WO2001037911A1

WO2001037911A1 - Anaesthesia unit

Info

Publication number: WO2001037911A1
Application number: PCT/SE2000/002281
Authority: WO
Inventors: Ola Stenqvist
Original assignee: A+ Science Invest Ab
Priority date: 1999-11-23
Filing date: 2000-11-21
Publication date: 2001-05-31
Also published as: SE9904244D0; AU1653301A

Abstract

An anaesthesia unit which operates according to the recirculatory system with circulation in a flow duct (1) while passing an absorber (3) of carbon dioxide. The duct has a connection (2) to the patient and when the patient exhales, breathing gas has to be brought to the inlet side (13) of the absorber and when the patient inhales, the gas must be carried away from the outlet side (15) of the absorber, whereas a corresponding direction of flow regarding the circulation of gas in the duct is ensured. In order to maintain this direction of flow, at least one ejector (18) with pumping action is connected to the duct. The ejector has an outlet opening (19), placed in a throttle (20), for gas from a gas pump (23), which pumps gas from a connection (25) to the duct (1) and back into the duct through the outlet opening (19).

Description

ANAESTHESIA UNIT

TECHNICAL FIELD

The present invention relates to an anaesthesia unit which operates according to the so-called recirculatory system.

PRIOR ART

The fact that an anaesthesia unit operates according to the recirculatory system means that the breathing gas flows m a circular path while passing an absorber of carbon dioxide. After passing the absorber, the gas which is exhaled by the patient is brought back to the patient during inhalation. Thus, oxygen and anaesthesia gas which have not been consumed can be recirculated to the patient together with newly added oxygen and anaesthesia gas to replace the consumed part. Simultaneously, adequate conditioning of the inhaled gas is obtained by maintaining the heat and humidity absorbed from the patient.

This means that the unit contains a flow duct for the gas along which the gas has to pass the absorber. The duct has connections to the patient, to a mechanical or manual ventilator for artificial breathing support and for visual control of the breathing and to supply lines for oxygen and anaesthesia gas and possibly other additives. In order to maintain the flow m the duct m the intended direction, i.e. m connection with exhalation, to the absorber inlet and, m connection with inhalation, from the absorber outlet for the gas which is free from carbon dioxide, it is known to arrange one-way valves m the duct. A first such valve is thus adapted to let m the exhalation gas only m the duct part before the absorber and a second valve is adapted to release gas from the duct part after the absorber only during inhalation. Such anaesthesia units operating according to the recirculatory system and provided with one-way valves for the inhalation and exhalation gas are known from, for example US-A-4, 127,121 and US-A-4 , 637 , 386.

These one-way valves, in general two valves, involve some disadvantages. For opening, a certain gas pressure is required, which has to be generated by the patient's breathing, and in connection with the opening and closing procedure a certain degree of return flow in a non- intended direction cannot be avoided. This may affect the patient unfavourably, especially weak patients and, in particular, infants which have a small total lung capacity and a fast breathing rhythm. Another disadvantage relates to the cleaning of the unit, which should be carried out after each use. Thus, the cleaning of the valves requires special measures, which means that they must have a special design, usually in the form of a special component which is dismountable from the rest of the unit and may be cleaned separately. It has also been found that serious operating disturbance may appear after cleaning due to blocked valves . Swedish published patent application No. 454 948

(SE-B-8400839-0, M. Baum) discloses a valveless recirculatory system. In order to maintain the necessary direction of flow with the exhalation air directed to a carbon dioxide absorber and the inhalation air from the same af- ter passage, on the one hand a jet nozzle and, on the other, a gas injector are provided, which are stated to be supplied with breathing gas. The jet nozzle injects breathing gas at high speed intermittently in a controlled process. Thus, despite the absence of valves, an opportunity is created to obtain the desired direction of circulation since, when inhalation is to occur, the jet nozzle makes the gas in the recirculatory system move in the direction away from the absorber by means of injection of gas, which is supported by said injector. Fur- ther ore , the provision of an ejector nozzle is suggested, in which the ejection of gas is also directed, but in the direction opposite to the ejection of the jet nozzle, the ejector nozzle supporting the flow in the recirculatory system during exhalation.

The disadvantage of this system is the complicated functioning as regards feeding of breathing gas, on the one hand via the injector nozzle and, on the other, via the jet nozzle and the ejector nozzle, the operation of the latter nozzles necessitating control by a special control unit for feeding the breathing gas, which makes the construction of the anaesthesia unit very co pli- cated. Moreover, the continuous feeding of gas from a breathing gas source implies that the system becomes overloaded and that breathing gas has to be let out, which is uneconomical and results in an increased pollution load.

DESCRIPTION OF THE INVENTION

The object of the invention is to provide a unit in such a manner that said disadvantages are eliminated, so that the flow is not disturbed by the operation of some valves and that easier cleaning of the unit is obtained by there being no valves which require special measures. Nor is any feeding of gas from a breathing gas source required for maintaining the intended direction of flow and, thus, no complicated control system for such gas is required for such intermittent feeding of gas.

However, in order to ensure that the intended direction of flow in the duct is maintained after all, means in the form of one or more ejectors are arranged for pumping the gas, which transport the gas in the described direction through the absorber. The gas for the operation of the ejector is thus obtained from the duct without additional gas from a breathing gas source being required. The only gas that needs to be added to the system is that consumed during the operation of the unit. Moreover, the ejector assembly is arranged in such a manner that the cleaning of the unit after use is facilitated, as will be evident from the following description of the preferred embodiments .

DESCRIPTION OF FIGURES In the following, two embodiments of the invention will be described with reference to the accompanying drawings in which

Fig. 1 is a schematic view of an anaesthesia unit according to the first embodiment of the invention, and Fig. 2 shows the second embodiment of the invention in the same schematic manner.

PREFERRED EMBODIMENTS

In Fig. 1, the schematic image of the anaesthesia unit according to the invention shows the flow duct for the circular gas flow which is present in all recirculatory systems, and which is here designated 1. The duct 1 has a connection 2 for connecting to the patient's respiratory system, such as through a pharynx tube or a tube down the trachea, or a mask. The absorber which is designated 3 is inserted into the flow path. Besides, there is a connection 4 to a ventilator for breathing support, here designated 5. The ventilator 5 is here shown as provided with a pump-out valve 7 which is adapted to open at a certain pressure in the system and let out surplus gas. Bellows 6 for monitoring the breathing process are adapted in such a manner that they expand and collapse concurrently with the patient's breathing. Moreover, the ventilator is generally provided with an auxiliary device in order to support the patient's breathing, such as a bladder which can be operated manually or a mechanical unit which yields a rhythmic pressure change . Furthermore, there is connected to the duct 1 a supply line 10 for fresh gas, i.e. oxygen and anaesthesia gas, in order to replace the consumed amount of breathing gas fed to the patient, and possibly another additive. The arrow 12 in the duct 1 shows the direction of flow of gas which is exhaled by the patient towards the inlet connection 13 of the absorber 3. The arrow 14 indicates the direction of flow of the inhalation gas to the patient from the outlet side 15 of the absorber. In most prior-art units this direction of flow is ensured by means of one-way valves which are placed in the flow duct 1 approximately where the arrows 12 and 14 are placed and which are adapted to open for flow in the direction of the arrows, but close when the gas tends to flow in the opposite direction. It is thus these valves which are present in previously known units and which are eliminated by the invention.

However, in order to ensure flow in the described direction of flow, a gas conveying device with pumping action is arranged, comprising an ejector device 18. The ejector itself is formed of a gas-outlet opening 19 which is directed in the desired direction of flow and located in a throttle 20 in the duct 1. The opening 19 consti- tutes an opening into an outlet tube 21 from the pressure side 22 to a pump 23, the inlet 24 of which is connected to a tube 25 to the flow duct 1 upstream of the ejector 18. The ejector both receives the gas from and delivers it to the duct 1. In the first place, a construction which allows easy cleaning is chosen for the pump 23. Preferably, the pump is formed as a part which is detachable from the rest of the unit, which has also been indicated in the figure by the outlet and inlet of the pump, 22 and 24, respec- tively, being shown as inserted into the ejector tube 21 and the connecting tube 25, respectively.

It can be assumed that the pump is driven by electric current. Thus, a replacement system is required in order to provide the flow out of the ejector which is to maintain the proper direction of flow in the duct 1, even if the current supply ceased. For this purpose, the ejector tube 21 is provided with a connection 27 which can be connected to the supply line 10 for fresh gas, see the connecting line 28. In the connecting line 28 a three-way valve 29 is mounted, which usually is m the shown position, so that the fresh gas flows directly from the gas containers and through the tube 10 into the duct 1. If the pump 23 is stopped by power failure or another breakdown, the three-way valve can be adjusted m such a manner that the fresh gas flows out of the ejector opening 19 instead and effects circulation of the gas m the duct 1 m the intended direction. In order to make this function, it is assumed that no reverse flow can occur from the connection 27 and through the pump instead of through the ejector opening 19. This is achieved either by the pump having such a construction that it does not allow reverse flow or by means of a one-way valve between the pump and the connection 27. It may be assumed that the flow of fresh gas has to be increased m relation to the normal functioning if it is to be used to maintain the ejector effect. However, this is an emergency measure only.

When using the unit while connected to the patient's respiratory system via the outlet 2, the flow that the pump 23 generates in operation will result in a pumping action according to the ejector principle. This result m a difference m pressure between the duct part upstream of the ejector 18 and the duct part downstream of the ejector m the direction of the absorber 3. The air flow which is thus formed implies that when the patient exhales, the exhalation gas will flow in the direction of the arrow 12 and be passed on through the absorber 3, so that carbon dioxide is absorbed, and will m connection with inhalation after passing the absorber be fed to the patient through the outlet 2, see arrow 14. No addition of gas is supplied by means of the ejector since the pump is connected to the duct 1 via the outlet 25. The exhaustion from the duct that thus takes place results in a certain addition to the pumping action.

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connection of the fresh-gas supply line to the ejectors, cf . the arrangement 27-29 in Fig. 1.

In the now described embodiment, pressure surges from the ventilator through the connection 4 will be counteracted by the pumping action of the ejector 32 and, thus, do not result in reverse flow in the direction of the patient connection 2. In case of low pressure impulses from the ventilator, these will be counteracted by the pumping action of the ejector 33 and do not result in reverse flow in the direction away from the absorber.

In prior-art embodiments of the recirculatory system, the valves and the passive action thereof are, as mentioned above, replaced by active action by establishing a pumping action which maintains the correct direc- tion of flow. This pumping action is established by means of respectively one and two ejectors. Naturally, further ejectors can be arranged within the scope of the invention. By the ejector collecting its gas for operation from the flow duct, no supplementary gas needs to be sup- plied for its work. Since the ejector operates continuously, no device for controlling an intermittent gas flow is required either. When using ejectors for pumping as described, very simple arrangements are obtained in the flow duct, consisting of the inwardly extending ejector tubes and the design of the wall with throttle. Consequently, it will be easy to clean the flow duct by flushing the same and the ejector tubes. The pump may be formed with a simple passage for rational cleaning. It is preferred that the pump does not require any valves as regards its functioning. Alternatively, an exchangeable bacterial filter can be inserted in the inlet pipe to the pump to prevent contamination of the pump.

Apart from this design which is suitable for efficient cleaning, the solution according to the invention gives the patient a more favourable breathing process since the flow of the breathing gas does not need to be used for opening and closing valves, which would result in a certain degree of reverse flow in connection with every opening and closing process. Experience shows that automatic one-way valves are also often unreliable as regards their function. However, an ejector lacks moving parts and is very rugged. Suitable gas pump constructions are available.

The described and shown arrangement as regards the unit constitutes only an example based on previously known arrangements concerning the various components and their connections but can vary within the scope of the invention if the fundamental principle which applies to the recirculatory system is maintained and the central solution of the invention is used, involving maintenance of the predetermined direction of flow through pumping by means of one or more ejectors. Thus, supply of fresh gas may take place in positions along the duct other than after the absorber as shown in the figures. The supply may also take place by means of several connections. It is also possible to let the fresh gas wholly or partly be supplied through the ejector also when the gas pump is in operation. In connection with a possible breakdown of the pump, no reversal of the fresh-gas flow would then have to occur, presumably only an increase of the same for compensation of the breakdown of the pump. The arrange- ment of the suction connection of the gas pump to the duct downstream of the outlet opening in the duct is only shown by way of example. Also other positions of connection to the duct are possible without abandoning the principle of the invention.

Claims

1. An anaesthesia unit operating according to the recirculatory system and thus comprising a duct (1) for circulation of breathing gas from the patient when exhaling and to the patient when inhaling while the gas passes through an absorber (3) of carbon dioxide which is connected to the duct which is provided with a connection (2) to the patient's respiratory system and one or more connections (4) to auxiliary devices, such as a ventilator (5) and one or more connections (10) for supplying fresh gas, such as oxygen and anaesthesia gas, there being arranged, in order to ensure the circular direction of flow in the duct (1) to the inlet (13) of the absorber (3) in connection with exhalation and from the outlet (15) of the absorber in connection with inhalation, at least one gas conveying device (18/32, 33) in connection with the duct (1) to drive the gas by pumping action in said, predetermined direction, c h a r a c t e r i s e d in that the gas conveying device is arranged in the form of at least one ejector (18/32, 33) comprising a throttle (20/36, 37) arranged in the duct (1) with an outlet opening (19/35) arranged in the same, belonging to a gas in- let tube (21/34) for gas from a gas pump (23/39) , the outlet (22/38) of which is connected to said tube (21/34) and the inlet (24/40) of which is connected to the duct (1) •

2. An anaesthesia unit as claimed in claim 1, c h a r a c t e r i s e d in that there is connected to said connection (10) for supplying fresh gas to the duct (1) a connecting line (28/44) to the tube (21/34) which is provided with the outlet opening (19/35) , so that the supplied fresh gas thus can be used for driving the pres- ent ejector (18/32, 33) in case of insufficient function of the gas pump (23/39) .

3. An anaesthesia unit as claimed in claim 2, c h a r a c t e r i s e d in that the connection (10) for supplying fresh gas to the duct (1) is connected, on the one hand, directly to the duct, and, on the other, to the connecting line (28/44) to the tube (21/34) provided with the outlet opening (19/35) of the ejector by means of a reversing valve (29) , so that the fresh gas alternatively can be fed to the duct directly or to the connecting line for letting out fresh gas through said opening (19/35) , thereby causing the pumping action of the ejector and enabling maintenance of the predetermined direction of gas flow in the duct (1) when the function of the gas pump (23/39) has ceased.

4. An anaesthesia unit as claimed in any one of claims 1-3, c h a r a c t e r i s e d in that the inlet tube (21/34) of the ejector (18/32, 33) and a conduit for its inlet (24/40) are formed as parts which are integrated with the tubing of the duct (1) , whereas the gas pump (23/39) is formed as a component which is separable from said parts of the ejector.