VALVE MEANS SPECIFICALLY INTENDED FOR ANAESTHETIC SYSTEMS

Abstract: Valve means for an anaesthetic system which comprises an inhalation means, such as an anaesthetic mask, a gas supply system for the supply of a mixture of gases containing oxygen and an anaesthetic gas, at least one valve (64, 65) for regulating the gas flow in the system and an outlet (67) or the like for the controlled discharge of used gas. The valve means incorporates a sensing means (53, 56) so arranged as to sense the gas speed and the direction of the gas flow in a gas duct inside the system, and a power means (61) so arranged as to cause the valve to open when the speed of the gas in a pre-determined direction exceeds a certain value. The sensing means incorporates a duct (53) with a constriction (56) and on either side of the construction inlets to two lateral ducts (57, 58). The power means (61) is so arranged as to cause the valve (64, 65) to move to its different positions by utilizing the higher pressure which arises because of the direction of flow of the gas and its rate of flow on the arrival side of the constriction in relation to the lower pressure downstream of the constriction. It takes the form of two chambers (59, 60) which are connected to the lateral ducts (57, 58) and which are separated by a movable organ such as a membrane (63) to which the valve is connected. The difference in pressure which occurs in the sensing means as the gas is flowing thus provides control of the valve.

Description: Valve means specifically intended for anaesthetic systems Technical Field: The present invention relates to a valve means specifically intended for anaesthetic systems which comprises an inhalation means, such as an anaesthetic mask, a gas supply system for the supply of a mixture of gases containing oxygen and an anaesthetic gas, at least one valve for regulating the gas flow in the system and an outlet or similar for the controlled discharge of used gas. Description of the Prior Art: A number of different approaches are applied to anaesthetic systems. In the case of the least developed system a fresh anaesthetic mixture is supplied each time the patient inhales. On every exhalation the exhaled volume of gas is removed via an overspill valve without being utilized. The level of the supply of fresh gas required corresponds to about 100 ml/kg per minute (kg = patient's weight). The exhaled gas mixture may be divided up into two parts, however, being on the one hand that part which reaches the pulo onary alveoli, where an exchange of gas with the blood takes place with oxygen being removed from the gas mixture and with carbon dioxide being added and with the simultaneous absorption of a certain amount of the anaesthetic gas present in the mixture, and on the other hand that part which only reaches the upper air passageways and the wind pipe as far as the alveoli. In the latter part, the so—called dead—space volume, no gas exchange takes place, which means that once the inhalation phase has ended and the exhalation phase has begun, no carbon dioxide will be present in this gas volume, and essentially no oxygen or anaesthetic gas will have been consumed, either. If none of the exhaled quantity of gas is recovered, then large unused quantities of the gas mixture will have to be replaced by fresh gas. In a more developed system, the so—called circular system, the exhaled gas is caused to pass through a carbon dioxide absorber and it is possible in this way to recover a gas mixture which is so free from carbon dioxide that it can be returned to the patient. The inhaled volume in this case need not consist in its entirety of fresh gas, and a small, supplementary flow is all that is required. This system is quite complex in nature and calls for constant attention to be paid to the carbon dioxide absorber. With a view to being able to recover the unconsumed gas mixture from the exhalation volume without having to make use of an unmanageable absorber, systems with double gas ducts have also been developed. An attempt has been made in this way to catch the first, unconsumed volume and to keep it in a reservoir for re—inhalation, whereas the last volume to be exhaled from the alveoli is discharged. Irrespective of the nature of the system, a valve is needed for the discharge of any surplus gas. The overspill valve may be of two types: 1. Pressure—controlled; that is to say a spring—loaded valve disc which opens at a certain positive pressure within the anaesthetic system. This is the more usual type. 2. Volume—controlled, in which the valve disc is closed in the event of a positive pressure arising rapidly within the anaesthetic system. This solution offers the advantage that the system exhibits the same performance characteristics for both 'controlled* and spontaneous respiration. Technical Problem: Those problems which are associated with the types of valve described are that in the case of Type (1) the performance characteristics of the anaesthetic system differ depending on whether the patient is breathing spontaneously or the anaesthetist is •controlling* his breathing (i.e. looking after his breathing for the patient) and that the valve requires manual adjustment, making it more difficult to use and creating the risk of operator error, whereas in the case of Type (2) the disadvantage is that positive pressure within the system which may arise for any one of a number of reasons, for example the rapid arrival of fresh gas, the patient coughing or 'irregular controlled breathing', can cause the valve to become locked in the closed position and can give rise to high positive pressures with the associated risk of lung rupture. Solution: The valve means contains a sensing means so arranged as to sense the gas speed and the direction of the gas flow in a gas duct inside the system, and a power means so arranged as to cause the valve to open when the speed of the gas in a pre—determined direction exceeds a certain value. The sensing means has a duct with a constriction and on either side of the constriction inlets to two lateral ducts. The power means is so arranged as to cause the valve to move to its different positions by utilizing the higher pressure which arises because of the direction of flow of the gas and its rate of flow on the arrival side of the constriction in relation to the lower pressure downstream of the constriction. It takes the form of two chambers which are connected to the lateral ducts and which are separated by a moving organ, such as a membrane to which the valve is connected. The difference in pressure which occurs in the sensing organ as the gas flows past thus provides control of the valve. Advantages: According to the present invention there is provided a valve means which is suited to use in anaesthetic systems of various types and which in such a case will exhibit great reliability against malfunction, such as becoming locked in a closed or open position, and which has an automatic function making manual adjustment unnecessary. Description of the Drawings: Illustrated in the accompanying drawings is the valve means in accordance with the invention in two applications in anaesthetic systems. The means is described below. The Figures are numbered 1 and 2, each of which illustrates in somewhat schematic form the different component parts of an anaesthtetic system, although in order to provide the maximum clarity neither the proportions nor the relative sizes are correct, with two variants of the valve means being shown. Description of the Preferred Embodiments: As shown in Figure 1 an anaesthetic system exhibits a hose 'BUR OMPI ■ ^iVATl system 1 with a first connecting piece 2 and a second connecting piece 3 and a three—way connector 4 . The three— ay connector is connected via two of its branches 5 and 6 on the one hand to a first hose 7 which terminates at the connecting piece 2 , and on the other hand to a second hose 8 which terminates at the connecting piece 3 . A third branch 9 of the three—way connector 4 is so arranged as to constitute a connecting stub for the inhalation means via which the anaesthetic mixture is supplied to the respiratory tract of the patient. Such a means may consist of a mask or a tube. Such means are already well known, however, and do not require more detailed description here. The connecting pieces 2 and 3 are in turn connected to a part of the anaesthetic system referred to below as the control device 10 . The connecting piece 2 is in this case connected to a stub 11 which leads to a duct 12 which, at its end opposite to that of the connecting stub 11 terminates at a connecting stub 13 . The duct 12 exhibits a constriction 14 . At a point between the constriction 14 and the connecting stub 11 there discharge into the duct on the one hand a connecting stub 15 and on the other hand a lateral duct 16 . At a point between the constriction 14 and the connecting stub 13 there discharges a lateral duct 17 . The connecting stub 15 is intended for a hose (not shown) for the supply of fresh gas, this being a mixture of an anaesthetic gas and oxygen from a pressurized container. A means for the supply of the anaesthetic gas mixture constitutes alongside the hose system 1 , the anaesthetic mask or the like and the control device 10 the fourth part of the system. Such gas supply systems are already well known, however, and do not require more detailed description in this context which consists of the valve means in accordance with the invention. The ducts 16 and 17 both lead to a valve means 20 , of which the duct 16 leads to a first chamber 21 and the duct 17 to a second chamber 22 . The chambers 21 and 22 are separated from each other in a gas—tight manner by means of a membrane 23 which supports a rod 24 . As the rod 24 passes through the walls 25 and 26 of the chambers 21 and 22 , there are present in these walls "BUR ...O sealing membranes 27 and 28 . That end of the rod 24 which projects from the chamber 22 via the membrane 27 is fitted with an actuating means 29 . That end of the rod 24 which projects from the chamber 21 via the membrane 28 is situated inside a third chamber 30 which is enclosed by a wall 31 . This end of the rod supports a valve disc 32 which is capable of interacting with a valve seat 33 . The valve disc and thus also the rod 24 are loaded in the direction of the valve seat 33 by means of a weak spring 34 . The valve seat 33 discharges via a duct 35 into a connection stub 36 which supports the connection piece 3 , and the duct 35 is thus connected to the hose 8 . Into the third chamber 30 there discharge a further two ducts, these being a duct 37 which terminates at a connecting stub 38 and a duct 39 which terminates at a connecting stub 40 . The connecting stub 38 is in turn intended to be connected to a container for the collection of used gas, inside which gas can be stored during the exhalation phases. The stub 40 is designed to be connected to a hose for the removal of used gas. The hose is connected for this purpose in a conventional fashion to a ventilation system (not shown). The remaining connection to the duct 12 , being the connecting stub 13 , is arranged for the connection of a so-called respiration bulb. A bulb of this kind consists of a bag 42 , usually of rubber, which operates between a more or less collapsed state and a full state. No inflation of the material in the bag 42 occurs during operation, however, since the system is not designed to operate at pressures which would be capable of producing such inflation. The patient's breathing is indicated by the movements of the bulb, and inhalation can be assisted by the application of pressure around the bag. This means, too, is already well known within this field. As may be appreciated from the description given, the space referred to below as the primary space, which is represented by the patient's pulmonary alveoli, the patient's respiratory tract and the aforementioned means in the form of a mask, a pharynx tube or the like, discharges into the three—way connection 4 and is connected to two spaces, one of these being a first space 44 represented by 'BU E __OA.PI , W1PO the hose 7 , the connection piece 2 , the duct 14 and the respiration bulb 42 , to which space are also connected the two spaces 21 and 22 in the valve means 20 . This space 44 is in turn connected to the gas supply system via the connecting stub 15 . To the primary space, which consists of the respiratory system of the patient, there is connected via the three—way connection 4 and parallel with the space 44 a second space 45 , represented by the hose 8 , the connecting piece 3 and the duct 35 . The space 45 is also capable of connection via the valve seat 33 to the third space 30 in the valve means 20, from which, as has already been mentioned, the gas can be discharged freely. If it is assumed that inhalation is about to start and that for this purpose the space 44 is filled with an unused anaesthetic gas mixture, then inhalation will cause this gas mixture to pass via said three—way connection 4 into said primary space. The gas mixture is taken for this purpose from the bulb 42 , said gas mixture being obliged to pass via the duct 12 . The supply of fresh gas via the connecting stub 15 is, in fact, regulated in such a way that the quantity of gas supplied in this fashion is insufficient to provide the flow which enters the patient during inhalation. As the gas flows through the duct 12 , its speed will be increased in the constriction 14 , in so doing creating a negative pressure in the constriction and immediately after it in relation to the pressure at the arrival side, where gas is flowing from the bulb 42 and up to the constriction 14 . The pressure inside the space 21 in the valve means 20 will thus be lower than the pressure inside the space 21 . This means that the valve disc 32 will be in contact with the valve seat 33 , and the force generated by the difference in the gas pressures will be assisted by the force of the spring 34 . The valve disc 32 thus makes a seal against the valve seat 33 , preventing any flow of gas via the hose 8 , and the volume of gas in the space 45 will be kept inside that space. As the subsequent exhalation starts, the valve 32, 33 will still be closed; the spring 34 would still exert initial pressure even if the rod 24 were not to be influenced by a difference in pressure to either side of the mebrane 23 . This means that the gas mixture which flows in via the three—way connection 4 will not be forced into the hose 8 , since the counterpressure within that branch, the space 45 , through the closed valve is higher than in the space 44 connected to the hose 7 . It has already been stated that a gas mixture is taken from the bulb 42 during inhalation, causing the bulb to be in a collapsed state when the inhalation phase starts so that the exhaled gas mixture can then flow rapidly into the space 44 until the bulb has been filled. This direction of gas flow will, however, create a pressure situation in the ducts 16 and 17 which is the opposite of what was the case during inhalation. Thus the pressure inside the first space 21 will be higher than the pressure in the second space 22 , which means that the rod 24 and thus the valve disc 32 will be acted upon by a force in a direction running away from the seat 33 . This means that, once exhalation has continued for a certain time, the valve disc 32 will be lifted from the seat 33 , causing the counterpressure inside the space 45 to become very low, and lower than inside the space 44 . The remaining gas mixture exhaled from the primary space will thus be diverted into the hose 8 and then out through the valve and onwards for eventual discharge via the duct 39 and the stub 38 . Any gas which during the exhalation period fails to find its way into the ventilation system will flow via the stub 38 to the aforementioned storage volume. This will primarily cause the gas volume trapped inside the space 45 to be forced out by the incoming gas. When exhalation ceases, so that the difference in pressure between the spaces 21 and 22 is no longer able to overcome the force of the spring 34 , the valve disc 32 will again close and the most recently exhaled gas volume will be trapped inside the space 45 . Apart from the fact that the valve opens and releases any excess gas in accordance with the above description during normal exhalation, each direction of gas flow corresponding to that for exhalation past the constriction 14 will cause the valve to open, that is to say if a rush of fresh gas enters the system or if the patient coughs, but without any risk of the valve becoming locked. On the next inhalation the closed valve 32, 33 will again " URE OΛ.PI prevent the gas inside the space 45 from being sucked back into the primary space, in the manner previously described. However, the first part of the exhaled air to flow out will be stored inside the space 44 and will form part of the gas mixture which is inhaled. The function described here thus involves a first volume of the exhaled air being collected inside the control device 10 , mainly in the bulb 42 , whilst a last volume of the exhaled air is discharged. On inhalation, a gas mixture is inhaled which consists on the one hand of the first part of the gas mixture exhaled during the previous exhalation phase, which has been stored inside the control device, and on the other hand of fresh gas supplied since the previous inhalation phase. It is possible, by appropriate adjustment of the system, to achieve a situation in which the first exhaled gas volume which has been stored inside the control device will correspond essentially to the dead—space volume which never reached the alveoli and which accordingly remains unused. The last part to be exhaled, which is gradually discharged via the control device, will, on the other hand, correspond essentially to the gas volume which reached the alveoli and which may thus be regarded as having been used and as being unsuitable for return to the patient. It is naturally impossible to achieve such perfect adjustment of the system that the two parts of the exhaled volume can be separated completely one from the other for re—inhalation and discharge respectively. The ratio of the dead—space volume to the total volume of the respiratory system will be found to differ from patient to patient and is furthermore impossible to measure by practical means to any great degree of accuracy. A patient's breathing may become deeper or shallower, moreover, and a certain amount of mixing will occur within the mass of gas as it flows. However, the preferred level of adjustment is one which will permit a certain proportion of unused gas to be discharged, so that it must be replaced by fresh gas, although avoiding the re—inhalation of used gas containing carbon dioxide. Adjustment of the system to give the desired result is done by adjusting the different volumes in relation to each other and also by adjusting the flow areas. Furthermore, the duct 12 with its constriction 14 and the execution and positioning of the branched ducts 16 and 17 are effected with great care, so that the valve 32, 33 is caused to open once the space 44 is full, said space being suitable to accommodate said first part of the exhaled gas. The valve must permit the discharge of the gas contained inside the space 45 to take place sufficiently rapidly to prevent the creation of a counterpressure at a level which could upset the function. It is also important for the valve 32, 33 to close rapidly when the inhalation phase starts, as the used gas could otherwise flow back into the space 45 . The pressure and the intervals at which the valve 32, 33 operates are determined by a number of factors such as the volume of the spaces 21 and 22 , the area of the mebrane 23 and the force of the spring 34 , and also the operating pressure inside the space 45 acting against the valve disc 33 . The process is further influenced by the moving masses of the valve, and these should be kept as small as possible. The actuating means 29 on the rod 24 permits the manual opening of the valve disc 32 , so that thorough ventilation of the space 45 can be achieved, for example at the start and at the end of anaesthesis. As will have been appreciated from the above description, the fundamental ideas of invention for the system in accordance with the typical embodiment are that the exhaled quantity of gas is caused to pass over a period into two spaces, with the first part to be exhaled being caused to pass into a first space for re—inhalation, and with the last part to be exhaled being caused to pass into a second space for discharge. This control of the portions of gas is effected by means of the valve in accordance with the invention, which always opens during exhalation and/or in the event of occasional high flows of fresh gas into the system. This valve is incapable of becoming locked in such a way that large static pressure loadings will arise inside the patient's thoracic cage, and no manual adjustment is required. The control function is achieved by the valve means sensing the direction of flow in ducts associated with the first space, in such a way that the inward flow during exhalation will cause the gas flow to be switched to the second space after the elapse of a certain period, whereas the outward flow from the first space during inhalation will cause the second space to be closed in such a way that no gas is able to flow from it. As has already been stated, the special valve in accordance with the invention is provided for the aforementioned sensing of the direction of flow. This valve regulates the flow in relation to the second space in such a way that an inward flow cannot occur during the first exhalation period, causing the gas flow to be switched over to the first space, and in such a way that the outward flow of gas from the second space to the patient is essentially prevented, although an outward flow for eventual discharge is permitted. This control of the flow in relation to the second space takes place in accordance with the above description by means of a valve in the inner part of the second space, said valve when it is closed preventing both the inward flow into the gas—filled space and the outward flow from same, and when in the open position permitting the discharge of gas from the space, at the same time allowing gas to flow in. The valve means 20 illustrated in Fig.1 can be modified in accordance with Fig. 2 so that it can be used in other anaesthetic systems such as the circular system or the Hapleson D system. In the embodiment in accordance with Fig. 2, a stub 50 is connected to an anaesthetic system (for example, the circular system or the Mapleson D system). The stub 50 is connected by means of a duct 53 to a second stub 54 which supports a respiration bulb 55 . The duct 53 exhibits a constriction 56 , from the end of which facing the stub 50 there runs a lateral duct 57 , and from the end of which facing the stub 54 there runs a lateral duct 58 . The lateral ducts 57 and 58 each discharge into a chamber 59 and 60 respectively and into a valve means 61 . The valve means 61 is in principle of the same type as the previously described valve arrangement 20 and thus exhibits a body 62 in which the chambers 59 and 60 are situated, a membrane 63 which forms a partition wall inside the body 62 between the SUR fa i ^.rv chambers 59, 60 , and a valve seat 64 which can be sealed by means of a valve body 65 which is connected by means of a rod 66 with the membrane 63 . The valve seat 65 provides a connection between the chamber 60 and a discharge duct 67 for used gas, which may be compared with the discharge ducts 38, 39 in the first embodiment. A weak spring 68 endeavours to keep the valve body 65 closed and thus in contact with the seat 64 . In this embodiment, as in the previous embodiment, fresh gas is supplied, for example via a stub 69 , in the form of a suitable flow to an anaesthetic system of an appropriate type. The valve will open in the presence of a sufficiently strong or rapidly increasing gas flow in the direction of the respiration bulb past the constriction 56 , irrespective of whether the gas flow is caused by exhalation, coughing or a high rate of flow for the fresh gas. On exhalation, therefore, the exhaled gas will flow in via the stub 50 and onwards to the duct 53 . Because of the higher pressure ahead of the constriction 56 the pressure inside the chamber 59 will be higher than that inside the chamber 60 , which means that the membrane 63 will cause the valve body 65 to open. In this way the gas flowing past the constriction 56 will be able to exit freely through the discharge duct 67 via the lateral duct 58 and the chamber 60 . Only when exhalation has ended will the valve close, when the fresh gas will fill the respiration bulb 55 and the hose 52 . In the event of assisted breathing being provided by compressing the respiration bulb 55 , this will result in a higher pressure inside the chamber 60 than inside the chamber 59 , causing the valve to remain closed so that no fresh gas is lost. The valve means described here has been found to work well and is of relatively simple execution, having been derived from the technical field already familiar in this context, in this way facilitating the understanding of the apparatus and its maintenance by anyone concerned with its operation. It is for this reason exceptionally well suited for use as a component in anaesthetic systems which, as has already been stated, can be of different types.

Claims: Patent Claims: 1. Valve means intended in particular for an anaesthetic system which comprises an inhalation means, such as an anaesthetic mask, a gas supply system for the supply of a mixture of gases containing oxygen and an anaesthetic gas, at least one valve (32, 33; 64, 65) for regulating the gas flow in the system and an outlet (37; 67) or similar for the controlled discharge of used gas, c h a r a c t e r i z e d in that there is provided for the purpose of causing the valve (32, 33; 64, 65) to open and close a control means (12, 14, 20; 53, 56, 61 ) which incorporates a sensing means (12, 14; 53, 56) so arranged as to sense the gas speed and the direction of the gas flow in a gas duct inside the system, and a power means (20; 61) so arranged as to cause the valve (32, 33; 64, 65) to open in the system when the speed of the gas in a pre—determined direction, for instance as the result of deep breathing or coughing by the patient connected to the inhalation means or as a result of the controlled generation of a gas flow, exceeds a certain, pre—determined value on its way past the sensing means, and as to cause the valve to remain closed at those times when the aforementioned pre—determined gas speed is not exceeded, for which purpose the sensing means incorporates a duct (12; 53) with a constriction (14; 56) and on either side of the constriction inlets to two lateral ducts (16, 17; 57, 58), and in that the power means (20; 61) is so arranged as to cause the valve (32, 33; 64, 65) to move to its different positions by utilizing the higher pressure which arises because of the direction of flow of the gas and its rate of flow on the arrival side of the constriction in relation to the lower pressure downstream of the constriction, and takes the form of two chambers (21, 22; 59, 60), each of which is connected to one of the aforementioned lateral ducts (16, 17; 57, 58) and which are separated by means of an organ capable of moving towards and away from the respective chambers, such as a membrane (23; 63) to which the valve (32, 33; 64, 65) is connected, so that the aforementioned difference in pressure which occurs in the sensing means will cause the organ to move and in so doing will provide control of the valve. 'BUR __OA. - WI NA 2. Valve means in accordance with Patent Claim 1, c h a r a c t e r i z e d in that the membrane (23) is so arranged as to actuate the valve in conjunction with an initial force, for example a spring force, in such a way that a flow in one direction will endeavour to cause the valve to open against the effect of said initial force, whereas a flow in the opposite direction will endeavour to cause the valve to close with the help of said initial force as a result of the difference between the pressures in the two chambers (21, 22) created by the flow past the constriction. 3. Valve means in accordance with Patent Claims 1 or 2, c h a r ¬ a c t e r i z e d in that the sensing means (12, 14; 53, 56) is connected with that part of its duct (12, 53) which is situated to one side of the constriction (14; 56) to an expandable and contractable bulb (42) and in that the power means (20; 61) is so arranged as to actuate the valve (32, 33; 64, 65) which is positioned in the aforementioned outlet (37; 67) so that it is closed when a controlled gas flow is generated by compressing the bulb. " UREAi -OMPI ♦ 5 WIPO 2&?NAT

Inventors: STENQVIST OLA, STENQVIST, OLA
Applicants: VIMED HB, VIMED HANDELSBOLAG
Application year: 1984
Main classification: A61M17
IPC codes: A61M16