EP1539287A2

EP1539287A2 - An apparatus for supplying a patient a mixture of a carrier gas and a gaseous anaesthetic agent

Info

Publication number: EP1539287A2
Application number: EP03757776A
Authority: EP
Inventors: Robert Axelsson; Olof Franksson; Oliver Trepte; Caroline Lundin
Original assignee: Anmedic AB
Current assignee: Anmedic AB
Priority date: 2002-09-11
Filing date: 2003-09-02
Publication date: 2005-06-15
Also published as: WO2004024222A3; AU2003273813A8; WO2004024222A2; AU2003273813A1; SE0202721L; SE0202721D0; SE526014C2

Abstract

An apparatus (1) for supplying a patient with a mixture of a carrier gas and a gaseous anaesthetic agent, said apparatus comprising a producing part (2,) for providing the gaseous anaesthetic agent by evaporating a volatile liquid anaesthetic agent, and an operating part (3) for operating the producing part (2). The producing part comprises a liquid container (5), a gas container (6) and a pump (8) for dosing the liquid anaesthetic agent to the gas container (6) inserted in a connection (7) between the two containers. Said components of the producing part are permanently connected to each other during the lifetime of the producing part. This is an advantage e.g. when the producing part (2) is a disposable enclosure (4), since this will ensure that the producing part easily can be replaced with a new producing part restoring the anaesthetic supply in the apparatus quickly and easily without the operator having to spend time on cleaning and sanitising/sterilising the components of the producing part.

Description

An apparatus for supplying a patient a mixture of a carrier gas and a gaseous anaesthetic agent

The present invention relates to an apparatus for supplying a patient with a mixture of a carrier gas and a gaseous anaesthetic agent, said apparatus comprising a producing part for providing the gaseous anaesthetic agent by evaporating a volatile liquid anaesthetic agent. Said producing part comprises a liquid container for the liquid anaesthetic agent, a gas container for the gaseous anaesthetic agent, a connection between the two containers, a pump inserted in this connection which during operation of the apparatus pumps liquid anaesthetic agent from the liquid container to the gas container.

Apparatuses of this type are generally having a combined liquid container and gas container, and are operated by evaporating a desired amount of liquid anaesthetic agent and mixing the vapour with a carrier gas, which is introduced into a breathing circuit for inhalation by a patient.

Such apparatuses are expected to deliver predictable doses of anaesthetic agent over a wide range of conditions. For instance, the flow of carrier gas has to be carefully regulated in order to maintain the correct dosage of anaesthetic vapour since the volume of the vapour receiving portion increases when the liquid evaporates . The lethal dose for inhalation anaesthetics is about 2 to 3 times the therapeutic dose for surgery, meaning that there only is a safety margin of about 3 to 1.

Most known producing parts of such apparatuses are of the bypass type, comprising a container for containing an anaesthetic agent. A carrier gas such as air, oxygen and/or nitrous oxide is divided between a first stream, which is directed through the container to entrain vapour from the liquid anaesthetic, and a second bypass stream. The two streams are subsequently recombined for delivery to a patient.

In another embodiment of such a producing part the evaporated anaesthetic agent is injected directly into the carrier gas flow at a rate, which is determined by the pressure difference between the carrier gas and the anaesthetic vapour.

These known apparatuses have a number of drawbacks . One example is that when a filled vaporiser is carried from one station to another (e.g. from a storage rack to an anaesthesia machine) the liquid container can inadvertently be inverted or tilted to such a degree, even though there may be no gas flowing through it at the time, that the danger exists that it subsequently will deliver a higher than intended anaesthetic agent concentration if the liquid has been permitted to collect in any part of the gas outlet passages.

The apparatus disclosed in WO 9911312 has overcome this problem, as the anaesthetic agent is placed in a separate liquid container. The anaesthetic then enters a gas container, which is in thermal contact with a heating surface to ensure evaporation of anaesthetic droplets on entry into the chamber.

The known anaesthetic containers are arranged in such a way that they can be refilled with an anaesthetic agent from a larger container. In e.g. hospitals such a container is not very accessible to the staff that must check the content of the container and often refill it with new anaesthetic agent under appropriate conditions. Furthermore, refilling the container can easily cause leaks, resulting in anaesthetic contamination of the air.

The most commonly used anaesthetics agents are halothane, desflurane, enflurane, isoflurane and sevoflurane, some of which are inclined to crystallise in the gas container in the producing part of the apparatus resulting in unpredictable dosage to the patient during use of the apparatus if the producing part is not thoroughly cleaned between two operations .

Moreover, when a new anaesthetic agent is applied to the producing part of the apparatus every surface that has been in contact with the carrier gas and the anaesthetic agent must be extensively cleaned and sanitised/sterilised for securing that the anaesthetic agent is not contaminated by e.g. bacteria, or mixed with another anaesthetic agent which could cause a hazard for the patient.

Therefore, attending to these known apparatuses is rather difficult and time-consuming for an often busy staff.

Another problem of these known apparatuses is that their producing part is rather complex and therefore expensive, and that they comprise a large number of components, which are subjected to wear and tear, which inevitably will require regular maintenance.

It is therefore one object of the invention to provide an apparatus of the kind mentioned in the opening paragraph, which in an simple and user-friendly manner can be charged with a new liquid anaesthetic agent, without the need for thorough cleaning and sanitising/sterilising of all surfaces which have been in contact with a previous anaesthetic agent.

Another object of the invention is to provide an apparatus of the kind mentioned in the opening paragraph, which has a simple, inexpensive construction with no components that gradually would become ineffective and unpredictable through wear. A third object of the invention is to provide an apparatus of the kind mentioned in the opening paragraph having a producing part for providing the gaseous anaesthetic agent constructed as a disposable part.

This is achieved according to the invention by the fact that the producing part further comprises means for ensuring that at least a number of said components of the producing part are permanently connected to each other during the lifetime of the producing part.

As the different components of the producing part never are separated from each other, the risk for contamination of the apparatus, which the conventional apparatuses of this type suffer from, is fully eliminated.

An additional advantage of using the described producing part is that, since no liquid anaesthetic agent is in the gas container before use, its internal volume can be kept low so that there is no bolus or lag during start-up.

In a preferred embodiment of the invention the means for ensuring that that said components of the producing part are permanently connected to each other can be an enclosure, e.g. a box or housing, encapsulating said components in such a way that it is not possible to separate the components from each other .

In this manner the parts are safely protected against being dismantled, and the liquid container therefore will always be connected to the respective gas container. This means that the possibility of mixing a previously used anaesthetic agent with another anaesthetic agent in the gas container is eliminated.

As the producing part is never dismantled, the internal surfaces of this will not be contaminated by e.g. bacteria when the liquid container is filled in advance. The apparatus therefore can be used without risk for the patient.

The apparatus according to the invention can be based on the use of disposable enclosures, i.e. enclosures that each time are discarded after being used and then replaced by a new, filled enclosure. These disposable enclosures are each provided with a liquid container. Gas container and pump and will thus not be subject to crystallization of the anaesthetic agent and/or contamination of e.g. bacteria. All parts will therefore always be able to function effectively and hygienically . Furthermore, the disposable enclosure solves the problem with crystalline salts from the anaesthetic agent that are accumulated in the gas container.

Furthermore, the anaesthetic supply in the apparatus can be restored quickly and easily without an operator having to spend time and energy on cleaning and sanitising/sterilising the components of the producing parts.

To ensure that no liquid anaesthetic can enter the gas container before the pump is activated, either before or during use, the producing part can further comprise means for tightly closing the liquid connection between the two containers. The producing part can then be stored, transported and used without risk of overdosing the patient on reason that the gas container unintendedly had been filled with too much liquid agent.

In one embodiment according to the invention, which is simple and cheap and furthermore functions effectively and safely, the pump itself could be said means for tightly closing the liquid connection between the two containers.

The pump could in this embodiment be constructed as an electrically driven piston pump, having at least one piston operating in a valve house between a first position, where the connection between the two containers is open and a second position, where said connection is closed, or the pump could have two pistons arranged in such a way, that the liquid connection between the two containers is kept closed at all times .

Another possibility for tightly closing the connection between the two containers, when the pump is not activated, could be to insert at least one spring loaded valve in the connection between the two containers, and then use a pump which is adapted to generate a pressure difference over the valve high enough to open the valve against the force of the spring acting on the valve. This possibility can be used either with a conventional pump or in combination with the pump described above. In either case the spring-loaded valve is providing an extra security against liquid anaesthetic agent entering the gas container.

The spring loaded valve can optionally be inserted downstream of the pump in the connection between the two containers, whereby the pressure difference over the valve advantageously will be the difference between the outlet pressure of the pump and the pressure in the gas container, resulting in that the pump immediately will start to function as a part of the pump already is filled with the liquid agent.

In ensuring that the liquid anaesthetic agent in the liquid container steadily and safely flows down to the input of the pump when it is activated, the liquid container advantageously can be placed at a higher level than the gas container in the operative state.

In a very simple and cheap embodiment according to the invention the pump of the producing part can also be adapted to dose the liquid agent in accordance with the patient dosage requirements .

In order to operate the producing part, the apparatus can also comprise an operating part. This operating part can e.g. have an electrical motor for driving the pump, an electrical heating and/or cooling element for evaporating the liquid anaesthetic agent, and a control panel for controlling the process of the apparatus. This operating part can also comprise the connections to a gas conduit for the carrier gas and to an electrical supply.

The operating part is preferably arranged so that the gas container of the producing part, when this is in the operative state, will be in thermal contact with the heating element of the operating part. This will ensure efficient evaporation of the particular anaesthetic agent being supplied. For certain anaesthetic agents, and under conditions with high room temperature, the gas container may need to cool the agent rather than heating it. The temperature of the heating element and thereby the gas container can e.g. be controlled by a microcontroller placed in the operating part, and the heating element could be a Peltier element, thereby making it possible to heat or cool using the same element.

The producing part and the operating part can optionally be releasably coupled to each other, when the apparatus is in its operative state. This is an advantage e.g. when the producing part is a disposable enclosure, since this will ensure that the producing part can be replaced with a new producing part restoring the anaesthetic supply in the apparatus quickly and easily without having to spend time and energy on cleaning and sanitising/sterilising the components of the producing part.

In some cases it can be of interest to refill the liquid container with an anaesthetic agent. In such cases the liquid container in the producing part can comprise an opening, through which the anaesthetic agent can be filled or refilled, said opening is closed when the apparatus is in its operative state .

The invention also relates to a pump to the apparatus according to the invention being a piston pump comprising two pistons in a valve house having an inlet and an outlet for the liquid agent placed at an axial distance from each other.

The pistons can be adapted to reciprocate in the valve house between a first position where the two pistons in an abutting state are closing the inlet of the valve house, a second position where the two pistons in a separated state on either side of the inlet of the house, a third position where the two pistons in a separated state are on either side of the outlet of the house, and a fourth position where the two pistons in an abutting state are closing the outlet of the valve house.

When a dosage has to be provided to the gas container the pistons will move to the second position and the gap between the two pistons will be filled with a volume of liquid agent from the liquid container. This volume is transported to the third position and is in the fourth position squeezed out into the outlet of the house. The pistons are in all positions tightly closing the liquid connection between the liquid - and gas container. A spring can be provided for keeping the pistons in one of these positions securing that no liquid anaesthetic agent unintendedly enters the gas container before taking the apparatus in use and activating the pump. In this way the pump is able to accurately dose the liquid agent in accordance with the patient dosage requirements.

The invention further relates to a method for filling the apparatus according to the invention with the liquid anaesthetic agent, said method comprises filling the liquid anaesthetic agent into the liquid container before assembly of the producing part.

Another aspect of the invention is the use of the apparatus according to the invention in an anaesthetic machine. The apparatus is dosing a liquid anaesthetic agent, by evaporation a volatile liquid anaesthetic agent, mixing the vapour with a carrier gas and introducing the mixture into the breathing circuit of an anaesthetic machine for inhalation by a patient.

In still other embodiments the enclosure and liquid container could comprise a lid, which could be used in case the operator wants to refill the liquid container with new anaesthetic agent. This could be an advantage in cases where the same anaesthetic agent is needed for several continued operations.

Another possibility could be to divide the producing part into several parts. One example of this is that the liquid container and the pump could be a first part and the gas container could be a second part. In that case the first enclosure could be in a disposable enclosure and the second part could be a part of the operating part or the anaesthetic machine, or vice versa. In this manner the producing part could be divided in a number of different ways.

The invention will be explained in greater details below, describing only examples of embodiments with reference to the drawing, in which

Fig 1. shows a schematic view of a first embodiment of the apparatus according to the invention in operative state,

Fig 2. is a sectional view taken along the line II - II in fig. 1, Fig 3a. shows a pump according to the invention in a first position,

Fig. 3b shows the same in a second position,

Fig. 3c shows the same in a third position, and

Fig. 3d shows the same in a forth position,

In the following, it is assumed that all components of the producing part are permanently connected to each other.

Fig. 1 shows a schematic view of an apparatus according to the invention generally designated by the reference numeral 1. The apparatus is especially intended for being mounted in an anaesthetic machine for dosing a liquid anaesthetic agent by evaporation of a volatile liquid anaesthetic agent, mixing the vapour with a carrier gas and introducing the mixture into the breathing circuit of an anaesthetic machine for inhalation by a patient.

The main components of the apparatus are a producing part 2 and an operating part 3.

In the following, it is assumed that the producing part 2 is encapsulated in a disposable enclosure 4, which is an enclosure, which is discarded when used and replaced by a new enclosure filled with a fresh portion of volatile liquid anaesthetic agent.

The producing part 2 consists of a liquid container 5 for the liquid anaesthetic agent, a gas container 6 for the gaseous anaesthetic agent placed, in this case, downstream for the liquid container, a connection 7 between the two containers, and a pump 8 inserted in the connection 7 for pumping liquid agent to the gas container during operation. To ensure that no liquid anaesthetic agent can enter the gas container 6 before the pump 8 is activated, either before or during use, a spring loaded valve 9 is inserted downstream of the pump. The disposable enclosure 4 can therefore be stored, transported and used without any risk of overdosing the patient because the gas container 6 unintendedly has been filled with liquid agent.

The operating part 3 can be a releasable part or an integrated part of an anaesthetic machine. The components of the operating part 3 is an electrical motor 10 for driving the pump 8, an electrical heating and/or cooling element 11 for evaporating the liquid anaesthetic agent, a connection to a gas conduit 13 for the carrier gas and a control panel 12 for controlling the process of the apparatus 1. An electrical supply 14 is providing the required electricity to the apparatus .

The operating part may be connected to a gas mixer (not shown) for delivering the required composition of carrier gas such as fresh air, oxygen and/or nitrous oxide to the gas conduit 13, where the carrier gas is mixed with a gaseous anaesthetic agent thereby providing a controlled mixture of carrier gas and anaesthetic vapour to a patient.

In order to ensure that the flow requirements are met can e.g. flow sensors (not shown) be inserted in the gas conduit 13.

Apart from these flow sensors, no additional valves or flow restrictors need to be present in the gas conduit 13, meaning that the flow resistance is relatively low and constant.

Therefore, no bypass flows are necessary.

In the operative state the producing part 2 and the operating part 3 are releasably coupled to each other, via a gas connection 16 and a coupling 17. Fig. 2 shows that the gas conduit 13 extends transversely to the operating part of the apparatus from one side to the other. At the inlet the conduit is connected to a conduit (not shown) for carrier gas and at the outlet to a conduit (not shown) for the controlled gas mixture to the patient.

As the producing part is encapsulated in the disposable enclosure 4, a used enclosure 4 can be replaced with a new producing enclosure, meaning that a given anaesthetic machine readily can be adapted for the administration of any of the available anaesthetic agents and, using the same basic anaesthetic machine, the anaesthetist is accordingly given the freedom to match the correct agent as far as possible to the needs of every patient, without having to thoroughly clean and sanitise/sterilise the components of the producing part, i.e. the components which have been in contact with the anaesthetic agent .

When the apparatus is operating liquid anaesthetic agent is transferred from the liquid container 5 via the connection 7 by means of the pump 8, the pumping rate of which is accurately controlled by a microcontroller 18. The pump may, for example, be capable of delivering from 0,03 μl to 100 μl per second, so that liquid anaesthetic agent thus can be delivered to the gas container 6 at an accurately controlled rate .

The liquid then enters the gas container 6 through an inlet, which e.g. could be in the form of an injection needle (not shown) having a chamfered tip. The needle is of fine gauge to deliver anaesthetic agent in the form of microdroplets . The sharp edge of the tip is in contact with a vaporisation surface 19, which is thermally coupled to the heating element 11 operated by the microcontroller 18. The microcontroller can produce heating or cooling of the surface 19, as required. A sensor (not shown) can detect the anaesthetic agent being supplied, and the temperature of the vaporisation surface 19 is automatically adjusted for the chosen anaesthetic agent.

The tip of the needle is preferably in direct contact with the surface 19. Although there could be a small gap between the needle and the surface 19 direct contact is preferred since a small volume of liquid (e.g. about 0.1 μl) would not fall into contact with the surface 19 under gravity. Thus, when liquid anaesthetic agent enters the gas container 6 the microdroplets come directly into contact with the surface 19 and the anaesthetic agent is immediately vaporised so that the gas container never contains any significant quantity of liquid anaesthetic agent.

The operating part 3 may include battery backup 15 for uninterrupted operation in the event of a power failure. When using the apparatus, the operator is by means of the control panel 12 delivering input to the microcontroller for controlling the apparatus .

Said control panel 12 is also incorporating a display that e.g. presents the percentage of anaesthetic agent being delivered into the carrier gas.

The producing part 2 could further incorporate temperature sensors (not shown), e.g. for monitoring ambient temperature, the temperature of the gas container 6 and the temperature of the carrier gas.

If no evaporation is taking place in the gas container 6 the pressures in the connection 7, gas conduit 13 and gas container will be equalised, but this pressure will be constantly varying due to patient-related factors.

If the operator by means of the control panel 2 sets a desired percentage of anaesthetic agent in the gas mixture to be supplied to the patient, the microcontroller calculates the required rate of anaesthetic agent using a software algorithm which takes account of fresh carrier gas flow, as signalled by the flow sensors, and parameters of the particular anaesthetic agent being supplied, e.g. boiling point etc.

The pump 8 then is ordered to supply the gas container 6 with the required rate of liquid agent from the liquid container, and as soon as evaporation commences the pressure in the gas container 6 will rise above that in gas conduit 13 causing anaesthetic vapour to be injected into the carrier gas in the gas conduit 13.

This pressure rise is determined by natural constants of the anaesthetic, including the K factor for the difference in volumes before and after vaporisation, so that the amount of anaesthetic agent injected is independent of the output pressure. As a result, the percentage of anaesthetic agent in the gas mixture to the patient is considerably more stable and accurately controllable than in conventional apparatuses and is furthermore independent of external factors such as temperature, pressure, humidity etc.

Fig. 3 shows an embodiment of a pump for pumping liquid anaesthetic agent for being evaporated in the gas container.

The pump is designated by the reference numeral 20, and is having a first piston 21' and a second piston 21'' located in a valve house 22 having an inlet 23 communication with the liquid container and an outlet 24 communication with the gas container .

The pistons 21' and 21'' are adapted to reciprocate in the valve house 22. In fig. 3a the two pistons are shown in a first position where they are in abutting state and thereby closing the inlet of the valve house, ensuring that no liquid from the liquid container can enter the valve house.

When a dosage has to be provided to the gas container the second piston 21'' travels to a second position shown in fig. 3b leaving a gap 25 between the two pistons. A distance pipe 26 is regulating said gap, and is controlled by e.g. a microcontroller .

In the second position the gap 25 between the two pistons is filled with a volume of liquid agent from the liquid container. This volume is transported to the third position, shown in fig. 3c.

In the fourth position, shown in fig. 3d, said volume is squeezed out into the outlet 24 of the house 22 whereby it is entering the gas container at e.g. the vaporising surface.

A spring (not shown) can be provided for keeping the pistons 21' and 21'' in one of these positions securing that no liquid anaesthetic agent unintendedly enters the gas container before the user takes the apparatus in use and activates the pump.

Claims

1. An apparatus (1) for supplying a patient a mixture of a carrier gas and a gaseous anaesthetic agent, said apparatus comprises a producing part (2) for providing the gaseous anaesthetic agent by evaporating a volatile liquid anaesthetic agent, said producing part (2) comprises a liquid container (5) for the liquid anaesthetic agent, - a gas container (6) for the gaseous anaesthetic agent, a connection (7) between the two containers, a pump (8) inserted in this connection for pumping liquid anaesthetic agent from the liquid container (5) to the gas container (6) during operating of the apparatus (1), characterised in, that the producing part further comprises means for ensuring that at least a number of said components of the producing part are permanently connected to each other during the lifetime of the producing part .

2. An apparatus according to claim 1, characterised in, that all components of the producing part are permanently connected to each other during the lifetime of the producing part.

3. An apparatus (1) according to claim 1 or 2 , characterised in, that the means for ensuring that said components of the producing part (2) are permanently connected to each other is an enclosure (4) encapsulating said components in such a way that it is not possible to separate the components from each other.

4. An apparatus (1) according to claim 1, 2 or 3, characterised in, that the producing part further comprises means for tightly closing the connection (7) between the two containers (5,6), when the pump (8) is not activated.

5. An apparatus (1) according to claim 4, characterised in, that the means for tightly closing the connection (7) between the two containers (5,6), when the pump (8) is not activated, is said pump constructed as an electrically driven piston pump (20) having at least one piston (21', 21'') operating in a valve house (22) between the two containers (5,6).

6. An apparatus (1) according to claim 4, characterised in, that the means for tightly closing the connection (7) between the two containers, when the pump (8) is not activated, is at least one spring loaded valve (9) inserted in the connection (7) between the two containers

(5,6), and that the pump (8) is adapted to generate a pressure difference over the valve high enough to open the valve against the force of the spring acting on the valve.

7. An apparatus (1) according to claim 6, characterised in, that the at least one spring loaded valve (9) is inserted downstream of the pump (8) in the connection between the two containers (5,6) .

8. An apparatus (1) according to claim 5, characterised in, that the piston pump (20) is adapted to dose the liquid agent in accordance with the requirements of the patient.

9. An apparatus (1) according to claim 1 - 9 and where the apparatus further comprises an operating part (3) for operating the producing part (2), characterised in, that said operating part comprises - an electrical motor (10) for driving the pump (8), an electrical heating and/or cooling element (11) for evaporating the liquid anaesthetic agent, and a control panel (12) for controlling the process of the apparatus (1) .

10. An apparatus (1) according to claim 10, characterised in, that the producing part (2) and the operating part (3) are releasably coupled to each other, when the apparatus (1) is in its operative state.

11. An apparatus (1) according to claim 10 or 11, characterised in, that the operating part (3) comprises connections (16,17) to a gas conduit (13) for the carrier gas and to an electrical supply (14) .

12. An apparatus according to claim 1 - 11, characterised in, that the producing part and/or the operating part are disposable .

13. An apparatus according to claim 1 - 12, characterised in, that the liquid container in the producing part comprises an opening, through which the anaesthetic agent can be filed or refilled, said opening is closed when the apparatus (1) is in its operative state.

14. A pump to the apparatus (1) according to claim 1 - 13, characterised in that the pump (20) is a piston pump comprising two pistons (21 ',21'') in a valve house (22) having an inlet (23) and an outlet (24) for the liquid agent placed at an axial distance from each other, the pistons being adapted to reciprocate in the valve house

(22) between a first position where the two pistons in an abutting state are closing the inlet of the valve house, a second position where the two pistons in a separated state are on either sides of the inlet of the house, a third position where the two pistons in a separated state are on either sides of the outlet of the house, and a fourth position where the two pistons in an abutting state is closing the outlet of the valve house.

15. A method for filling the apparatus (1) according to claim 1 - 13 with a quantity of the liquid anaesthetic agent, characterised in, that the method comprises filling the liquid anaesthetic agent into the liquid container.

16. A use of the apparatus (1) according to claim 1 - 13 for dosing a liquid anaesthetic agent in an anaesthetic machine, by evaporation a volatile liquid anaesthetic agent, mixing the vapour with a carrier gas and introducing the mixture into the breathing circuit of an anaesthetic machine for inhalation by a patient.