GB2062475A

GB2062475A - Respiratory apparatus

Info

Publication number: GB2062475A
Application number: GB8035697A
Authority: GB
Original assignee: Draegerwerk AG and Co KGaA
Current assignee: Draegerwerk AG and Co KGaA
Priority date: 1979-11-10
Filing date: 1980-11-06
Publication date: 1981-05-28
Also published as: DE2945472A1; DE2945472C2; SE8306045L; SE455166B; GB2062475B; SE443722B; SE8306045D0; SE8006238L

Abstract

An apparatus for supplying respiratory gas to a patient has a first variable volume chamber or bellows (1) connected to a respiratory gas circuit (A) which supplies gas via a facepiece to a patient (15). A respiratory gas (pref. a mixture of O2 and N2O which may contain additional anaesthetic from a vaporiser (22)), is supplied from a respiratory gas preparation device (B). A pneumatic control device (C) has a control unit (3, 9), for controlling the pressure in an inner housing (11) which houses the bellows (1), and which controls the supply of respiratory gas from the bellows (1) to the patient (15). A second, manually operable variable volume chamber (24) can be connected to the respiratory gas circuit (A) instead of the first chamber so that respiration can be effected manually. The bellows (1) are interchangeable so that a bellows having a volume corresponding to the volume of the patient's lungs can be selected. <IMAGE>

Description

SPECIFICATION Respiratory apparatus This invention relates to respiratory apparatus, and more particularly, but not exclusively, is concerned with respiratory apparatus which includes a pneumatically operated control unit.

Respiratory apparatus, for gases containing anaesthetic, which include pneumatic control can overcome the danger of explosion which many anaesthetics possess. Basically such respiratory apparatus should be leak-proof; excess exhalation gases which may contain anaesthetic should be collected and removed. The flow rate of artificial respiration gas should be adjustable for both adults and children without risk to these patients. Simple disinfection of all apparatus parts which come into contact with the respiratory air should be possible.

A Aknown artificial respiratory apparatus described in British Patent Specification 1,096,030 permits the artificial respiration of the patient both in an open and in a closed circulation system. As well as the valves necessaryforthe appropriate air supplies, it contains respiratory bags disposed in containers which are alternately placed under over- or underpressure, relative to atmospheric pressure. Inhalation and exhalation are controlled by an apparatus generating the over- and under-pressure. For disinfection all parts which come into contact with the respiratory air are seprated from the apparatus generating the pressures. The artificial respiration apparatus is complicated by the control required for the over- and under-pressures.Adaptation of the flow parameters to a particular patient is very difficult. Artificial respiration by hand after failure of the pressure generating apparatus is impossible.

A further known pneumatically controlled artificial respiratory apparatus, more particularly an anaesthetic apparatus, is disclosed in German Offenlegungsschrift 25 54674 and permits automatic operation and the changeover to manual operation.

The automatic operation, during which the respiratory air is forcibly circulated, is essentially effected via bellows in a housing in which said bellows are acted upon from outside with pressure. By longitudinal displacement of the bellows, it is possible to alter the circulation volume. The changeover from automatic to manual operation is made by the displacement of an adjusting rod in a changeover valve.

With the displacement the automatic supply apparatus to the patient is cut off and a connection between the patient and a bag compressible by hand is established. From this bag, by means of compression, the respiratory air is then conveyed to the patient. It returns to the manual bag by exhalation. In the "manual operation" position spontaneous breathing by the patient is possible. There is no automatic switchoverto "manual operation", e.g. after failure of the automatic artificial respiration, possibly caused by lack of pressurised gas. The necessary disinfection process is not described. With the many apparatus parts it would be difficult to effect. Adaptation of the respiratory volume to adults and children requires special care.

According to the present invention there is provided a respiratory apparatus, for supplying respiratory gas to a patient, comprising: an inner housing; an interchangeable first variable volume chamber which is disposed in the inner housing; an other housing in which the first variable volume chamber and the inner housing are removably disposed, the outer housing in use urging the first variable volume chamber against the inner housing to close and seal the inner housing; a respiratory gas circuit, for supplying respiratory gas to a face piece for a patient, which circuit is in communication with the first variable volume chamber; a control unit for controlling the pressure in the inner housing and hence the supply of respiratory gas from the first variable volume chamber via the respiratory gas cir cuittothefacepiece; and a second, manually operable variable volume chamber which is in communication with the respiratory gas circuit and, in use, can be used, instead of the first variable volume chamber, to control the supply of respiratory gas to the face piece.

The first variable volume chamber can comprise bellows which are displaceable along an axis of the bellows, and the second variable volume chamber can comprise a resilient bag.

The control unit can comprise a pneumatic control unit, and can include a pressurised gas control device which comprises: an inlet for connection to a source of pressurised gas; an outlet connected to the inner housing; a first flow regulating valve and a first control valve disposed in series between the inlet and the outlet; a throttle connected between the inlet and the outlet, parallel to the first flow regulating valve and the first control valve; and a control line connected between the inner housing and the first control valve, the arrangement being such that, in use, the first control valve is open when the pressure in the inner housing is below a predetermined value but closed when that pressure exceeds that predetermined value.

Preferably the outlet of the pressurised gas control device is connected to the inner housing via a second control valve; the inner housing is connected by a third control valve to a discharge line which opens into the atmosphere; and the control unit includes a respiratory control device which has an inlet for pressurised gas and is connected to, and controls, the second and third control valves; the arrangement being such that, in use, the second control valve is open and the third control valve closed during an inhalation phase so that pressurised gas is supplied via the pressurised gas control unit to the inner housing compress the bellows, and during an exhalation phase the second control valve is closed and the third control valve is open to permit gas in the inner housing to discharge to the atmosphere and the bellows to expand and refill with gas.

Preferably the first variable volume chamber opens into a gas line, one end of which communicates via a fourth control valve and a non-return valve with the atmosphere, the non-return valve only permitting gas to flow from the gas line to atmosphere, and the fourth control valve is controlled by the respiratory control device, the fourth control valve being closed during an inhaiatiorl phase and open during an exhalation phase. ?-#uen#agaously, the other end of the gas line is conne#:#d to a changeover valve which has an inlet and outlet port connected to the respirator1 gas circuit and which is connected to the second variable volume chamber and to the respiratory control device; the arrangement being such that, provided the respiratory control device supplies gas at a pressure greater than a second predetermined value, then the changeover valve connects the respiratory gas circuit to the gas line, but if the pressure of the gas supplied by the respiratory control device is less than the second predetermined value, then the respiratory gas circuit is connected to the second variable volume chamber.

The interchangeable bellows enables the apparatus to be adapted to the needs of adults or children. Also, the interchangeable bellows can include a mounting member provided with a gas duct. The bellows and associated components, a so-called "patient system can be readily changed and sterilised. The provision of a changeover valve enables the apparatus to be simply switched from automatic to manual operation.

A preferred embodiment of the present invention includes the interchangeable bellows or patient system, a pressurised gas control device and a changeover valve. The combination of these components provides an easy to use anaesthetic artificial respiratory apparatus. The patient system comprises the bellows determining the respiratory volume, and it can include a handle to facilitate its removal from the housing. The bellows are interchangeable so that bellow sizes for adults or children can be used. The parts of the patient system which come into contact with the exhalation air are accessible for disinfection at the same time.

The facility for easily exchanging the bellows and the accessibility for disinfection can be of advantage, as it appears again and again that in routine operation operational faults and faults caused by neglect otherwise easily occur.

The pressure gas quantity control device can ensure a low pressurised gas consumption in the circulatory supply of the respiratory gas. The compression of the bellows and thereby the expulsion of the respiratory gas to the patient is performed during a first stage of the inhalation phase. Following this as a further stage is a pause in which the bellows are held compressed and the supplied respiratory gas can distribute in the lungs. During this pause the first control valve which lets through most of the pressurised gas is closed. Only a small amount of pressurised gas then flows through the fixed throttle in order to hold the bellows compressed. This can reduce the amount of noise generated.

An advantage of an automatic changeover valve lies in the fact that in the event of failure of the pneumatic system and the resulting loss of pressure in the line for pneumatic control, it immediately switches over automatically to manual artificial respiration. This takes care of an essential safety aspect.

For a better understanding of the present inven tilan and to show more clearly how the same may be carried into effect, reference will now be made, by way of example, to the accompanying dralJings in which: Figure 1 shows diagrammatically a respiratory apparatus, according to the present invention; Figure 2 shows the bellows and housing of the respiratory apparatus of Figure 1; Figure 3 shows a partial section through an alternative embodiment of the bellows; Figure 4 shows diagrammatically the pressurised gas control device of the respiratory apparatus; and Figure 5 shows a section through the changeover valve and the second variable volume chamber of the respiratory apparatus.

The respiratory apparatus can be subdivided into 3 main components. Component A comprises a respiratory gas circuit which supplies respiratory gas to a patient. Component B comprises a device for the preparation of a respiratory gas containing an anaesthetic, and Component C comprises a pneumatic control unit for controlling respiration.

The respiratory gas circuit includes a main respiratory gas line 50 which is connected by a pressure limiting valve 16, which limits the maximum pressure attainable in the respiratory gas circuit, to an anaesthetic gas exhaust 17. A respiratory mask or facepiece, not shown, is connected by an inhalation non-return valve 14 and a carbon dioxide absorber 13 and also by an exhalation non-return valve 18 and a respiratory gas volume meter 19 to the main respiratory gas line 50. The line 50 is supplied with oxygen and nitrous oxide from inlets 70 and 71 which are connected to the line 50 via flow meters 21 and a vaporiser 22, in which an additional anaesthetic can be added to the gas mixture. The respiratory gas pressure can be monitored via a pressure gauge 20 connected to the line 50, and the volume of exhaled gas is measured by the volume meter 19.

A first variable volume chamber or bellows 1 is disposed in an inner housing 11, and the maximum volume of the bellows 1, when expanded, is limited by an adjustable stop 2, which can thereby set a respiration volume Vt. The pneumatic control unit includes a respiratory control device 3 for controlling respiration and a pressurised gas control device 9.

The respiratory control device 3 includes a means 4 for controlling the respiratory frequency and a means 5 for controlling the Post Exhalation Excess Pressure (PEEP). An inlet 60 for pressurised control gas is connected via a pressure reducer 10 to the pressurised gas control device 9, which includes a first control valve 44 (see Figure 4) and which is connected via a second control valve 8 to the housing 11.

The pressure reducer 10 also supplies gas to the respiratory control device 3. The housing 11 communicates with the atmosphere via a third control valve 7 and a silencer or damper 12. The gas line 49 includes a fourth control valve 6 and a non-return valve 23 which permits gas to flow only from the line 49 to atmosphere. The first control valve 44 is connected by a control line 43 to the housing 11 so that the valve 44 is controlled in dependence upon the pressure in the housing 11. The second, third and fourth control valves 8,7 and 6 are connected to and controlled by the respiratory control device 3. The gas line 49 is connected by the changeover valve 25 to the main respiratory gas supply line 50. For control purposes the changeover valve 25 is connected to the respiratory control device 3 by a further control line 45, which includes another control valve or switch 26.

The flow rate of pressurised gas can be set by the pressurised gas control device 9, and, in accordance with the set flow rate, gas, during an inhalation phase, flows into the housing 11 and compresses the bellows 1. The respiratory gas in the bellows 1 is expelled and flows via the changeover valve 25, the main respiratory gas line 50, the CO2 absorber 13 and the inhalation non-return valve 14 to a patient 15, whose lungs are shown symbolically. During an inhalation phase, the first and second control valves 44 and 8 are open and the third control valve 7 is closed so that the pressurised gas has to flow into the housing 11. Simultaneouslythe fourth control valve 6 is closed so that the respiratory gas from the bellows 1 cannot flow outto atmosphere.

At the end of the inhalation phase, an exhalation phase commences. The second control valve 8 is closed and the third control valve 7, which is a venting valve, is opened so that the housing 11 can vent to atmosphere via the silencer 12. Simultaneously, the fourth control valve 6 is opened so thatthe patient 15 can exhale to the atmosphere. As the housing 11 is vented to the atmosphere, the bellows 1 are able to expand again and thus the pressure in the respiratory gas circuit falls and the patient 15 is able to exhale via the exhalation non-return valve 18.

As the bellows 1 are expanding during the exhalation phase fresh respiratory gas containing anaesthetic as well as the patient's exhaled gas pass into the bellows 1. The fresh respiratory gas may be a mixture of oxygen (02) and nitrous oxide gas (N2O), which can include an additional anaesthetic. The surplus gas is discharged via the exhalation valve 6 and the lightly spring-loaded non-return valve 23 to an anaesthetic gas exhaust 17.

Control of the valves 6, 7 and 8 and hence the timing at the inhalation and exhalation phases is effected by the respiratory control devices 3, in dependence upon the setting of the means 4 for controlling the respiratory frequency.

As is described below, the changeover valve 25 is controlled in dependence upon the pressure in the control line 45. The main respiratory gas line 50 can be connected with to the gas line 49 orto the manual bag 24. When the line 50 is connected to the manual bag 24, respiration is effected by manual operation of the bag 24 in the known manner.

Reference will now be made to the details of the bellows 1 and the housing 22 shown in Figure 2. A comparatively small bellows 1 for artificial respiration of children is shown, but it can be exchanged for a a larger bellows 1 for artificial respiration of adults.

The bellows 1, a portion of the gas line 49 integral therewith, and a wedge 35 are referred to as a patient circuit 33. When changing the bellows 1, it is the patient circuit 33 which is exchanged.

The housing 11 can be pressurised. The adjustable stop 2 comprises a support plate 31 which is slidably mounted on rods 61 by means of guides 32. A threaded nut or bore 30 of the support plate 31 engages a threaded shaft 28 mounted in bearings 29.

The threaded shaft 28 is driven via a pair of gears 27 by a horizontal shaft 62 which has a knob at its left hand end. Hence the maximum vertical displacement of the bellows can be adjusted by rotation of the shaft 62, to adjust the maximum volume ofthe bellows 1. When fully expanded a lower end of the bellows 1 abuts the support plate 31.

The interior of the patient circuit 33 is sealed off from the interior of the housing 11 by a seal 34, and the seal 34 is compressed by the wedge 35. The wedge 35 also abuts a roller bearing 36 which is secured to an outer housing 37, and holds the patient circuit 33 in position.

In orderto exchange the patient circuit 33, the patient circuit 33, the housing 11 and all the components of the adjustabie stop 2 are slid out from the outer housing 37. The original patient circuit 33 is then exchanged for another patient circuit 33 which is located in the housing 11. The housing 11 and the new patient circuit 33 are then slid into the outer housing 37, and the roller bearing 36 acting on the wedge 35 of the new patient circuit 37 urges the patient circuit 33 against the seal 34 to seal the housing 11.

Figure 3 shows a patient circuit 33 with a large bellows 1 for adult artificial respiration and with a respiratory gas duct 54 which is connected to the gas line 49 by the connector 55. The other end of the gas duct 54, the right hand end in Figure 3, does not need to be connected to the gas line 49 as it includes the components in the right hand end of the gas line 49 shown in Figure 1, namely the fourth control or exhalation valve 6 and the non-return valve 23. The control valve 6 is a diaphragm valve which is controlled by pressurised gas supplied through a line 39 from the respiratory control device 3. This embodiment of the patient circuit 33 has a handle 38, and with the housing 11 it may be slid into position in the outer housing 37.

The pressurised gas control device 9 has a flow regulating valve 40 and the first control valve 44 connected in series between an inlet connected to the pressure reducer 10 and an outlet connected to the second control valve 8. A throttle 41 is arranged in parallel to the valves 40 and 44. An actuating unit 42 for the valve 44 includes a pressure monitor which monitors the pressure in the housing 11 via the line 43 and controls the first control valve 44 in dependence upon the monitored pressure.

The actuating unit 42 with the pressure monitor controls the valve 44 so that when there is a pressure in the housing 11 between 0 and 80 mbarthe valve 44 is open, but if the pressure exceeds 80 mbarthen the actuating unit 42 closes the valve 44. The pressure above 80 mbar obtains in the housing 11 when the bellows 1 are compressed after the first stage of an inhalation phase. Since a further supply of pressurised gas to the housing 11 would have no effect on the respiratory gas pressure in the bellows 1, the valve 44 is closed, and only a partial flow of about 3 1/min via the fixed throttle 41 holds the bellows 1 compressed in the next portion of the inhalation phase.When the inhalation phase is finished, the second control valve 8 is closed again and the third control valve 7 opens, so that the gas escapes from the housing 11 via the silencer 12.

Thus, the pressurised gas control device controls the flow of gas to the housing 11 during an inhalation phase. This flow of gas comprises a main flow V through the valves 40 and 44 and a partial flow through the throttle 41. Both flows are supplied during the first portion of an inhalation phase until the pressure in the housing 11 reaches 80 mbar, whereupon only the partial flow through the throttle 41 is provided.

Referring to Figure 5, the changeover valve 25 comprises two diaphragm valves 47 and 48, whose respective diaphragms 46 and 65 are interconnected by a shaft 53. The main respiratory gas line 50 is connected to a port 66, which is connected by the diaphragm valve 48 and a connector 57 to the gas line 49 and by the other diaphragm valve 47 and a connector 52 to the manual bag 24. The diaphragm 65 is acted upon by a spring 51 which closes the diaphragm valve 48 and opens the diaphragm valve 47, as shown. A chamber 56 is connected to the control line 45 so that gas under a super-atmospheric pressure can be introduced into the chamber 56 to close the valve 47 and open the valve 48 against the action of the spring 51.

In automatic artificial respiration operation, the switch 26 is closed, and ia line 45 pressurised gas acts on the diaphragm 46 to close the valve 47 and open the valve 48. Thus, the gas line 49, connected to the bellows 1, is thereby connected via the main respiratory gas line 50 to component A. In manual artificial respiration, the switch 26 is opened and thus the control line 45 and the chamber 56 are at atmospheric pressure. The spring 51 displaces the diaphragm valves 47 and 48 so that the valve 48 is closed and the valve 47 open to connect the main respiratory gas line 50 to the manual bag 24. The patient 15 can then be given artificial respiration manually by for example the doctor.

In the possible event of a breakdown of the respiratory control device 3 and the resultant failure of the automatic respiratory apparatus, the line 45 assumes atmospheric pressure. As a result the changeover valve 25 immediately switches automatically on to manual artificial respiration by the manual bag 24.

Claims

1. A respiratory apparatus, for supplying respiratory gas to a patient, comprising: an inner housing; an interchangeable first variable volume chamber which isdisposed in the inner housing; an outer housing in which the first variable volume chamber and the inner housing are removably disposed, the outer housing in use urging the first variable volume chamber against the inner housing to close and seal the inner housing; a respiratory gas circuit, for supplying respiratory gas to a facepiece for a patient, which circuit is in communication with the first variable volume chamber; a control unit for controlling the pressure in the inner housing and hence the supply of respiratory gas from the first variable volume chamber via the respiratory gas cir cuitto the facepiece; and a second, manually operable variable volume chamber which is in communication with the respiratory gas circuit and, in use, can be used, instead of the first variable volume chamber, to control the supply of respiratory gas to the facepiece.

2. A respiratory apparatus as claimed in claim 1, in which the second variable volume chamber comprises a resilient bag.

3. A respiratory apparatus as claimed in claim 1 or 2, in which the first variable volume chamber comprises bellows which are displaceable along an axis of the bellows.

4. A respiratory apparatus as claimed in claim 3, in which the inner housing is provided with an adjustable stop for limiting the expansion of the bellows.

5. A respiratory apparatus as claimed in claim 4, wherein the adjustable stop comprises a plate which is slidably mounted on one or more rods which are parallel to the axis of the bellows and wherein the position of the plate can be adjusted by rotation of a threaded shaft which engages a corresponding threaded bore in the plate.

6. A respiratory apparatus as claimed in claim 3, 4 or 5, wherein the bellows are attached to a mounting memberwhich, in use, is mounted in the inner housing, and wherein the bellows, the mounting member and the inner housing are removably disposed in the outer housing which urges the mounting member against a seal to seal the respiratory gas circuit from the interior of the inner housing.

7. A respiratory apparatus as claimed in claim 6, wherein the mounting member is integral with a wedge which is wedged between the outer housing and the mounting member.

8. A respiratory apparatus as claimed in claim 7, in which the wedge has inclined plane surfaces and is wedged between the mounting member and one or more roller bearings secured to the outer housing.

9. A respiratory apparatus as claimed in claim 6, 7 or 8, in which the mounting member includes a gas duct into which the bellows open and which is in communication with the respiratory gas circuit.

10. A respiratory apparatus as claimed in claim 6, 7, 8 or 9, wherein the mounting member is provided with a handle.

11. A respiratory apparatus as claimed in any preceding claim, wherein the control unit comprises a pneumatic control unit.

12. A respiratory apparatus as claimed in claim 11, wherein the control unit includes a pressurised gas control device which comprises: an inlet for connection to a source of pressurised gas; an outlet connected to the inner housing; a first flow regulating valve and a first control valve disposed in series between the inlet and the outlet; a throttle connected between the inlet and the outlet, parallel to the first flow regulating valve and the first control valve; and a control line connected between the inner housing and the first control valve; the arrangement being such that, in use, the first control valve is open when the pressure in the inner housing is below a predetermined value but closed when that pressure exceeds that predetermined value.

13. A respiratory apparatus as claimed in claim 12, wherein the outlet of the pressurised gas control device is connected to the inner housing via a second control valve, and the inner housing is con nected by a third control valve to a discharge line which opens into the atmosphere, and wherein the control unit includes a respiratory control device which has an inlet for pressurised gas and is con nected to, and controls, the second and third control valves; the arrangement being such that, in use, the second control valve is open and the third control valve closed during an inhalation phase so that pressurised gas is supplied via the pressurised gas control unit to the inner housing to compress the bellows, and during an exhalation phase the second control valve is closed and the third control valve is open to permit gas in the inner housing to discharge to the atmosphere and the bellows to expand and refill with gas.

14. A respiratory apparatus as claimed in claim 13, wherein the first variable volume chamber opens into a gas line, one end of which communicates via a fourth control valve and a non-return valve with the atmosphere, the non-return valve only permitting gas to flow from the gas line to the atmosphere, and wherein the fourth control valve is controlled by the respiratory control device, the fourth control valve being closed during an inhalation phase and open during an exhalation phase.

15. A respiratory apparatus as claimed in claim 14, when appendantto claim 9, with the gas duct forming part of the gas line, wherein the fourth control valve and the non-return valve are provided in one end region of the gas duct.

16. A respiratory apparatus as claimed in claim 14 or 15, wherein the other end of the gas line is connected to a changeover valve which has an inlet and outlet port connected to the respiratory gas circuit and which is connected to the second variable volume chamber and to the respiratory control device; the arrangement being such that, provided the respiratory control device supplies gas at a pressure greater than a second predetermined value, then the changeover valve connects the respiratory gas circuit to the gas line, but if the pressure of the gas supplied by the respiratory control device is less than the second predetermined value, then the respiratory gas circuit is connected to the second variable volume chamber.

17. A respiratory apparatus as claimed in claim 16, wherein the changeover valve comprises two, coupled diaphragm valves, which are arranged so that the port can communicate via one diaphragm valve with the first variable volume chamber, or via the other diaphragm valve with the second variable volume chamber, and spring means acting on the diaphragm valves to close said one diaphragm valve and to open said other diaphragm valve, the changeover valve being such that one or both of the diaphragm valves is subjected to the pressure of gas from the respiratory control device which acts against the spring means to open said one diaphragm valve if that pressure is greater than the second predetermined value.

18. A respiratory apparatus as claimed in claim 16 or 17, wherein the changeover valve is connected to the respiratory control device via a fifth control valve or switch.

19. A respiratory apparatus as claimed in any one of claims 13 to 18, wherein the respiratory control device includes means for adjusting the respiratory frequency and means for adjusting the Post Exhalation Exess Pressure.

20. A respiratory apparatus as claimed in any preceding claim, wherein the respiratory gas circuit includes a main respiratory gas supply line which is supplied with respiratory gas, is connected by a carbon dioxide absorber and an inhalation non-return valve in series to the facepiece, and by a respiratory gas volume meter and an exhalation non-return valve in series, and in parallel to the carbon dioxide absorber and the inhalation non-return valve, to the facepiece, and is connected to a pressure-limiting valve, which limits the maximum pressure in the main respiratory gas supply line, and to the first variable volume chamber, the main respiratory gas supply line also being connected to the port of the changeover valve if present, so that, in use, during an inhalation phase respiratory gas can flow from the first variable volume chamber through the main respiratory gas supply line, the carbon dioxide absorber, the inhalation non-return valve and the facepiece to a patient and, during an exhalation phase, exhaled gas from the patient can flow through the exhalation non-return valve and the respiratory gas volume meter to the main respiratory gas supply line and then to the atmosphere.

21. A respiratory apparatus as claimed in claim 20, wherein the respiratory apparatus includes an inlet for oxygen and an inlet for nitrous oxide, each of which inlets is connected via a control valve and a flow meter to a vaporiser, in which an additional anaesthetic can be added to the respiratory gas comprising oxygen and nitrous oxide, and the vaporiser is connected to the main respiratory gas line.

27. A respiratory apparatus substantially as hereinbefore described with reference to, and as shown in Figures 1,2,4 and 5 or Figures 1,2,4 and 5 when modified in accordance with Figure 3, of the accompanying drawings.