US3351057A

US3351057A - Patient safeguarding anesthesia apparatus

Info

Publication number: US3351057A
Application number: US370768A
Authority: US
Inventors: Goodyear Chalmers; Edward A Connolly; Caparrelli Frederick
Original assignee: Foregger Co Inc
Current assignee: Foregger Co Inc
Priority date: 1964-05-28
Filing date: 1964-05-28
Publication date: 1967-11-07
Anticipated expiration: 1984-11-07

Description

1967 c. GOODYEAR ETAL 3,351,057

PATIENT SAFEGUARDING ANESTHESIA APPARATUS Filed May 28. 1964 5 Sheets-Sheet 2 62 44/1456 gaaa r54? Eon/4E0 A GOA/MOLLY BY Feiot/P/cw am lgfiu ATTORNEY 1967 c. GOODYEAR ETAL 3,

PATIENT SAFEGUARDING ANESTHESIA APPARATUS File d May 28. 1964 5 Sheets-$heet 5 MW z wwa ATToiaNEy United States Patent Filed May 28, 1964, Ser. No. 370,768 11 Claims. (Cl. 128-188) This invention relates to anesthesis apparatus, and more particularly relates to a system adapted for use with a gas anesthesia machine for the purpose of safeguarding the patient in the event of the loss of the oxygen supply to the machine.

Patients undergoing operations in hospitals are now ordinarily anesthetized by one or more gases, administered to them by the use of a gas anesthesia machine in which the anesthetic gas is mixed with oxygen. The anesthetic gas, which may be a single gas, or a mixture of gases, and the oxygen to be mixed therewith are ordinarily supplied from gas pressure cylinders connected to the machine through pressure regulators and control valves which are under the control of the anesthetist. The anesthetist has many functions to perform during the operation, such as constantly checking the condition of the patient and conferring with the surgeon, the actual control of the anesthesia machine being only part of his duties.

It is essential for the safety of the patient that oxygen be available to the machine at all times that his respirator requirements are supplied by the machine. Although such oxygen is ordinarily supplied from multiple, alternatively used pressure tanks, it is possible on rare occasions as by reason of malfunctioning of the pressure gauges, check valves, tubing connectors, and so forth for the oxygen supply to the machine to fail. It is essential to the patients safety that this condition be immediately recognized, and that the supply of anesthesia gas to the patient be immediately cut off so that the patient may be supplied with oxygen from another source.

The system of the invention functions automatically to cut off the flow of anesthesia gas to the patient upon the failure or effective failure of the supply of oxygen to the anesthesia machine. In the preferred embodiment of the invention described and illustrated herein it also warns the anesthetist and others in the operating room of the failure of the oxygen supply and upon such occurrence connects the patients breathing circuit to the atmosphere, so that the patient will then be able to breathe the air of the room when the gases from the machine have been cut off.

The invention has among its objects the provision, in a gas anesthesia machine, of a system which functions automatically to cut off from the patient gases from the machine upon the failure of the oxygen supply to the machine.

, Afurther object of the invention lies, in the provision of a system of the type described, of means giving a warning signal to the anesthetist upon such failure of oxygen supply of the machine.

Yet another object of the invention lies in the provision of a system for use with a gas anesthesia machine wherein upon failure of the oxygen supply to the machine the breathing circuit for the patient is automatically connected to another source of oxygen such as the atmosphere.

Other objects of the invention lie in the provision of a patient safeguarding system for a gas anesthesia machine which is characterized by its quickness and sureness 3,351,057 Patented Nov. 7, 1967 of operation, and its simplicity and its economy of manufacture and maintenance.

The above and further objects and novel features of the invention will more fully appear from the following description when the same is read in connection with the accompanying drawings. It is to be understood, however, that the drawings are for the purpose of illustration only, and are not intended as a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

FIG. 1 is a somewhat schematic layout of a gas anesthesia machine incorporating a patient safeguarding system in accordance with a preferred embodiment of the invention;

FIG. 2 is a view in generally axial cross section through a valve actuator employed in the safeguarding system;

FIG. 3 is a view in axial section through the main control valve of the safeguarding system, the movable valve element of such valve being shown in the position which it assumes during normal operation of the gas anesthesia machine; and

FIG. 4 is a view of the main valve similar to FIG. 3 but with the movable valve element in the position it assumes after a failure of the oxygen supply to the machine has occurred.

Turning now to FIG. 1, there is schematically shown therein a gas anesthesia machine which is generally designated by the reference character 10. It is to be understood that such machine is merely illustrative, and that the patient safeguarding system of the invention may be employed with other gas anesthesia machines, such as those, for example, supplied with anesthetics such as ether which require the use of Vaporizers in the machine. The machine 10 is shown as being provided with two alternatively employed oxygen containing cylinders 11 and 11', which are connected, respectively, through check valves 12 and 12 to a common pipe or tube 14 which leads to a pressure regulator 15. The cylinders 11 and 11' are provided with selectively operated shut-off valves 13 and 13' whereby a selected cylinder may be operatively connected to the delivery pipe 14. After passing through the regulator 15, the oxygen proceeds by way of

pipes

16 and 17 to a control valve19 and thence to a flowmeter 20. The delivery end of flowmeter 20 is connected to a pipe 21 which leads to a pipe 22, the latter. pipe being connected by a conventional fitting to the gas inlet port 24 of a main valve 25 of the patient safeguarding system of the invention. Anesthetizing gas or gases mixed with the thus delivered oxygen in the desired ratio are delivered through valve 25, when the valve is in the operative position of FIG. 3, to a flexible tube 27 forming a part of the patients breathing circuit, the delivery end of such tube being connected to a mask or endotracheal tube (not shown) applied to the patient.

One of such anesthetizing gases may be, for example, nitrous oxide which is supplied by alternatively used pressure cylinders 28 and 28'. Such gas is delivered from a chosen cylinder through a shut-off valve 29 and 29',

as the case may be, through check valves 30 and 30' to a common delivery pipe 31. From pipe 31 it goes through a regulator 32 and then to a pipe 34 leading to serially connected control valve 35 and flowmeter 36. The delivery port of flowmeter 36 is connected to the above mentioned pipe 21. Thus by appropriate adjustment of the valves 19 and 35 a predetermined desired mixture of oxygen and nitrous oxide may be delivered to pipe 22 and thence through valve 25 to the tube 27 forming a part of the patients breathing circuit.

The machine is shown provided with a supply of a further anesthetizing gas,

cyclopropane in this case, such cyclopropane being contained under pressure in a cylinder 37 from which it may be delivered upon opening the manually controlled valve 38. Cyclop'ropane flows through pipe 40 which leads to a serially connected control valve 41 and a flowmeter 42. The outlet port from flowmeter 42 is connected to the pipe 21. Thus the gas delivered to the patient is a mixture of oxygen and a selected one of the various anesthetizing gases supplied to the machine or mixtures thereof. The machine may be further supplied with means to flush the patient circuit with oxygen in case of emergency. For this purpose the pipe 17 is continued to be connected to a manually operated flush valve 44, the outlet port of such valve being connected to pipe 22 in advance of the port 24 of valve 25, as shown.

The machine 10 may be provided with a pipe or tube 45'connected to pipe 16, the outer end of pipe 45 having a quick-connect coupling part 46 thereon. Such coupling part, which is conventional, is of such construction that it automatically closes the passage therethrough when it is disconnected from a mating coupling part. The pipe 45 andthe coupling part 46 make it possible manually to connect the machine 10 to a further source of oxygen, such as a valved wall outlet pipe 47, with which hospital operating rooms are conventionally provided, and to control and meter oxygen supplied from such further source by control valve 19 and fiowmeter 20, respectively. The nitrous oxide gas supply portion of the machine is similarly provided with means whereby it may be connected to a still further source of such gas. Thus a pipe 49 having quick-connect coupling part 50 on its outer end is connected to pipe 34 of the machine, as shown. The coupling part 50 permits the machine to be connected to a still further source, such as a valved outlet pipe 51, of

nitrous oxide gas, such further nitrous oxide gas being controlled and metered by valve 35 and meter 36, respectively, and then delivered to

pipes

21, 22 and through valve 25 to the patient.

The patient safeguarding system of the present invention, which includes the valve 25, is shown as being added to the above described machine 10, which normally includes only the elements enclosed within the dot-dash outline. In such known prior machine the pipe 22 is connected directly to the tube 27 of the breathingcircuit asat the slip connection shown at 23. The system of the invention is shown asbeing added to the-conventional gas anesthesia machine as an attachment thereto. It is to be understood, however, that in accordance with the invention the system may. be incorporated inthe machine as an integral part thereof.

The'system shown has a pipe or tube 52 which may be connected to coupling part 46 by a mating-coupling .part 54, so that the tube 52becomes subjected to thepressure of oxygen supplied by the cylinders 11, 11. Alternatively, coupling part 54 may be connected to the valved oxygen wall outlet pipe 47. Connected to the tube 52 is a valve actuator 55, which is responsive to the pressure of the oxygen in tube 52 and the main valve 25 to which it is connected by a pipe or tube 53'so that when the pressure of the oxygen existing in tube 52 falls 'below a predetermined minimum value, at which the oxygen. supply is considered to have failed or substantially failed, the valve' 25 is shifted by actuator 55 from its normal, operating position shown in FIG. 3 to the position shown in FIG. 4; In the position of FIG. 4, the valve 25 connects the'source of oxygen-anesthesia gas mixture flowing through pipe 22 to a vent through an audible signal, and simultaneously connects the patients breathing-circuit to a further source ofJoxygen-containing gas, such as air.

The actuator 55'is shown in detail in FIG. 2. The actuator there shown is one Which'is known as the model CDM 2501 Single Diaphragm Snap Acting Pressure Switch sold by Instruments, Inc., Tulsa, Oklahoma. It is obvious that other available actuators or micro-valves preforming the same functions may be employed in the system of the invention.

Actuator 55 has a body 64, or casing one end of which is provided with a port 65 to which tube 52 is connected. At the other end of body 64 there is provided a valve space 66 therewithin. The actuator 55 has a port 69 at the end thereof opposite port 65 to which tube 53 is connected, and two opposed directed

ports

70, 71 disposed at right angles to port 69. Port 70 communicates directly with the atmosphere. Port 71 is connected to an interior space 74 in actuator 55; space 74, which is in direct communication at all times with tube 52 through port 65, communicates with the inner end of port 65 by a passage 72 in casing 64 which is shown connected to tube 52 in advance of port 65. Diaphragm 75, to be described, has a hole 73 therethrough in alignment with passage 72. It is to be understood that the connection between space 74 and port 71 may be effected, if desired, by a pipe'extending exteriorlyof the casing of the actuator. Within the space 66 in the actuator body there is mounted a movable valve element 67 which is so constructed that when the pressure at port 65 is at or above a' predetermined minimum value (FIG. 2) the valve element is held in one of its stable terminal positions to place

ports

71 and 69 in communication with each other and to close port 70, and that when such pressure at port 65 drops below such minimum value, the valve element is moved into the other of its two stable terminal positions to place

ports

69 and 70 in communication and to close port 71.

The mechanism within actuator 55 for thus'moving the valve element 67 includes a flexible imperforate diaphragm 75 which defines the inner end of the space 74' within the actuator, and is sealed at its edges to the casing of the actuator. Inwardly of the diaphragm 75 there is a' headed diaphragm button 76 which is constantly urged outwardly-from the position shown in FIG. 2 by a coil compression spring 77 acting between the head of the button and an inner tubular spring seat member 78 which is formed integral with the casing of the actuator. Such spring seat member 78 also functions to guide the stem of the button 76 for reciprocation in the casing. The stem of the button is provided with an inclined ramp surface 79 which coacts with the upper end of an actuating lever 80 so that when the button 76 is at its upper terminal position the lever 80 lies in a first one of its two terminal positions, and then, when the button 76 has been thrust downwardly into the position of FIG. 2 by the application of at least a specified minimum pressure to port 65 the lever 80 will be rotated clockwise from such first terminal position through a small angle and into its second terminal position, shown in FIG. 2.

The'valve operating'lever 80 is mounted upon a pivot pin 81 connected to the casing of the actuator, the lower end of the lever 80 forming a port of a toggle 82 which is connected to the movable valve element 67. The construction of the valve element and its actuating means is such that the movable valve element remains stably in either of its two terminal positions until' the toggle has straightened, at which time the movable valve element snaps quickly into its other position.

It will be seen from the above that'the actuator 55 is quickly and accurately responsive to a drop of pressure in tube 52 below the specified minimum value. Under such condition, not only is the tube 52 effectively disconnected from the'sourc'e of oxygen for the machine, but the tube 53, which forms the controlling'link between the actuator- 55 and' the valve 25, is quickly vented to atmosphere,

thereby assuring the rapid actuation of valve 25 from the are held together by means such as longitudinally extending tie rods extending through ears on the casing parts (not shown) and are sealed to each other by O-rings 88, 88' disposed in annular recesses therein, The casing 84 which has its ends closed by transverse cap-like members, has a centrally extending circular cylindrical bore 85 therein. The casing presents inwardly thereof four longitudinally spaced

annular recesses

86, 87, 89, and 90', the first three of which form portions of ports in the Wall of the valve casing. At the bottom the valve is provided with a space 90, which directly communicates with the annular recess 90', and which forms a portion of a pressure responsive means for shifting the movable valve element 91 from the position thereof shown in FIG. 4, to its normal, operative position shown in FIG. 3.

The inner movable valve element of valve 25 is generally designated by the reference character 91. Valve element 91 includes an outer circular cylindrical sleeve 92 which is slidably but sealingly engaged by the above described O-rings 88, such O-Iings isolating the ports of the valve from each other as well as sealing the parts of the housing together. Connected to the bottom end of sleeve 92 is an irnperforate disc member 94 which functions, with the lower end of sleeve 92, as a piston reciprocable in space 90.

Member 94 has a central cylindrical boss 96 thereon which functions to center and seal the lower end of the irnperforate circular cylindrical sleeve 95 which is disposed within sleeve 92 coaxially thereof. Sleeve 92 is spacedfrorn and sealed to an intermediate upper portion of the outer sleeve 92 by an annular spacer member 97. There is thus formed an elongated annular space 98 between the outer

andinner sleeve members

92 and 95. The inner' valve element 91 is constantly resiliently urged towards its lower position, shown in FIG. 4, by a coil compression sprin 99 which is disposed within the inner sleeve 95Iwith its lower end abutting the upper surface of boss 96 and its upper end telescoped over a central tubular member 100, which is mounted on and sealed 'to the upper end member 102 of the casing. The space within the inner sleeve 95 constantly communicates with a whistle 60 and the vent 61 therefor through the central passage 101 in member 100, the port 59, and the pipe 57. The outer sleeve member 92 is provided with three sets of ports spaced longitudinally thereof: an upper set of ports 104, an intermediate set 105, and a lower set of ports 106. Such ports are spaced apart a distance equal to the spacing of

ports

24, 25 and 62 through the outer sleeve 92 of the movable valve element so as selectively to cooperate therewith in the manner shown in FIGS. 3 and4. It should be noted that ports 104 are located beyond the member 97 which closes the upper end of space 98, and that

ports

105 and 106 communicate with such space.

In FIG. 3 the movable. valve element91 is shown elevated into its upper terminal position, which is determined by abutment of the upper end of sleeve 92 against the inner lower surface of member 102 of the housing. Element 91 is thrust into and maintained in such position under normal operating conditions of the machine by the transmission thereto of the pressure of the oxygen in tube 52 through the actuator 55, the port 69 thereof, tube 53, and port 56 of valve 25. The predetermined minimum oxygen pressure, the effective area of the disc 94, and the compressive strength of spring 99 are so chosen that the movable valve element 91 remains in the position of FIG. 3 so long as it is subjected to such minimum oxygen pressure. With the valve in the position shown in FIG. 3, the mixture of oxygen and anesthetizing gas or gases is fed, as shown by dash lines, through pipe 22, into port 24 of valve 25, longitudinally within the space 98 in the valve element 91 to the port 26 of valve 25 and thence to the tube 27 leading to the breathing circuit. In such position of the 6 valve, the port 62 thereof is closed by the imperforate lower end portion of sleeve 92 presented thereto.

Upon the dropping of the oxygen pressure in tube 52 below said predetermined minimum value, the actuator 55 immediately operates, as described, so that port 71 thereof is closed and tube 53 communicates with the atmosphere through the now connected

ports

69 and 70. The oxygen within the space of valve 25 is thus exhausted through tube 53 to the atmosphere, thereby allowing the movable valve element 91 quickly to descend to the position of FIG. 4 under the thrust of spring 99. In such position, as depicted by dash lines in FIG. 4, the pipe 22 now communicates through. aligned

ports

24 and 104 with the space within the inner sleeve 95 and thence through the passage 101 to the pipe 57, the whistle 60 and the vent 61. The tube 27 now communicates through aligned

ports

26 and 105 with the space 98 between the inner and outer sleeves of the movable valve element 91, such space being connected to atmosphere through the now aligned

ports

62 and 106. Thus the patients breathing circuit is connected directly to atmosphere so that now he is immediately able to breathe atmospheric air.

The safeguarding system of the invention is particularly characterized by the speed and positiveness of its action. It is desirable that, upon the failure of the oxygen supply to the machine, the source of anesthetizing gas be disconnected from the breathing circuit and the patient be permitted to breathe atmospheric air in a very short time, on the order of three seconds, in order to prevent possible injury to the patient. The system of the present invention easily meets such requirements. The valve actuator 55 is fast and positive in its action in both closing off tube 52, thereby preventing the escape of anyremaining oxygen in the oxygen supply for the machine, and also permitting the quick venting of the space 90 in the main valve 25 to the atmosphere to permit actuation of the movable valve element 91 thereof into the position of FIG. 4.

The system shown positively isolates the anesthetizing gas or gases or the mixture thereof with low pressure oxygen from the patients breathing circuit upon the fai ure of the oxygen supply for the machine. The whistle 60 or other audible signal is actuated by the anesthetizing gas which continues to flow through pipe 22. until the anesthetist takes action to turn off the supply of such gas. The

patient safeguarding system shown is entirely mechanical, that is non-electrical, in nature, which is important in ananesthesia apparatus employing combustible and/or explosive gases. Thus the valve actuator 55 operates mechanically and controls the main valve 25 through the gas in the tube 53, such tube and the gas therein constituting a mechanical linkage between elements-55 and 25. The audible signal, the whistle 60, is powered mechanically, by the gas supplied thereto from pipe 22 through valve 25 when such valve is in the position of FIG. 4. The patient safeguarding system shown and described thus adds no hazards in the operation of the gas anesthesia ma chine but, instead, removes a possible source of danger to the patient in the use of prior, unmonitored machines. The system may readily be applied to various gas anesthesia machines, as above described,,a nd requires no additional source of power for any of its functions, including the generation of a warning signal. I

Although only one embodiment of the invention has been illustrated in the accompanying drawings and described in the foregoing specification, it is to be especially understood that various changes, such as in the relative dimensions of the parts, materials used, and the like, as well as the suggested manner of use of the apparatus of the invention may be made therein without departing from the spirit and scope of the invention will now be apparent to those skilled in the art.

What is claimed is: 1. In a gas anesthesia machine provided with a source ofox-ygen under pressure, a source of anesthetizing gas under pressure, meansfor controlling'and mixing the oxygen and anesthetizing gas, a breathing circuit for a patient, and meansfor delivering the gas-oxygen mixture to the breathing circuit, the improvement which comprises means responsive to a drop in pressure of the source of oxygen below a predetermined value to disable the means for delivering the gas-oxygen mixture to the breathing circuit thereby to shut off the flow of all gas to the breathing circuit, and means thereupon to connect the breathing circuit to a source of a further oxygen-containing gas.

2. Apparatus as claimed in claim 1, comprising signalling means which is operative to provide a warning signal when themeans for delivering the gas-oxygen mixture to thebreathing circuit is disabled.

3. In a gas anesthesia machine provided with a source of oxygen under pressure, a source of anesthetizing gas under pressure, means .for controlling and mixing the oxygen and anesthetizing gas, a breathing circuit for a patient, and. means for deliver-ing the gas-oxygen mixture to the breathing circuit, the improvement which comprises meansresponsive to adrop in pressure of the source of oxygen below a predetermined value to disable the means for delivering the gas-oxygen mixture to the breathing circuit thereby to shut 01f the flow of all gas to the breathing. circuit, means thereupon to connect the breathing circuit to a source of a further oxygen-containing gas, and means for generating a. warning signal when the means for delivering the gas-oxygen mixture to the breathing circuit is disabled.

4. In a gas anesthesia machine provided with a source of oxygen. under pressure, a source of anesthetizing gas under pressure, means for controlling and-mixing the oxygenand anesthetizing. gas, a breathing circuit for a patient, and means-for. delivering the gas-oxygen mixture to the breathing-circuit, the improvement which comprises mechanicalmeansresponsiveto adrop in pressure of the source of oxygen below a predeterminedvalue to disable the means for delivering the gas-oxygen mixture to the breathing circuit therebyytosshut off the flow of all gas to the-breathing circuit,..mechanical means. thereupon to connect thebreathingcircuit. to a. source of a further oxygen-containinggas, andrnechanical means for generating a; warning-signal whenthe means for deliveringthegas oxygen mixture to the breathing circuit is disabled.

5;: In a gas anesthesia machine provided with. a source of oxygen under pressure, a source. of anesthetizing gas under pressure, means :for. controlling and mixingthe oxygenand anesthetizinggas, a breathing circuit for a patient, and means.v for delivering,thegas-oxygenmixture to the breathing circuit, the. improvement. which comprises a multiposition .valve connected between the breathing circuit and the means for delivering thegas-oxygenmixture thereto, .saidvalve in: at first, normal position connecting the .breathingcircuit to saidmixture delivering means and in:a second positiondisconnecting the mixture delivering means. from the breathing, circuit. and. connecting the breathing-circuitto asource. of afurther oxygen-containing gas, and means responsivetoa drop in pressure. of the source oiioxygen for the machine below a. predetermined value'toshiftthe .valvefrom said first= to saidsecondposition.

6.. Apparatusas: claimed in..claim 5, comprisingmeans for generating a warning signal when the valve is-shi'fted from saidfirst to saidsecond position.v

7. Apparatus as claimedin claim 5, wherein in its secmeans to a vent.

8. Apparatus as claimed in claim 7, wherein an audible 5 gas-operated signalling device is connected to be powered by gas delivered to said vent.

9. Apparatus as claimed in claim 5, comprising a whistle, a port in the valve to which the whistle is operatively connected, said port being operatively connected to the mixture delivering means when the valve is in its second position, the port being operatively disconnected from the mixture delivering means when the valve is in the first position.

10. In a gas anesthesia machine provided with a source under pressure, means for controlling and Inixingthe oxy-' gen and anesthetizing gas, a breathing circuit for a patient,

and means for delivering the gas-oxygen mixture to the.

breathing circuit, the improvement which comprises a fluid pressure operated multiposition valve connected between the breathing circuit and the means for delivering the gasoxygen mixture thereto, said valve having a valve chamber and a movable valve element therein, said valve in a first, normal position of the movable valve element thereof con necting the breathing circuit to said mixture delivering means and in a second position of the'v-alve element disconnecting the mixture delivering means from the breathing circuit and connecting the breathing circuit to a source of a further oxygen-containing gas, a pressure operated actuator for the movable element of the valve, said actuator being connected to the valve and the source ofv oxygen for the machine, the actuator functioning to shift the valve element from its first to its second position upon a drop in the pressure of the oxygen supply of the machine below a predetermined value.

11. Apparatus as claimed in claim 10, wherein'the' valve comprises means resiliently biasing. the valve'ele'ment'toward its second position, and means cooperating, with the chamber to overcome the biasing means and to thrust the of the valve is subjected to fluid pressureat leastequal to said predetermined value, and wherein the actuator in normal operation connects the source of oxygen under pressure for the machine to the chamber of the valve, and the" actuator upon a drop in the pressure of the oxygensupplyv of the machine below said predetermined value connects" the chamber of the valve to a vent.

References Cited UNITED STATES PATENTS 3,006,339 10/1931 Smith 128-191 3,077,191 2/1963 Stanton.

FOREIGN PATENTS 966,941 3/1950 France. 579,376 6 /1933 Germany. 1,112,899 871961 Germany.

629,159 9/1949 Great Britain.

RICHARD A. GAUDET, Primary Examiner.

ROBERT E. MORGAN, Examiner.

W. E. KAMM, Assistant Examiner.

of oxygen under pressure, a source of anesthetizing gas.

valve element into its first position when the chamber

Claims

1. IN A GAS ANESTHESIA MACHINE PROVIDED WITH A SOURCE OF OXYGEN UNDER PRESSURE, A SOURCE OF ANESTHETIZING GAS UNDER PRESSURE, MEANS FOR CONTROLLING AND MIXING THE OXYGEN AND ANESTHETIZING GAS, A BREATHING CIRCUIT FOR A PATIENT, AND MEANS FOR DELIVERING THE GAS-OXYGEN MIXTURE TO THE BREATHING CIRCUIT, THE IMPROVEMENT WHICH COMPRISES MEANS RESPONSIVE TO A DROP IN PRESSURE OF THE SOURCE OF OXYGEN BELOW A PREDETERMINED VALUE TO DISABLE THE MEANS FOR DELIVERING THE GAS-OXYGEN MIXTURE TO THE BREATHING CIRCUIT THEREBY TO SHUT OFF THE FLOW OF ALL GAS TO THE BREATHING CIRCUIT, AND MEANS THEREUPON TO CONNECT THE BREATHING CIRCUIT TO A SOURCE OF A FURTHER OXYGEN-CONTAINING GAS.