit and upstream the heat exchanger.

With the warming arrangement the effluent fluid may reach a higher temperature compared to warming by means of a heat exchanger only, and the treatment fluids and/or blood may then be warmed to a higher temperature. As the warming of the treatment fluids and/or blood is made by indirect warming, the risk for introducing unwanted bubbles due to rapid heat changes is very low. The intermediate heating media, thus the effluent fluid, will level out any rapid temperature changes of the heating element, before the heat reaches the fluids and/or blood.

With indirect warming is meant warming via an intermediate heating media, here the effluent fluid. Thus, the effluent fluid is first warmed, whereafter the warmed effluent fluid warms one or several treatment fluids and/or blood.

According to one embodiment, the warming arrangement comprises a control unit configured to control the temperature of the heating element based on a control parameter.

According to another embodiment, the control unit is

configured to receive at least one measurement signal

indicating a temperature and/or flow rate of at least one of the effluent fluid, the at least one treatment fluid and the blood in the blood line, and to determine the control

parameter based on the temperature and/or flow rate. According to a further embodiment, the control parameter is either of a parameter which makes the heating element generate an effect, or a temperature value T_he of the heating element, needed to warm the at least one of the treatment fluids to a desired temperature T_set and/or blood to a desired temperature T_SetB.

According to a still further embodiment, the control unit is configured to calculate the control parameter based on a model of the heat exchanger.

According to a further embodiment, the warming arrangement is configured to warm the at least one treatment fluid to a desired temperature T_set in an interval between 35° and 45° C, preferably between 37° and 43° C. This may be accomplished by warming the effluent fluid to a temperature between 37° and 55° C, preferably 40° to 50° C before the effluent fluid enters the heat exchanger. According to one embodiment, the heating element comprises at least one heating plate configured to warm the effluent fluid in the effluent fluid line. The heating element may then be an electrical heater. Other applicable kinds of heating elements may be an infrared heater or an induction heater.

According to a second aspect the object is at least partly achieved by a system for continuous renal replacement therapy. The system comprises a continuous renal replacement monitor with at least one blood pump for continuous pumping of blood, at least one treatment fluid pump for continuous pumping of treatment fluid, and optionally an effluent pump for

continuous pumping of effluent fluid. The system further comprises a blood line associated with the monitor for

extracorporeally circulating blood by means of the blood pump, a fluid distribution circuitry associated with the monitor comprising at least one treatment fluid line for passing treatment fluid by means of the treatment fluid pump and an effluent fluid line for passing effluent fluid, and a blood treatment unit arranged between the blood line and the fluid distribution circuitry. The fluid distribution circuitry further comprises the warming arrangement according to any of the embodiments described herein. According to one embodiment, the effluent fluid line of the system has a portion that is designed to mate with the heating element in order to increase the heat exchange between the heating element and the effluent fluid, wherein the portion is located upstream the heat exchanger.

According to a third aspect, the object is at least partly achieved with a disposable kit. The disposable kit comprises a support structure, a blood line and a fluid distribution circuitry. The fluid distribution circuitry comprises an effluent fluid line and at least one treatment fluid line where all the lines are associated to the support structure and the at least one treatment fluid line has a U-shaped portion designed to cooperate with a respective pump. The fluid distribution circuitry further comprises a heat

exchanger that is configured to be fluidly coupled to the effluent fluid line, and disposed in thermal relationship with the treatment fluid line so as to provide for transfer of heat from the continuously pumped effluent fluid to the

continuously pumped treatment fluid during therapy, and/or disposed in thermal relationship with the blood line, so as to provide for transfer of heat from the continuously pumped effluent fluid to the continuously pumped blood. The effluent fluid line further has a portion that is designed to mate with a heating element configured to transfer heat to the effluent fluid in the effluent fluid line, wherein the portion is located upstream the heat exchanger.

According to one embodiment, the portion has a flattened, bulging shape in order to increase the heat exchange between the heating element and the effluent fluid. According to another embodiemnt, the portion has a shape of a spiral and is designed to encircle the heating element. According to a still further embodiment, the portion comprises a material

configured to increase the heat exchange between the heating element and the effluent fluid.

According to fourth aspect, the object is at least partly achieved with a method for warming an effluent fluid in an effluent fluid line in a continuous renal replacement therapy system with a warming arrangement as disclosed herein, comprising a control unit configured to control the

temperature of the heating element. The method comprises:

receiving at least one measurement signal indicating a temperature and/or a flow rate of at least one of the effluent fluid, the at least one treatment fluid and the blood in the blood line; determining a control parameter based on the indicated temperature and/or flow rate; and controlling the temperature of, or the power delivered to, the heating element based on the control parameter.

According to one embodiment, the method comprises calculating the control parameter based on a model of the heat exchanger.

According to another embodiment, the method comprises warming the at least one treatment fluid to a desired temperature T_set in an interval between 35° and 45° C, preferably between 37° and 43° C.

According to a fifth aspect, the object is at least partly achieved with a computer program at a system, wherein the computer program comprises computer instructions to cause a control unit to perform the method according to any of the steps or embodiments as disclosed herein.

According to a sixth aspect, the object is at least partly achieved with a computer program product comprising computer instructions stored on a computer readable medium for

performing any of the steps of the method.

A continuous flow of both effluent fluid and fresh treatment fluid or fluids and/or blood through the heat exchanger is provided by the disclosure. The heat exchanger may be arranged to work in counter current mode, that is, the heat exchanger is arranged such that the flow of effluent fluid is flowing in the opposite direction to at least one of the flows of treatment fluid or blood during heat exchange. The heating element is further arranged to warm the effluent fluid continuously, which is more efficient than prior art solutions. Further, as the fluid flows are continuous the temperature control may become more accurate. Brief description of the drawings

The present invention is now to be explained in more detail by means of the embodiments below, and with reference to the attached drawings of which: Fig. 1 schematically illustrates a CRRT flow diagram

comprising a warming arrangement for exchanging heat between an effluent fluid and two or three treatment fluids.

Figs. 2A-2D illustrate different embodiments of the heating element and a mating portion of the effluent fluid line.

Fig. 3 schematically illustrates a CRRT flow diagram

comprising a warming arrangement for exchanging heat between the effluent fluid and blood.

Fig. 4 schematically illustrates an embodiment of a disposable kit for a CRRT monitor comprising a heat exchanger and an effluent fluid line configured to be warmed by a heating element .

Fig. 5 schematically illustrates a kit according to Fig. 4 arranged on the CRRT monitor.

Fig. 6 illustrates a flow diagram of a method according to one embodiment.

Detailed description of the invention

Fig. 1 shows a schematic system for continuous renal

replacement therapy, CRRT. The system comprises a blood circuit or blood line la for extracorporeally circulating blood from a patient P through a first compartment 2a of a blood treatment unit 2 by means of at least one blood pump lb (by way of example only one blood pump is shown) . The arrangement further comprises an effluent fluid line 3a for transferring effluent fluid from a second compartment 2b of the blood treatment unit 2 to an effluent fluid container 4 by means of an effluent fluid pump 3b. The first compartment 2a and the second compartment 2b are separated by a semipermeable membrane 2c e.g. of hollow fibre typ. The arrangement

comprises one or more treatment fluid lines such as lines for passing fresh dialysis fluid and/or replacement fluid and/or anticoagulation fluid. The CRRT therapy is monitored and controlled by means of a CRRT monitor (not shown) . The monitor may be microprocessor-based. The monitor may contain all logic and receive and process commands by controlling valves (not shown) and pumps, interpret sensors (not shown) , activate alarms and direct the operation of all aspects of the therapy system.

CRRT may be carried out in three different modes depending on the principle for solute removal: hemodialysis (HD) mode, hemofiltration (HF) mode and hemodiafiltration (HDF) mode. In all modes the CRRT is continuous. This means that blood is pumped continuously during treatment without any intentional interruptions. Thereby the treatment becomes more efficient and its duration my be shortened. The continuous treatment also includes one or several continuously pumped treatment fluids and a continuously pumped flow of effluent fluid during therapy without any intentional interruptions. Thereby a continuous transfer of heat from the effluent fluid to the at least one treatment fluid during therapy and/or a continuous transfer of heat from the effluent fluid to the blood may be achieved during therapy. The continuous treatment however does not exclude that the treatment is stopped e.g. for periods of alarm situations or for exchange of bags with fluid solution. In HD mode, where the solute removal in the blood treatment unit 2 is based on diffusion, fresh dialysis fluid is

transferred from a dialysis fluid source 5 via a dialysis fluid line 6a by means of a dialysis fluid pump 6b to the second compartment 2b of the blood treatment unit 2. The dialysis fluid used in the blood treatment unit 2 is

transferred to the effluent container 4 via the effluent fluid line 3a by means of the effluent pump 3b. In HF mode, where the solute removal in the blood treatment unit 2 is based on convection, the filtrate, i.e. the liquid that has been filtered from the patients blood through the semipermeable membrane, is transferred from the second

compartment 2b of the blood treatment unit 2 to the effluent container 4 via the effluent fluid line 3a by means of the effluent pump 3b. In order to replace some of the filtrate and regain a normal body fluid status of the patient, a

replacement fluid from a replacement fluid source 7 is infused into the blood line la at an infusion point lc arranged upstream the blood treatment unit 2. The replacement fluid is transferred to the infusion point lc in the blood line la via a replacement fluid line 8a by means of a replacement fluid pump 8b. Alternatively the replacement fluid from the

replacement fluid source 7 is infused at an infusion point Id downstream the blood treatment unit 2. The replacement fluid is then transferred to the infusion point Id via the

replacement fluid lines 8a, 8e by means of the replacement fluid pump 8b. The volume of replacement fluid is controlled by means of the CRRT monitor such that it is less than the volume of filtrate. In an alternative CRRT configuration the replacement fluid is constituted by dialysis fluid in the dialysis fluid source 5 and transferred to the infusion point Id in the blood line la via the dialysis fluid lines 6a, 6e by means of the dialysis fluid pump 6b.

In HDF mode, where the solute removal is based on diffusion and convection, both fresh dialysis fluid and replacement fluid is made use of according to the principles described above in connection with HD and HF mode.

In all three modes optionally an anticoagulant fluid from an anticoagulation fluid source 9 is infused into the blood line la at an infusion point le arranged upstream the blood pump lb. The anticoagulant fluid is passed to the infusion point le via an anticoagulation line 10a by means of an anticoagulation fluid pump 10b.

The respective sources for dialysis fluid 5, replacement fluid 7 and anticoagulant fluid 9 may all be in the form of

containers with sterilized and ready for use fluids that are prepared in advance. The fluids 5, 7, 9 are all referred to as treatment fluids to be used for treatment in the CRRT system. Each container may contain a volume of treatment fluid in the range of 1-10 litres. The container may be flexible, rigid or semi rigid. The treatment fluids in the containers may all be cold fluids relatively to the effluent fluid. As will be explained in the following, the temperature difference is used to warm the colder treatment fluids. Thus, the warmer effluent fluid is used to warm one or more of the colder fluids, e.g. the dialysis fluid, replacement fluid, anticoagulant fluid and/or blood. The warming takes place in a heat exchanger 12 arranged in thermal relationship with the effluent fluid so as to provide for transfer of heat from the effluent fluid to the colder treatment fluid or fluids, or blood, to be warmed. A warming arrangement 11 for the CRRT system is illustrated in Fig. 1. The warming arrangement 11 comprises the heat

exchanger 12, that is configured to be fluidly coupled to the effluent fluid line 3a and disposed in thermal relationship with the at least one treatment fluid line 6a, 8a, 10a. The warming arrangement 11 further comprises a heating element 13 configured to transfer heat to the effluent fluid, wherein the heating element 13 is located downstream the blood treatment unit 2 and upstream the heat exchanger 12. The heating element 13 may be located upstream or downstream the effluent pump 3b, if present .

According to one embodiment, the warming arrangement 11 comprises a control unit 14 configured to control the

temperature of the heating element 13 e.g. based on a control parameter. The control unit 14 may be part of the CRRT monitor of the system. The heating element 13 is configured to be connected to the control unit 14 for power supply and/or data transfer. According to one embodiment, the control unit 14 comprises a computer readable memory 31 and a processor or processing unit 32 configured to execute computer instructions stored on the control unit 14. The heating element 13 may provide a continuous warming of the effluent fluid. The heating element 13 is controlled in an appropriate way by the control unit 14 in order to cause a continuous warming of the effluent fluid. This appropriate control of the heating element 13 may include standard on-off control, where the heat transfer from the heating element 13 may fluctuate slightly. Other kinds of appropriate control may include proportional control (P) and/or integral control and derivative control (PID) . The heat exchanger 12 is suitable for continuously warming at least one fluid by means of the effluent fluid, and may be configured to warm two, three, four or more fluids. In Fig. 1 the heat exchanger 12 is illustrated when heating two fluids, i.e. fresh dialysis fluid in a dialysis fluid line 6b, and replacement fluid in a replacement fluid line 8a. Optionally, the heat exchanger 12 may heat a third fluid, a replacement fluid in an anticoagulation fluid line 10a, as illustrated by the dotted line of the anticoagulation fluid line 10a. The heat exchanger 12 may be of plate type or hollow fiber type where the hollow fibers may be of semi-permeable or non- permeable type. One example of a suitable heat exchanger is disclosed in WO2010/040819A1. The heat exchanger 12 may operate in a counter current mode. Counter current mode means that the warmed effluent fluid is arranged to flow in an opposite direction to at least one of the fluids that it exchanges heat with in the heat exchanger 12 during heat exchange . The heating element 13 has according to one embodiment a design to provide for an efficient heat transfer between the heating element 13 and the effluent fluid line 3a. In Figs. 2A-2D a plurality of different embodiments of the heating element 13 with a mating portion 20 of the effluent fluid line 3a are illustrated. The heating element 13 may e.g. be an electrical heater, an infrared heater, an induction heater or another kind of heat source. The effluent fluid line 3a may be provided with a portion 20 upstream the heat exchanger 12 that is designed to provide efficient heat transfer between the heating element 13 and the effluent fluid. The portion 20 may be designed to mate with the heating element 13, and/or be made of a material configured to increase the heat exchange between the heating element 13 and the effluent fluid. In Fig. 2A, an embodiment is shown where the heating element 13 comprises two heating plates 23a, 23b. Fig. 2A illustrates an expanded view of the heating element 13 and portion 20. In operation, the heating element 13 is placed in tight

connection with the mating portion 20, such that the mating portion 20 is placed between the two heating plates 23a, 23b of the heating element 13. At least one side 25 of the heating plates 23a, 23b is intended to face the mating portion 20 for transfer of heat, and may have a rectangular flattened shape as illustrated in the Fig. 2A. The mating portion 20 here has a shape of a bag, e.g. a flattened, bulging shape, with an upper and a lower opposite flattened side 26a, 26b. The mating portion 20 here has a cross-section that is greater than the cross-section of the remaining effluent fluid line 3a. Each heating plate 23a, 23b is located such that the side 25 of the heating plate 23a, 23b intended to face the mating portion 20, faces the upper or lower flattened side 26 of the mating portion 20. If only one heating plate 23a, 23b, then the heating plate 23a, 23b is located to face the upper or lower flattened side 26a, 26b of the mating portion 20. The portion 20 may also have inner channels 24 in the portion 20 for transport of the effluent fluid. The effluent fluid is then forced to flow a longer way than if the effluent fluid had flowed straight through the portion 20, and the heat transfer between the heating element 13 and the effluent fluid in the portion 20 may be increased. The direction of the flow of the effluent fluid through the channels 24 is indicated with hatched arrows. The mating portion 20 may instead comprise only one large channel with a flattened bulging shape (not shown) . Inside the large channel, the effluent fluid is spread out when flowing through the portion 20 in order to increase the heat transfer between the effluent fluid and the side or sides 25 of the heating element or elements 23a, 23b. The control unit 14 is shown connected to the heating element 13, i.e. the heating plates 23a, 23b.

According to another example shown in Fig. 2B, the heating element 13 comprises at least one infraread heater 27a, 27b. The shape of the portion 20 may be the same as any of the embodiments described with reference to Fig. 2A. The infrared heater or heaters 27a, 27b are configured to face the upper and/or lower opposite flattened sides 26a, 26b of the mating portion 20. The control unit 14 is shown connected to the heating element 13, i.e. infrared heaters 27a, 27b.

In another embodiment shown in Fig. 2C, the mating portion 20 has a shape of a spiral and is designed to encircle the heating element 13. The heating element 13 may then have a shape of a rod, e.g. with a corresponding mating recess 28 or trace for the spiral-shaped mating portion 20. The spiral- shaped mating portion 20 may partly or completely be

accomodated or integrated in the rod. According to one

embodiment, the spiral-shaped mating portion 20 is accomodated in the rod such that half the circumference of the spiral- shaped mating portion 20 is in contact with a surface of the recess 28 or trace of the rod. The direction of the flow of the effluent fluid through the mating portion 20 is indicated by the arrows. The control unit 14 is shown connected to the heating element 13, i.e. the rod.

In a further embodiment illustrated in Fig. 2D, the heating element 13 has the shape of an outer casing 29 configured to enclose the mating portion 20. The outer casing 29 may have an opening 34 such that the outer casing can be dressed over the mating portion 20. The outer casing 29 comprises a heating conductor, e.g. a heating thread 30. The heating thread 30 is arranged to the outer casing 29 such that the effluent fluid in the mating portion 20 can be efficiently warmed from the heat of the heating thread 30. The heating thread 30 may be arranged in a regular or unregular pattern to the outer casing 29. According to one embodiment, the heating thread 30 is at least partly arranged inbetween linings of the outer casing 29. According to another embodiment, the heating thread 30 is at least partly arranged on a surface of the outer casing 29, e.g. on the surface facing the mating portion 20 when dressed over the mating portion 20. The heating thread 30 may be arranged to have an extension going back and forth from one side of the outer casing 29 to an opposite side of the outer casing 29 in order to efficiently and uniformly provide heat to the mating portion. The direction of the flow of the effluent fluid through the mating portion 20 is indicated by the arrows. The control unit 14 is shown connected to the heating element 13, i.e. the outer casing 29 and the heating thread 30. Many other alternatives of heating elements 13 and mating portions 20 may however be considered to provide for an efficient heat transfer.

Fig. 3 shows a schematic view of a CRRT system, initially described in connection with Fig. 1, comprising a warming arrangement 11 suitable for warming blood by means of the effluent fluid extracted from the blood treatment unit 2. The heat exchanger 12 is configured to be fluidly coupled to the effluent fluid line 3a and disposed in thermal relationship with the blood line la so as to provide for continuous transfer of heat from the effluent fluid to the blood. Thus, the blood may indirectly be warmed continuously in a safe way via the effluent fluid.

The heating element 13 may have a constant temperature between 40° to 55° C, preferably between 45° to 50° C to warm the effluent fluid before the effluent fluid enters the heat exchanger 12, in order to warm the blood and/or one or more of the treatment fluids. The heating element 13 may then be simultaneously activated when the CRRT system is activated, e.g. by being power supplied by the CRRT system.

The control parameter is according to one embodiment a

parameter which makes the heating element 13 generate an effect needed to warm the at least one of the fluids to a desired temperature T_set and/or blood to a desired temperature T_SetB- The parameter may thus be a power value Qh , current value I , voltage value ¾, duty cycle value or any other

representation of a control parameter used to make the heating element generate the needed effect. The control unit 14 is then configured to control transfer of the power Q_h, current I h , voltage ¾, etc to the heating element 13, or control the heating element 13 according to the duty cycle value etc.

Alternatively, the control parameter is a temperature value T_he of the heating element 13 needed to warm the at least one of the treatment fluids to a desired temperature T_set and/or blood to a desired temperature T_setB- The control unit 14 is then configured to control the temperature of the heating element 13 to the temperature T_he · This may be done by e.g.

transferring a certain power to the heating element 13, or controlling the temperature of the heating element 13 to the temperature T_he ·

The desired temperature T_set of the one or several treatment fluids, or desired temperature T_setB of the blood, may be set from a user interface of the CRRT system. Alternatively, the temperature T_set or temperature T_setB is a predefined value and known to the control unit. Typically, the temperature T_set is in an interval between 35° and 45° C, preferably between 37° and 43° C. The temperature T_setB should be set to a temperature close to a normal body temperature, and is typically set to around 37° C.

In order to determine a suitable control parameter, such as a power value Q_h or temperature value T_hei based on the desired temperature of the one or several treatment fluids or blood, the control unit 14 is configured to receive at least one measurement signal indicating a temperature and/or flow rate of at least one of the effluent fluid, the at least one treatment fluid and the blood in the blood line la. The control unit 14 is then configured to determine the control parameter based on the temperature and/or flow rate.

For example, if the CRRT system is provided with a temperature sensor on the blood line la, i.e. in a return path of the blood line la to the patient P or other destination, e.g. a blood bag, the measured temperature of the blood may be transmitted to the control unit 14 as a measurement signal indicating the measured blood temperature. The measurement signal may be transferred to the control unit 14 via a wire 33, via wireless transmission or exchanged via an internal data network. The control unit 14 is then configured to determine a control parameter based on the measured

temperature of the blood, such that a desired temperature T_setB of the blood may be achieved, and regulate the heating element 13 accordingly. The control parameter may here be determined by using ordinary control algorithms known to the skilled person, such as feedback control. Feedback control here works to minimize the error between the desired temperature T_setB and the measured blood temperature.

According to another embodiment, and in absence of a

temperature sensor on the blood line la, the temperature is measured somewhere in or on the dialysis fluid path. The temperature of the effluent fluid may be measured downstream the heating element 13 but upstream the heat exchanger 12. The temperature of the effluent fluid is then measured after the effluent fluid leaves the heating element 13 but before it enters the heat exchanger 12. In other words, the temperature of the effluent fluid is measured downstream the heating element 13, but upstream the heat exchanger 12. Also the temperature of one or several of the treatment fluids may be measured. The CRRT system is then provided with one or several appropriate temperature sensors. The control unit 14 is then configured to determine a control parameter based on the measured temperature, such that a desired temperature T_set of the one or several treatment fluids may be achieved, and regulate the heating element 13 accordingly. Again, the control parameter may be determined by using ordinary control algorithms known to the skilled person, such as feedback control. Feedback control here works to minimize the error between the desired temperature T_set and the measured

temperature or temperatures of the treatment fluid or fluids.

As previously mentioned, the control parameter may be

determined as an amount of power Q_h , current value I _h , voltage value U_h etc. that has to be transmitted to the heating element 13 to reach a certain temperature T_set of the heating element 13 or of any fluid. This is advantageous if no temperature sensor is present to measure the temperature of the blood or any other fluid.

In the following examples, the control parameter is for simplicity calculated as a desired power value Q_h , but may be converted to a desired voltage U_h, current I_h etc. to the heating element 13. The efficiency of the heating element 13 is usually close to 100%, but may for greater accuracy be measured (e.g. in advance), and the measured efficiency ¾ may be included in the calculations below. Only a fraction η_χ of the heat transferred to the effluent fluid will be transmitted to the treatment fluids in the heat exchanger 14. This

fraction η_χ will depend on the flow rates of the fluids, and may be determined in advance as a model of the heat exchanger 12 for different flow rates. To measure the flow rate of the fluids the system may be provided with appropriate flow rate sensors. The flow rate may also be calculated by using e.g. a rotational speed of the pumps and their known stroke volume. Thus, the control unit 14 may be configured to calculate the control parameter based on a model of the heat exchanger 12.

Both the blood and the treatment fluids will lose some heat Q_a to ambient air. This loss will also depend on the flow rates, which may be used to estimate the loss. The calculation may be done separately for each treatment fluid and for the blood using their individual flow rates, and the results summed to give Q_a. Q_a thus depict the total amount of heat lost to the ambient air.

The treatment fluids should be warmed to a desired temperature T_Set from their initial temperature T₀, e.g. the temperature of the treatment fluids in their bags. The heat required is then Q_f=F-C_P-(T_set-T₀) (1) where F is the flow rate and C_p is the heat capacity of the treatment fluid. Usually C_p, T_set and T₀ are assumed to be equal for the different treatment fluids, and the calculation may then be done with F as the sum of the flow rates for the treatment fluids. Otherwise the equation for Q_f is used on each treatment fluid separately and the results are then summed to give a total Q_f . Even in the absence of the heating element 13, some of the needed heat for warming will be provided by the heat exchanger 12. This heat Q_x may be calculated from the temperature

decrease that the effluent fluid will experience, which is a fraction η_χ (the heat exchanger efficiency) of the totally available temperature difference (T_e-T₀) , where T_e is the temperature of the effluent fluid as it reaches the heat exchanger 12. Q_x will then be:

The amount of power Q_h that needs to be provided to the heating element 13 may now be calculated, taking into account the efficiencies and the losses, according to:

Treatment fluids are used in room temperature, and are

normally stored at lower temperatures. They will during use be warmed by the surrounding air. Assuming that T₀ equals a room temperature of 25°C will therefore overestimate the true temperature and will then prevent overheating of the fluids by overestimating Q_f . The effluent fluid is filtered from the blood, and will experience some temperature loss, but T_e may be assumed to be close to 36°C. Since the losses have already been included in the calculations T_set is not set higher than wanted, e.g. 37°C.

An alternative way of calculating the amount of power Q_h is to replace the estimated heat loss (i.e. setting Q_a=0) by a higher T_set, e.g. 40-43°C.

Another way to calculate the required power Q_h is to determine which temperature T_hi_gh the effluent fluid should have upstream the heat exchanger 12 in order to transfer the required power in the heat exchanger 12. The heat Q transferred by the heat exchanger 12 will then be

Q = F_e-C_p- _x-(T_high-T₀) (4) and this heat Q should heat the fluid (s) and also cover the losses such that:

F_e-C_p- _x-(T_high-T₀) = Q_f+Q_ia (5)

Taking the efficiency of the heating element 13 into account, the power Q_h required to heating element 13 may then be

determined by the required temperature increase from T_e to T_hi_gh as :

Q_h ' _h ~ F_e C_p ^■ (T_high T_e ) (6)

When the heating arrangement is used to warm blood directly, a model or a table may be used by the control unit 14 in order to control the heating element 13 to warm the blood to a desired temperature. For example, the temperature of the effluent fluid may be measured as explained above downstream the heating element 13, but upstream the heat exchanger 12. This temperature of the warmed effluent may be used as a control parameter. If the flow of the effluent is known, e.g. measured by a flow meter or known from the effluent pump rate, and from knowledge about which power that is needed to the heating element 13 to reach a certain temperature of the effluent fluid, the temperature of the effluent fluid upstream the heating element 13 may be calculated. By knowing the blood flow rate and fluid flow rates, e.g. from the rate of the pumps pumping the different fluids, knowing which type of blood treatment device that is used for the treatment, and using the data calculated and measured above, the

effectiveness of the heat transfer in the blood treatment device may be derived from a table or calculation model, and therefrom the energy loss from the blood. When the energy loss from the blood is known, it may be calculated to which desired temperature the effluent fluid should be controlled in order for the blood to reach or regain a desired temperature. In Fig. 4 is shown a principal sketch of a disposable kit in the form of an integrated fluid treatment module comprising a blood line la, and a fluid distribution circuitry comprising an effluent fluid line 3a, multiple treatment fluid lines 6a, 8a, 10a and a heat exchanger 12 that is fluidly coupled to the effluent fluid line 3a and disposed in thermal relationship with the treatment fluid lines 6a, 8a, 10a so as to provide for transfer of heat from the effluent fluid to the treatment fluid. Alternatively or in combination, the heat exchanger 12 may be disposed in thermal relationship with the blood line la, so as to provide for transfer of heat from the effluent fluid to the blood. The lines all have at least a portion forming a U-shaped line length 15, 16, 17, 18, 19 to cooperate with the respective pump, i.e. with the blood pump lb, the effluent fluid pump 3b, the dialysis fluid pump 6b, the replacement fluid pump 8b and the anticoagulation fluid pump 10b. Optionally the disposable kit also comprises a blood treatment unit 2 associated with the blood line la and the fluid distribution circuitry. The lines la, 3a, 6a, 8a, 10a, the blood treatment unit 2 and the heat exchanger 12 are arranged on a support structure 22 indicated with dashed lines for facilitated connection of the lines to the pumps la, 3b, 6b, 8b, 10b. The effluent fluid line 3a further comprises the portion 20 that is designed to mate with a heating element 13 configured to transfer heat to the effluent fluid in the effluent fluid line 3a. The heating element 13 may be one of the herein disclosed embodiments. The portion 20 is located upstream the heat exchanger 12, and downstream the blood treatment unit 2. In the Fig. 4, the portion 20 is located outside the support structure 22, but may instead be arranged on the support structure 22.

The portion 20 may be formed to facilitate the heat exchange between the heating element 13 and the effluent fluid flowing in the portion 20. A plurality of different embodiments of the portion 20 have been explained in connection with the Figs. 2A-2D. A wall segment of the mating portion 20 may also be made thinner than other wall segments of the effluent fluid line 3a, in order to increase the heat transfer. According to one embodiment, the portion 20 comprises a material configured to increase the heat exchange between the heating element 13 and the effluent fluid. The material may be a metal, e.g.

copper. The remaining effluent fluid line 3a may e.g. be made of a plastic material.

The disposable kit is designed to be used together with a CRRT monitor 21 of the type shown in Figure 4. The disposable kit is in use arranged on a front side of the monitor 21. The disposable kit has a blood line la, an effluent fluid line 3a and a multiple of treatment fluid lines 6a, 8a, 10a. All the lines are associated to the support structure 22 and each line has a U-shaped portion 15, 16, 17, 18, 19 (Fig. 4) designed to cooperate with a respective pump 3b, 6b, 8b, 10b (Fig. 4). A blood treatment unit 2 is also arranged on the support

structure 22 and connected to the blood line la and to the dialysis fluid line 6a. Further the heat exchanger 12 is connected to the support structure 22 and fluidly coupled to the effluent fluid line 3a and disposed in thermal

relationship with the treatment fluid line 6a, 8a, 10a so as to provide for transfer of heat from the effluent fluid to the treatment fluid.

Thus in use together with a CRRT monitor, the heat exchanger 12 will be vertically arranged. Vertical arrangement of the heat exchanger 12 will facilitate air bubble dissipation.

However, also arrangement in any other chosen position is feasible. In Fig. 5 is further indicated bags for containing effluent fluid 4, dialysis fluid 5, replacement fluid 7 and anticoagulant fluid 9.

The disclosure also relates to a system for CRRT. The system comprises the continuous renal replacement monitor 21 (Fig. 5) with any of the previously presented at least one blood pump lb, at least one treatment fluid pump 6b, 8b, 10b, and

optionally the effluent pump 3b as illustrated in Figs. 1 and 3. The system further comprises the blood line la associated with the monitor 21 for extracorporeally circulating blood by means of the blood pump lb, and a fluid distribution circuitry associated with the monitor 21 comprising the at least one treatment fluid line 6a, 8a, 10a for passing treatment fluid by means of the treatment fluid pump 6b, 8b, 10b and the effluent fluid line 3a for passing effluent fluid. The system also includes the blood treatment unit 2 arranged between the blood line la and the fluid distribution circuitry. The fluid distribution circuitry comprises a warming arrangement 11 according to any of the embodiments as has been previously described. The effluent fluid line 3a may comprise a portion 20 (Fig. 4) according to any of the embodiments as described herein.

The computer instructions stored on the control unit 14 may be in the form of a computer program P_c. The computer instructions are according to one embodiment configured to cause the control unit 14 to perform a method for warming the effluent fluid in the effluent fluid line 3a in the CRRT system, with the warming arrangement 11 comprising the control unit 14 configured to control the temperature of the heating element 13, according to any of the described embodiments. The method will now be described with reference to the flow chart in Fig. 6. The method comprises receiving at least one measurement signal indicating a temperature and/or a flow rate of at least one of the effluent fluid, the at least one treatment fluid and the blood in the blood line la (Al) . Thereafter the control parameter is determined based on the indicated

temperature and/or flow rate (A2). Based on the control parameter the temperature of, or the power delivered to, the heating element 13 is controlled. The control parameter has previously been described, and the various alternatives of different kinds of control parameters and calculations of the same are here referred to and may be determined and/or

calculated by the method. The disclosure also relates to a computer program product comprising computer instructions stored on a computer readable medium for performing the method as previously described.

The invention is not restricted to the herein described embodiments and the figures, and may be varied freely within the claims. For example may any of the embodiments where a temperature of the blood and/or any of the fluids is measured be combined with any of the embodiments where temperature measurements are not needed to, if possible, achieve a further verified control parameter.

Claims

A warming arrangement (11) for a continuous renal replacement therapy system, wherein the system comprises a blood treatment unit (2) connecting a blood line (la) for extracorporeally circulating blood and a fluid distribution circuitry comprising at least one treatment fluid line (6a, 8a, 10a) for passing treatment fluid, and an effluent fluid line (3a) for passing effluent fluid, wherein the warming arrangement (11) comprises a heat exchanger (12) configured to be fluidly coupled to the effluent fluid line (3a) and disposed in thermal

relationship with the at least one treatment fluid line (6a, 8a, 10a) so as to provide for transfer of heat from the continuously pumped effluent fluid to the at least one continuously pumped treatment fluid during therapy, and/or disposed in thermal relationship with the blood line (la) so as to provide for transfer of heat from the continuously pumped effluent fluid to the continuously pumped blood during therapy, characterized in that the warming arrangement (11) comprises a heating element (13) configured to transfer heat to the effluent fluid, wherein the heating element (13) is located downstream the blood treatment unit (2) and upstream the heat exchanger ( 12 ) .

The warming arrangement (11) according to claim 1, comprising a control unit (14) configured to control the temperature of the heating element (13) based on a control parameter.

The warming arrangement (11) according to claim 2, wherein the control unit (14) is configured to receive at least one measurement signal indicating a temperature and/or flow rate of at least one of the effluent fluid, the at least one treatment fluid and the blood in the blood line (la), and to determine the control parameter based on the temperature and/or flow rate.

The warming arrangement (11) according to claim 2 or 3, wherein the control parameter is either of a parameter which makes the heating element (13) generate an effect, or a temperature value T_he of the heating element (13), needed to warm the at least one of the treatment fluids to a desired temperature T_set and/or blood to a desired temperature T_setB.

The warming arrangement (11) according to claim 4, wherein the control unit (14) is configured to calculate the control parameter based on a model of the heat exchanger ( 12 ) .

The warming arrangement (11) according to claim 4 or 5, configured to warm the at least one treatment fluid to a desired temperature T_set in an interval between 35° and 45° C, preferably between 37° and 43° C.

The warming arrangement (11) according to any of the preceding claims, wherein the heating element (13) comprises at least one heating plate configured to warm the effluent fluid in the effluent fluid line (3a) .

A system for continuous renal replacement therapy

comprising

- a continuous renal replacement monitor (21) with at least one blood pump (lb) for continuous pumping of blood, at least one treatment fluid pump (6b, 8b, 10b) for continuous pumping of treatment fluid, and optionally an effluent pump (3b) for continuous pumping of effluent fluid;

- a blood line (la) associated with the monitor (21) for extracorporeally circulating blood by means of the blood pump (lb);

- a fluid distribution circuitry associated with the monitor (21) comprising at least one treatment fluid line (6a, 8a, 10a) for passing treatment fluid by means of the treatment fluid pump (6b, 8b, 10b) and an effluent fluid line (3a) for passing effluent fluid, and

- a blood treatment unit (2) arranged between the blood line (la) and the fluid distribution circuitry characterized in that the fluid distribution circuitry comprises a warming arrangement (11) according to any of claims 1 to 7.

The system according to claim 8, wherein the effluent fluid line (3a) has a portion (20) that is designed to mate with the heating element (13) in order to increase the heat exchange between the heating element (13) and the effluent fluid, wherein the portion (20) is located upstream the heat exchanger (12) .

The system according to claim 9, wherein the portion (20) comprises a material configured to increase the heat exchange between the heating element (13) and the

effluent fluid.

A disposable kit comprising

a support structure (22);

a blood line (la);

a fluid distribution circuitry comprising an

effluent fluid line (3a) and at least one treatment fluid line (6a, 8a, 10a) where all the lines are associated to the support structure (22) and the at least one treatment fluid line having a U-shaped portion (15, 16, 17, 18, 19) designed to cooperate with a respective pump (6b, 8b, 10b) , the fluid distribution circuitry further comprises a heat exchanger (12) that is configured to be fluidly coupled to the effluent fluid line (3a) , and disposed in thermal relationship with the treatment fluid line (6a, 8a, 10a) so as to provide for transfer of heat from the continuously pumped effluent fluid to the continuously pumped treatment fluid during therapy, and/or disposed in thermal relationship with the blood line (la), so as to provide for transfer of heat from the continuously pumped effluent fluid to the continuously pumped blood during therapy, characterized in that the effluent fluid line (3a) has a portion (20) that is designed to mate with a heating element (13) configured to transfer heat to the effluent fluid in the effluent fluid line (3a) , wherein the portion (20) is located upstream the heat exchanger (12) .

12. Disposable kit according to claim 11, wherein the portion (20) has a flattened, bulging shape in order to increase the heat exchange between the heating element (12) and the effluent fluid.

13. Disposable kit according to claim 11, wherein the portion (20) has a shape of a spiral and is designed to encircle the heating element (12) .

14. Disposable kit according to any of claims 11 to 13, wherein the portion (20) comprises a material configured to increase the heat exchange between the heating element (13) and the effluent fluid.

15. A method for warming an effluent fluid in an effluent fluid line (3a) in a continuous renal replacement therapy system with a warming arrangement (11) according to any of claims 1 to 7 comprising a control unit (14)

configured to control the temperature of the heating element (13), the method comprising

receiving at least one measurement signal indicating a temperature and/or a flow rate of at least one of the effluent fluid, the at least one treatment fluid and the blood in the blood line (la);

determining a control parameter based on the indicated temperature and/or flow rate; controlling the temperature of, or the power

delivered to, the heating element (13) based on the control parameter.

16. Method according to claim 15, wherein the control parameter is either of a parameter which makes the heating element (13) generate an effect, or a temperature value The of the heating element, needed to warm the at least one of the treatment fluids to a desired

temperature T_set and/or blood to a desired temperature T_SetB ·

17. The method according to claim 16, comprising

calculating the control parameter based on a model of the heat exchanger.

18. The method according to any of claims 15 to 17,

comprising warming the at least one treatment fluid to a desired temperature T_set in an interval between 35° and 45° C, preferably between 37° and 43° C.

19. A computer program at a system, wherein the computer program comprises computer instructions to cause a control unit (14) to perform the method according to any of the claims 15 to 18.

20. A computer program product comprising computer

instructions stored on a computer readable medium for performing the method according to any of the claims 15 to 18.