CLOSED CIRCUIT ANAESTHESIA DEVICE

Abstract: The closed circuit anesthesia method and device pro­ vides for a casing including a separation between a primary side and a secondary side in the form of a volume-­ displacement detector (1) which preferably is a dry spirome­ ter. Means (13) are provided for detecting the composition and the volume of the respiratory air and connections (19, 20) for supply of required gases. The secondary side is connected to a patient circuit via two branches (8, 9) containing a car­ bonic acid absorber (10). The output information of the volume-displacement detector (1) is supplied to a control unit (13) for communication with the gas supplies (19, 20). The system comprises an oxygen analyzer (15) and may addition­ ally contain further analyzers (16) for other gas components. The closed anesthesia system of the invention has the advan­ tages of considerably lowering the total consumption of highly cleaned gases like oxygen and narcotics in comparison to open and semi-open systems. Also the narcotic gases stay warmer and more humid and the oxygen consumption as well as the amount of narcotic taken up by the patient can be determined equally allowing a better control of the depth of anesthesia.

Description: Closed circuit anesthesia method and device The invention relates to an anesthesia device with breathing-return, comprising a casing and a separation between one (primary) side, which is provided with a connection to a respiration control machine, and the other (secondary) side which is provided with a connection for the patient, means for detecting the composition and the volume of the respiratory air and connections for the supply of the gases required, said secondary side comprising two branches one of which is provided with a carbonic acid absorber with a blower. For administering narcosis a so-called semi-open system presents to extremely important disadvantages. In the first place a particularly great amount of gases is used, which is very expensive. In the second place the great surplus of gases enters into the operating room. The socalled semi-closed systems do obviate these objections in part, but nevertheless the amounts of gas used are quite * considerable. Closed circuit anesthesia is also being applied, but only by a small number of anesthetists. In order to give some idea it can be stated that with semi closed systems in practice 2 to 3 liters of oxygen per minute are supplied and 4 to 6 liters of laughing gas. The real consumption by the patient is in the order of 1/4 liter of oxygen per minute and, initially, 1.5 to 2 liters of laughing gas, within a few minutes decreasing to a few hundred milliliters per minute. Anesthetists for reasons of medical security with the semi-closed systems feel compelled to apply such great surplus amounts; even when taking amounts of 2 liters of oxygen and 4 liters of laughing gas per minute, this implies cost of the gas of about Hfl. 24.- per hour. The adverse health effects don't exist for patients who are exposed once, during several hours at maximum, to the effect of narcotics. The problem is with the operating room personnel, who breath the gases from the narcotizing apparatus entering the atmosphere in the operating room during the greater part of their full working time. Clear indications exist that this causes diseases, so that both in the Nehterlands and in other countries legislation is being prepared for the protection of personnel in operating rooms. One of the possible solutions for the problem is the provision of an exhaust installation, the cost of which per group of operating rooms in a hospital are in the order of Hfl. 250.000.-. The advantages of a fully closed anesthesia system have been recognized long since. In the first place the amount of gases required is reduced to what is taken up directly by the patient. This means that the abovementioned cost of Hfl. 24.- per hour can be reduced to Rfl. 2.- per hour, for oxygen and narcotic gas. The problem of pollution of the atmosphere in the operating room is as a matter of course non existent with a fully closed system. Apart from these two external factors, which are very striking, there is a great series of advantages from the point of view of the patient and the medical treatment, respectively. Some of these are: in a closed system the narcotic gases stay warmer and more humid, cold and not-humid gases in a nonclosed system entailing a considerably greater risk of problems with the lungs. With a closed system the oxygen consumption can be determined. The amount of narcotic taken up can be determined accurately, which allows a better control of the depth of the anesthesia. Still further advantages from the medical point of view can be found in the anesthesiological literature. Despite the manifest advantages, closed systems are still applied by a small number of anesthetists yet, to which those who consider the adavantages to prevail over the disadvantages unavoidable up to now. These disadvantages can be summarized concisely as the necessity of an additional assistant for the continuous manual control of the amounts of gas and the manual steering of respiration, the risk of errors in the amounts administered, particularly by a faulty reaction to phenomena occurring unexpectedly with the patient under treatment. The invention starts from a system connected to a machine for controlling respiration, for shortness called ventilator. With the known semi-open systems and the semiclosed systems modulating is done with a machine, but it can also be done by hand, whilst up to now with closed systems modulating is done exclusively by hand. The separation between the primary side of the device, connected to the respiration control machine which thus takes care of rhythmically pressurizing the secondary side and this - secondary side, which is connected to the patient's respiratory system, comprises a balloon included in a box.- The interior of the balloon is connected to the secondary side. When modulating is done manually, it is done by squeezing the balloon by hand. The object of the present invention is to provice a device of the fully closed type, capable of functionning fully automatically, and this, as a matter of course, with complete security. In this way the closed system becomes applicable at large scale, so that the advantages of this system can be gained everywhere. Basically the device according to the invention is characterized in that the separation between the primary and secondary sides comprises a volume-displacement detector, the information output of which is connected with the control unit for communication with one or more of the supplies for the gases. By a volume-displacement detector there is to be understood every device, which, when a volume changes, permits to detect the change of volume by the displacement of an appropriate element. In this way it becomes possible to continuously determine how much of the gases have been used by the patient, and thereby it becomes possible also to adjust this use continuously. This idea can be realized in practice with a greater accuracy and reliability than is the case with a closed anesthesia circuit having manual operation. As a volume-displacement detector, for example a bellows can be employed. There is a preference, however, for a device comprising a cylindrical piston which is sealingly movable with respect to a cylindrical casing wall by means of a rolling seal. More particularly, it is possible to use for this purpose a dry spirometer of a commercially available type. These apparatus, which have been merchandized by the applicant company long since, have an extremely low inertia, and therefore, a very fast response. When this apparatus is used, it is possible to obtain, already from the first inhaling stroke after the beginning of administering the narcotic gas, information about the anesthetic process, which is useful for the virtually perfect control of the process. For a good understanding it is of importance to note that the anesthetic effect of narcotic gas is dependent on the partial pressure which this gas reaches in the arterial blood. The rate at which this happens is determined, apart from the alveolar ventilation, by the difference in concentration between the interior of the lungs and the blood flow. At the beginning of the narcosis, therefore, the narcotic gas is taken up at a fast rate; 2 to 3 liters of laughing gas per minute as the case may be. After 5 or 6 minutes, the narcotic gas con- tent in the blood has reached 90 % already of the maximum value attainable. The take-in which is initially very high, has then decreased already to the order to 250 ml per minute and will go down still a little further to a more or less constant value which is required as a compensation for the evaporation of the narcotic gas occurring continuously at the surface of the body. Form the course of the take-in of the narcotic gas, the anesthetist will be able to draw particularly interesting conclusions about the patient, upon which he could react immediately to control the whole anestetic process. Up to now, it was a common habit, at the start, to "wash the patient's blood in", with several liters of narcotic gas, to thereupon close the system. But then the opportunity has passed already to obtain the most important information. With the system according to the invention, which is completely closed as from the start, all important information from the first respiration stroke after the start of administering narcotic gas, can be recorded, processed and presented in a useful manner to the anesthetist. Resuming, it means that with the device according to the invention, the anesthetist has a better control of the manner in which the patient reacts on the narcotic gases administered. The device according to the invention provided in known manner with an oxygen sensor, is preferably realized in this way that the information output of the oxygen sensor is connected with the control unit for communication with the oxygen supply in such manner that there is a continuous supply of the amount of oxygen required as an average, and that the end of every expiration phase the volume lost as compared with the previous stroke is determined and the information output communicates, via the control unit, with the supplies for the gases in such manner that the lost volume detected is immediately replenished in form of narcotic gas. Apart from this, the invention offers possibilities for measuring a considerable number of parameters which are of great medical importance. A special aspect is the risk of the arising of leaks in the system. With the closed system, as it has hitherto been applied, with manual respiration control, accidents could be caused, as a result of unobserved leaks in the system, because of a reduction in the oxygen concentration. With the system according to the invention this cannot happen anymore. In case of leakage the ratio between oxygen and narcotic gas remains constant. In case of changing the connections for narcotic gas and oxygen, the valve for the narcotic will automatically close and within a short period the system will contain oxygen only. The device according to the invention also has features which make it fit to be used as an auxiliary respiration apparatus, particularly for intensive care. In this case the information outputs of the volume-displacement detector are connected with the oxygen supply in such manner that the volume lost with every stroke is entirely compensated for in form of oxygen. By the addition of a device capable of building up pressure on the primary side, the device may also function as an independent respiration control apparatus. The invention also relates to a method of administering closed circuit anesthesia in which use is possibly made of already existing equipment, particularly when an existing spirometer is put in between a respiration control machine and a narcosis device. The methode according to the invention is characterized in that a continuous measurement is performed of the patient's expiration volume and in that at the end of each expiration phase the volume lost as compared with the previous stroke is determined and this volume is immediately replenished in form of narcotic gas. Preferably the method is realized in this way that a continuous measurement of the oxygen is performed and the amount consumed is continuously replenished. The invention will now be clarified with reference to the accompanying drawing. The single figure shows a diagram of the device. The kernel of the device is the volume-displacement detector, schematically represented here as a dry spirometer 1,# in which a light bell 2 is arranged within a cylindrical casing, while placing a rolling seal 4 in between. The bell and the rolling seal together constitute a complete separation between the primary space, at the left hand side of the figure, which has a connection 5, and the secondary space, at the right hand side, having two connections 6 and 7 respectively. With connection 5 the spirometer can be connected to the respiration control device which may be entirely of known type and which produces volume-displacements. The connections 6 and 7 communicate with two branches 8, 9 of the circuit. In the one branch 8 there is a CO2-absorber 10 and a blower 11, which ensures that there can only be circulation in the sense indicated. The two branches 8 and 9 meet again at 12, where the connection to the patient can be made. The control unit 13 is provided with several information inputs. In the first place it receives data from the information output 14 of spirometer 1. Next in any case also detected are data from the oxygenanalyzer,schemKically indicated by 15 and eventually also the data from carbon dioxide analyzer 16. The two or three of them detect the gas in the circuit. Furthermore, as a matter of course, there is an opportunity to feed certain set-values to control unit 13. An information input 17 may serve for the set-value of the volume of the system and input 18 for the set-value of the oxygen concentration. Outputs from control unit 13 will at least comprise an output to a control valve 19 for the narcotic gas and an output to a control valve 20 for the oxygen. Under command of the respiration control machine, via the oscillating spirometer bell 2, the respiration of the patient will be kept under control. On the secondary side the system, together with the contents of the lungs and the further respiratory system of the patient, is closed. All carbonic acid gas expired by the patient is absorbed. From the analysis of the composition of the gas it can be determined how much oxygen the patient consumes as an average, and this amount consumed is replenished continuously. Subsequently, at the end of every expiration stroke of the patient, the lost volume is determined by means of spirometer 1, and this is replenished immediately by narcotic gas. Then the whole operation of the device is automatic, although the anesthetist, as a matter of course, does have the opportunity to change the set-values for the various parameters, depending on the anesthetic method which he wants to apply, the development of the process, particularly the reactions of the patient, etc. Of course, all information taken can be processed and made visible in any desired manner, and also be recorded in view of noting the patient's history. Apart from the essential features of the system, described above, there is a possibility to determine a great number of parameters which are of medical interest. A first example of these has been represented in the drawing, in form of a supply valve 21 for helium gas. This is a neutral gas, offering the possibility to determine the FRC (functional residual capacity) of the lungs. The course of consumption of the narcotic gas, for example laughing gas, and of the oxygen consumption provides information, e.g. about the respiration, the circulation, the heartminute volume and, more generally, the patient's entire metabolic condition. Also in the vicinity of connection 5 one may simply add a device for introducing, during a short time, an overpressure at the primary side of the system, for example in the order to 5 cm head of water (which device may be a tube submerged a 5 cm depth in an amount of water). The ratio between the change of colume Av as a result of this pressure difference A p is a measure for the lung compliance, and for A FRC in relation to A p The system can be provided with an aperture to observe the effects of a very fast concentration change of the narcotic gas. As a matter of course other gas-analyzers can be connected with the system. Resuming, the device according to the application permits a much better control of the patient, particularly on what his body does with the narcotic gases administered, and this better than with the closed circuit anesthesia as applied up to now. These advantages add to the most important advantages, as discussed in the preamble, of a saving in gas consumption which per operating room per annum, on the basis of a normal weeks working time, lies at about Hfl. 40.000.- per annum, and furthermore, the prevention of pollution of the operating room atmosphere. The device according to the application also has properties which make it fit to be employed just as an auxiliary device for respiration control, particularly for intensive care. In this case the information outputs of the volumedisplacement detector are connected with the oxygen supply in such manner that the volume lost with every stroke -is replenished entirely in form of oxygen. By addition of a device capable of building up pressure at the primary side, the device is capable of functioning as an independent respiration control apparatus.

Claims: CLAIMS 1. Anesthesia device with breathing-return, comprising a casing and a separation between one (primary) side, which is provided with a connection (5) to a respiration control machine, and the other (secondary) side which is provided with a connection (6, 7) for the patient, means (13) for detecting the composition and the volume of the respira- - tory air and connections (19, 20) for the supply of the gases required, said secondary side comprising two branches (8, 9) one of which is provided with a carbonic acid absorber (10) with a blower (11), c h a r a c t e r i z e d i n t h a t the separation between the primary and secondary sides comprises a volume-displacement detector (1), the information output of which is connected with the control unit (13) for communication with one or more of the supplies (19, 20) for the gases. 2. Device according to claim 1, c h a r c t e r i z e d i n t h a t the volume-displacement detector is a dry spirometer (1). 3. Device according to claim 1 or 2, c h a r a c t e r i z e d i n t h a t the volume-displacement detector comprises a cylindrical piston (2) sealingly movable with respect to a cylindrical housing wall (3) by means of a rolling seal (4). 4. Device according to any of the preceding claims, provided with an oxygen sensor, c h a r a c t e r i z e d i n t h a t the information output of the oxygen sensor (15) is connected with the control unit (13) for communication with the oxygen supply (20) in such manner that there is a continuous supply of the amount of oxygen required as an average, and in that, at the end of every expiration phase the volume lost as compared with the previous stroke is determined and the information output (14) communicates, via the control unit, with the supplies for the gases in such manner that the lost volume. detected is immediately replenished in form of narcotic gas. 5. Device according to any of the preceding claims, c h a r a c t e r i z e d i n t h a t the secondary side is provided with a connection (21) for analytic gas, such as helium, such that during the anesthesia the functional residual capacity of the lungs of the patient can be determined. 6. Device according to any of the preceding claims, c h a r a c t e r i z e d i n t h a t the device at the primary side is provided with means for temporarily increasing the pressure of the respiration control machine, such that from the change of volume resulting from this at the secondary side, the lung compliance can be determined. 7. Device according to any of the preceding claims, c h a r a c t e r i z e d i n t h a t it is provided with means to also measure respiration air parameters, processing them, making them readible, and/or registering them such that furthermore, any of the following determinations can be made: - the course of take in of narcotic, - the course of take in of oxygen, - determining the ratio between the change of the func tional residual capacity and the change of pressure. 8. Device according to any of the preceding claims, c h a r a c t e r i z e d i n t h a t , for use as an auxiliary respiration control machine for intensive care, the information output of the volume-displacement detector communicates, via the control unit, with the oxygen supply in such manner that the volume lost with every stroke is fully replenished in form of oxygen. 9. Respiration control apparatus, comprising a device according to any of claims 1 to 8, provided at the primary side thereof with a device for building up pressure. 10. Method of applying anesthesia with breathing return; employing a device which comprises a casing having a separation between one (primary) side, which is provided with a connection to a respiration control machine, and the other (secondary) side which is provided with a connection for the patient, means for detecting the composition and the volume of the respiratory air and connections for the supply of the gases required, said secondary side comprising two branches one of which is provided with a carbonic acid absorber with a blower, c h a r a c t e r i z e d i n t h a t a continuous measurement is performed of the patient's expiration volume and in that at the end of each expiration phase the volume lost as compared with the previous stroke is determined and this volume is immediately replenished in form of narcotic gas. 11. Method according to claim 10, c h a r a c t e r i z e d i n t h a t a continuous measurement of the oxygen content is performed and the amount consumed is continuously replenished.

Inventors: SCHEPP, RONALD, DR.
Applicants: HELLIGE GMBH
Application year: 1984
Main classification: A61M16
IPC codes: A61M16