GB2166360A

GB2166360A - Anaesthetic gas apparatus

Info

Publication number: GB2166360A
Application number: GB08513890A
Authority: GB
Inventors: Gerald Swann; Joaquin Martinez
Original assignee: CESTRADENT Ltd
Current assignee: CESTRADENT Ltd
Priority date: 1984-09-22
Filing date: 1985-06-03
Publication date: 1986-05-08
Also published as: GB2166360B; GB8424052D0; GB8513890D0

Abstract

A self-latching gas valve 17 suitable for use as a general anaesthesia selector in apparatus for controlling the supply of gaseous anaesthetic and oxygen to a medical or dental patient comprises a plunger 22 manually depressible against a spring bias 23 to close a passage between a gas inlet 24 and a gas outlet 26, and a latch 33 operable by gas pressure at the gas inlet to latch the plunger in the closed position, such that removal of pressure at the inlet causes the latch to release the plunger to be returned by the spring bias to the open position thereof. Where the apparatus comprises an oxygen by-pass to maintain a minimum flow of oxygen to the patient, the valve is included in the by-pass to close off the minimum supply when rapid general anaesthesia is to be achieved, the self-latching facility ensuring that, when the apparatus is used again after having been shut down, the oxygen by-pass has been re-opened by the removal of inlet oxygen pressure during the shut down period. A control valve for the vaporiser is also described and claimed, Figs 3 & 4, not shown. <IMAGE>

Description

SPECIFICATION Anaesthetic gas apparatus This invention relates to apparatus for controlling the supply of gaseous anaesthetic and oxygen to a medical or dental patient, and to a self-latching gas valve suitable for use in such apparatus.

Typically, such apparatus comprises an inlet for anaesthetic gas, for example nitrous oxide, an inlet for oxygen, an oulet for gas to be supplied tothe patient, flow metering and control means for each gas between the respective inlet and the outlet, and an oxygen by-pass for the oxygen flow control means, whereby a minimum flow of oxygen to the outlet, can be maintained irrespective of the operation of the flow control means. This arrangement ensures that the apparatus is always used for relative analgesia or sedation, for example for dental surgery. The minimum oxygen flow ensures that the patient does not become completely unconscious, with the consequent higher risk to the patient.However, in certain circumstances it is desirable to use the same apparatus for administering general anaesthetic, and this will be done with a suitably qualified person to control the supply of anaesthetic gas. For this purpose, the oxygen by-pass is provided with a simple "on-off" valve so that the oxygen flow can be completely shut off to permit the supply of pure anaesthetic gas if required by the operator to render the patient unconscious quickly. The oxygen flow is then restored using the flow control.

With this type of apparatus, often referred to as RA/GA apparatus, it is possible for the apparatus to be left with the by-pass valve closed, and it is then possible for the next person using the apparatus accidently to administer a lower percentage of oxygen to the patient than is compatible with relative analgesia.

The present invention provides a self-latching gas valve suitable, for example, for use as a general anaesthesia selector means in the oxygen bypass, the valve comprising a plunger manually depressible against a spring bias to close a passage between a gas inlet and a gas outlet, and a latch operable by gas pressure at the gas inlet to latch the plunger in the closed position, such that removal of the pressure at the inlet causes the latch to release the plunger to be returned by the spring bias to the open position thereof.Thus, when apparatus of the type hereinbefore described, and including such a valve as a general anaesthesia selector means, is being used for general anaesthesia and the gas supplies are shut down while the apparatus is left, the shutting off of oxygen pressure to the apparatus releases the latch and thereby releases the plunger so that the apparatus reverts to its relative analgesia configuration ready for next use thereof.

It is often desirable to use in conjunction with apparatus of this general type, a liquid anaesthethic vaporiser having a manual selector valve so that the gas mixture supplied to the patient can be passed direct to the patient or can be deflected through the vaporiser so as to have mixed therewith vaporised liquid anaesthitic such as fluothane.

However, a problem which can arise is that, if the operator forgets to return the manual selector valve to the by-pass position, the next patient to receive a relative analgesia from the apparatus may also be supplied with vaporised liquid anaesthitic, possibly producing undesired general anaesthesia.

Another aspect of the present invention provides apparatus for controlling the supply of gaseous anaesthetic, vaporised liquid anaesthetic, and oxygen to a medical or dental patient, the apparatus being of the general type herein before described, also comprising a vaporiser connected to the outlet for introducing vaporised liquid anaesthetic into the gas in the outlet, a first vaporiser by-pass and a manual first selector valve for opening the vaporiser and/or the first vaporiser by-pass to the flow of gas, a second vaporiser by-pass up-stream of the first vaporiser by-pass, and a second selector valve for alternatively opening the vaporiser or the second vaporiser by-pass, the second selector valve being arranged to operate in response to closure of the oxygen by-pass to open the vaporiser and to close the second vaporiser by-pass and to release in response to removal of oxygen pressure at the inlet to the apparatus.

Preferably the oxygen by-pass includes a valve having a control outlet providing a control supply of oxygen only when the valve is closed to close the oxygen by-pass, and the second selector valve comprises a piston valve drivable against a spring by the control supply of oxygen to close the second vaporiser by-pass and to open the vaporiser and/or first vaporiser by-pass to the passage of gas.

The first selector valve may comprise a rotatable body having passageways leading to and from the vaporiser and alignable with an inlet and an outlet, and the first vaporiser by-pass comprises a separate passageway through the body alignable with the inlet and outlet by rotation of the body, the passageways being arranged relative to the inlet and outlet such that rotation of the body can permit flow through the vaporiser, the by-pass or through both.

Reference is made to the drawings, in which: Figure 1 is a schematic flow diagram of conventional RA/GA apparatus; Figure 2 is a sectional view of a general anaesthesia selector for use in apparatus according to the present invention; Figure 3 is a sectional plan view of a vaporiser for use with the apparatus of the invention, the gases by-passing the vaporiser bowl; and Figure 4 is a view corresponding to Figure 3, with the gases passing through the vaporiser bowl.

Referring to Figure 1, the apparatus has oxygen and nitrous oxide inlet lines 1 and 2 respectively, the oxygen line being provided with an "on-off" switch or valve 3, downstream of which is connected a pressure dependent switch of valve 4 which closes the nitrous oxide inlet line when the pressure in the oxygen line downstream of the switch 3 drops below a predetermined value, i.e.

when the switch is closed. The nitrous oxide flows to a mixed gas outlet line 5 via a variable flow control valve 6, a maximum flow preset valve 7 and a flow meter 8. The oxygen flows to the outlet line 5 via a flow control valve 9 and a flow meter 10, but an oxygen by-pass line 11 is provided around the flow control valve 9.

The by-pass line 11 contains a maximum flow preset valve 12 and is arranged so that a minimum flow of oxygen to the outlet is preserved even when the flow control valve 9 is completely closed.

This ensures that the apparatus can induce no more than relative analgesia.

Also downstream of the "on-off" switch or valve in the oxygen line is a visual on off warning device 13 which is pressure activated and which shows whether or not the apparatus is switched on. Upstream of the on off switch 3 is a low pressure detector 14 aranged to give an audible warning when the oxygen pressure drops below a predetermined value. Finally, a direct feed 15 from the oxygen inlet 1 to the mixed gas outlet line 5 is provided via an oxygen on-off valve 16, whereby pure oxygen can be directed rapidly into the gas outlet, for example in case of an emergency.

Also provided in the oxygen by-pass line 11 is a RA/GA selector valve. This permits the by-pass to be closed, thereby permitting the flow of oxygen into the outlet to be reduced below the minimum level provided for by the by-pass. Closure of this valve 17 permits the apparatus to be used for administering general anaesthesia using a temporary delivery of pure nitrous oxide or a hgh concentration of nitrous oxide to induce rapid unconsciousness in the patient. The oxygen flow in the mixture is then restored to a controlled rate.

The selector valve 17 may be seen in more detail from Figure 2. The valve 17 has a valve body 20 provided with a central bore 21 in which a plunger 22 slides against the force of a compression spring 23. The plunger 22 extends beyond the valve body 20 so as to be manually depressible. Oxygen gas enters the valve body through an inlet 24 and passes via a screw adjuster 25 through the central bore 21 and into an oxygen outlet 26.

The plunger 22 has around the end adjacent to the spring 23 a seal 27, so that depression of the plunger seals off the passage between the oxygen inlet 24 and the oxygen outlet 26. A second seal 28 is provided at a distance along the plunger 22 to prevent escape of oxygen out of the bore 21 around the free end of the plunger 22. This provides, when the plunger is depressed a passage for oxygen from the inlet 24 to a control outlet 29, which communicates via a flexible tube 30 with a piston arrangement 31 comprising an adjustable sleeve 32 screw mounted in the valve body 20, in a bore of which slides a piston 33 which can extend into the central bore 21, but which is spring biased away therefrom by a compression spring 34 therearound.The plunger 22 has provided in a central portion thereof first and second portions of reduced diameter 35 and 36 respectively, the second portion 36 being of a smaller diameter than the first portion 35. On the opposite side of the valve body from the plunger 33 a screw mounted stop 37 extends into the bore and engages the shoulder surrounding the portion 35 of reduced diameter so as to prevent ejection of the plunger 22 by the spring 23. The piston 33 is adjusted so that, when gas passes from the inlet via the control outlet 29 to the piston arrangement 31 to drive the piston downwardly, it can engage against the shoulder between the first and second portions of reduced diameter, thus preventing release of the plunger to the rest position and thereby preventing oxygen from passing to the outlet 26.The device remains in this position until the oxygen pressure is removed from the inlet 24, i.e. by the on off switch (Figure 1) being closed, thus allowing the plunger to be released to revert to its rest position.

This ensures that, if the apparatus is left in the GA position, switching off of the gas supply causes the apparatus to revert to the RA position so that it may be used safely by the next operator.

Referring to Figures 3 and 4, the vaporiser has an inlet 40 for mixed gases from an apparatus such as hereinbefore described with reference to Figures 1 and 2, a direct oxygen inlet 41 connected to the oxygen supply, and a gas outlet 42. The vaporiser includes a bowl for receiving the liquid anaesthetic, the gases being passed over the surface of the liquid to vaporise the liquid. This part of the apparatus is conventional and will not be described in further detail.

The vaporiser block 43 includes a central gas passage 44 in which a gas selector valve 45 is located. The gas selector valve 45 is manually adjustable to deflect the gas flow from the inlet 40 through the vaporiser bowl or through a by-pass 46 in the head of the valve 45, or with a proportion of the gas flowing through each.

The direct oxygen inlet 41 is connected via a passage 47 to a direct oxygen valve 48, operation of which introduces oxygen under relatively high pressure into the outlet 42. This is used when it is necessary rapidly to give the patient a large dose of oxygen.

The block 43 also contains a vaporiser by-pass passage 49 and the gas flow is selected between the central gas passage 44 and the by-pass 49 by a gas-operated selector valve member 50, which is biased by a spring 51 to close the passage 44. The valve 50 is driven by a piston 52 at one end thereof, the head of which is exposed to a chamber 53 connected via a supply bore 54 and a flexible pipe (not shown) to, for example, the control outlet 29 of the apparatus described hereinbefore with reference to Figure 2 of the invention.

When gas pressure is present in the control outlet 29, the piston 52 drives the valve member 50 to the position shown in Figure 4, wherein the gas can pass around the valve member and into the passage 44. The operator can then select a proportion, if any, of vaporised liquid anaesthetic to be introduced into the gas, using the valve 45. It will be seen that with this arrangement, the apparatus cannot be used to deliver vaporised liquid anaesthetic unless the GA position of the apparatus de scribed with reference to Figure 2 has been selected.

Claims

1. A self-latching gas valve, comprising a plunger manually depressible against a spring bias to close a passage between a gas inlet and a gas outlet, and a latch operable by gas pressure at the gas inlet to latch the plunger in the closed position, such that removal of pressure at the inlet causes the latch to release the plunger to be returned by the spring bias to the open position thereof.

2. A valve according to Claim 1, wherein gas is supplied from the inlet to operate the latch only when the plunger is in the closed position.

3. A valve according to Claim 1 or 2, wherein the latch comprises a piston spring-biased away from the plunger and movable by gas-pressure into engagement with a shoulder on the plunger.

4. Apparatus for controlling the supply of gaseous anaesthetic and oxygen to a medical or dental patient, the apparatus comprising an inlet for anaesthetic gas, an inlet for oxygen, an outlet for gas to be supplied to the patient, flow metering and control means for each gas between the respective inlet and the outlet, an oxygen by-pass for the oxygen control means, whereby a minimum flow of oxygen to the outlet can be maintained irrespective of the operation of the flow control means, and a general anaesthetic selector means in the oxygen by-pass, the selector means comrising a self-latching gas valve according to Claim 1, 2 or 3.

5. Apparatus for controlling the supply of gaseous anaesthetic and oxygen to a medical or dental patient, substantially as described with reference to Figures 1 and 2 of the drawings.

6. Apparatus for controlling the supply of gaseous anaesthetic, vaporised liquid anaesthetic, and oxygen to a medical or dental patient, the apparatus comprising an inlet for oxygen, an inlet for anaesthetic gas, an outlet for gas to be supplied to the patient, flow metering and control means fo each gas between the respective inlet and the outlet, an oxygen by-pass for the oxygen flow control means, whereby a minimum flow of oxygen to the outlet can be maintained irrespective of the operation of the flow control means, a vaporiser connected to the outlet for introducing vaporised liquid anaesthetic into the gas in the outlet, a first vaporiser by-pass and a manual first selector valve for opening the vaporiser and/or the first vaporiser by-pass to the flow of gas, a second vaporiser bypass upstream of the first vaporiser by-pass, and a second selector valve for alternatively opening the vaporiser or the second vaporiser by-pass, the second selector valve being arranged to operate in response to closure of the oxygen by-pass to open the vaporiser and to close the second vaporiser bypass and to release in response to removal of oxygen pressure at the inlet to the apparatus.

7. Apparatus according to Claim 6, wherein the oxygen by-pass includes a valve having a control outlet providing a control supply of oxygen only when the valve is closed to close the oxygen by pass, and the second selector valve comprises a piston valve drivable against a spring by the con trol supply of oxygen to close the second vaporiser by-pass and to open the vaporiser and/or first vaporiser by-pass to the passage of gas.

8. Apparatus according to Claim 6 or 7, wherein the first selector valve comprises a rotatable body having passageways leading to and from the vaporiser and alignable with an inlet and an outlet, and the first vaporiser by-pass comprises a separate passageway through the body alignable with the inlet and outlet by rotation of the body, the passageways being arranged relative to the inlet and outlet such that rotation of the body can permit flow through the vaporiser, the by-pass or through both.

9. Apparatus for controlling the supply of gaseous anaesthetic, vaporised liquid anaesthetic, and oxygen to a medical or dental patient, substantially as described with reference to, or as shown in, Figures 3 and 4 of the drawings.