GB2076676A

GB2076676A - Gas mixing apparatus

Info

Publication number: GB2076676A
Application number: GB8110203A
Authority: GB
Original assignee: Draegerwerk AG and Co KGaA
Current assignee: Draegerwerk AG and Co KGaA
Priority date: 1980-05-28
Filing date: 1981-04-01
Publication date: 1981-12-09
Also published as: SE435572B; GB2076676B; SE8101149L; DE3020204C2; DE3020204A1

Abstract

First, second and third lines (1, 2, 3), for, for example, oxygen, air and an anaesthetic gas respectively, are connected to a common mixed gas outlet line (10). A first valve (11) and a second valve (12) are provided in the second and third lines (2, 3) respectively. The valves (11, 12) are connected to, and controlled by the pressure in, the first line (1). With an adequate pressure in the first line (1), the first valve (11) is closed and the second valve (12) is open. However, should the pressure in the first line (1) fall to or below a predetermined pressure, the first valve (11) is opened and the second valve (12) is closed. This can prevent anaesthetic gas alone being supplied (through the third line (3)), to the outlet line (10) in the event of a failure in the oxygen supply through the first line (1). <IMAGE>

Description

SPECIFICATION Gas mixing apparatus This invention relates to a gas mixing apparatus and it more particularly relates to an anaesthetic gas mixing apparatus for mixing gases for ventilators or anaesthesia apparatus.

known anaesthesia apparatus have gas mixing devices or apparatus with metering arrangements for supplying the patients with the respiratory gases as either an oxygen/anaesthetic gas mixture or an oxygen/air mixture. The safety of the patients is naturally an essential factor when designing these devices. They must make erroneous connections to other gas mixtures impossible; in the event of loss of oxygen, the anaesthetic gas must be shut off every time. In cases of emergency it must also be possible to supply the patient with ambient air alone.

A known anaesthesia apparatus, disclosed in U.S. Patent Specification 3,351,057, has a safety arrangement which is provided with sources of oxygen and anaesthetic gas under pressure. It comprises devices for mixing the oxygen with the anaesthetic gas and also for supplying the anaesthetic gas/oxygen mixture into the respiratory circuit connected to the patient. In the event of a drop in pressure in the oxygen source to below a pre-determined ,inevalue, the supply of anaesthetic gas mixture is discontinued, and the respiratory circuit is connected immediately to a source of a further gas containing oxygen, such as ambient air. In each case, after loss of oxygen, the patient does not thereby receive any more anaesthetic gas, but only air from the ambient atmosphere.Switching-over takes place by way of pressure control in purely mechanical, not electrical, manner in order to prevent ignition sources igniting any explosive gas mixtures which might possibly occur. The switching is effected by means of a pneumatic limiting pressure switch controlled by the pressure of the oxygen gas mixture portion by way of a change-over switch, likewise pneumatic, which is bistable and switches directly from one end position to the other. The safety arrangement comprises the pneumatic change-over switch, which is connected into the gas mixture line, through which, in the switched-through state, the gas mixture flows on to the patient. In the switchedover state the line to the patient is connected with the atmosphere; the gas mixture line, however, is then switched off.

Switching-over takes place by the limiting pressure switch. This is connected to the line with the oxygen gas mixture portion from the oxygen supply. The pressure prevailing therein switches the limiting pressure switch.

Either this pressure, communicated via a line, acts on the change-over switch whereby the latter provides communication between the portions of the gas mixture line, or, when the lower limiting pressure is reached, the limiting pressure switch switches, whereby the pressure then no longer acts on the change-over switch. As stated above, the change-over switch then shuts off the anaesthetic gas/oxygen mixture to the patient. In place of this, a connection thereto, i.e. a portion of the gas mixture line, is connected to the ambient atmosphere.

There is the disadvantage that it is not possible with this anaesthesia apparatus also to provide the patients with an oxygen/air mixture as might be advantageous for particular situations for the patients.

Another known gas mixing apparatus, disclosed in German Patent Application P29 26766.1, provides switchable pre-selected concentrations, more particularly for respiratory and medical apparatus. A first gas is supplied directly to one inlet of a gas mixer provided with two inlets. A solenoid valve is connected in series with the other inlet, by way of which a second or third gas can alternatively be supplied. The solenoid valve can be controlled by hand or by way of a time switch. In one position of the solenoid valve the gas mixing device supplies a mixture consisting of the 1 st and 2nd gases. In the other position a mixture of the 1 st and 3rd gases is provided.

It is true that it is impossible to mix the 2nd and 3rd gases in error. They can be mixed with the directly supplied 1 st gas only separately from one another. There is, however, the disadvantage that when oxygen is supplied directly as 1 st gas, there is no guarantee, as is desirable in such a gas mixing apparatus, that with loss of oxygen neither is there any flow of anaesthetic gas. Moreover, in terms of switching techniques, there is no provision for the air alone then to continue to flow.

What is desirable is a gas mixing device for anaesthesia apparatus with safety arrangement for oxygen, air and anaesthetic gas, with which oxygen/air of oxygen/anaesthetic gas mixtures can alternatively be produced without erroneous connections and which ensures in this respect that in the event of loss of the oxygen supply the anaesthetic gas is shut off, a supply with air alone, however, being still possible.

According to the present invention there is provided a gas mixing apparatus comprising: first, second and third gas inlet lines; a mixed gas outlet line to which the first, second and third inlet lines are connected; a first valve disposed in the second line; and a second valve disposed in the third line; wherein the first and second valves are connected to, and actuatable by the pressure in, the first line; and wherein the arrangement is such that, in use, the first valve is closed and the second valve is opened when the pressure in the first line exceeds a predetermined pressure, and the first valve is opened and the second valve is closed when the pressure in the first line falls to or below that predetermined pressure.

Preferably, the first and second valves are pneumatically actuated and are connected to the first line via a control line. The control line preferably includes a manually actuatable control valve.

Each of the first, second and third lines conveniently includes a flow-metering device for regulating and monitoring the flow in the respective line.

Each of the first and second valves, in addition to being actuatable by the pressure in the first line, can be actuated by one or more other means.

The apparatus can be, or can form part of, an anaesthetic gas mixing apparatus, with the first, second and third lines, in use, being supplied with oxygen, air and an anaesthetic gas respectively.

The first and second valves, for air and anaesthetic, provide an essential operational safety and safeguard against erroneous connections. The first valve is opened in the event of absence of a control pressure and the second valve is closed. When a control pressure is present in the oxygen supply line, all the desired requirements are met. Only one gas mixture, either oxygen/anaesthetic gas or oxygen/air can ever be formed; in the event of loss of oxygen, the first and second valves are not subject to a control pressure. No anaesthetic gas is then able to flow.

Air can then always flow for the supply, perhaps necessary for life, to the patient.

For a better understanding of the present invention and to show more clearly how the same may be carried into effect, reference wilt now be made, by way of example, to the accompanying drawing which shows diagrammatically a gas mixing apparatus according to the present invention.

The gas mixing apparatus is arranged to mix oxygen and laughing gas (nitrous oxide) as an anaesthetic gas, or oxygen and air. The gases to be mixed are supplied through a supply line 1 for oxygen, a supply line 2 for air and a supply line 3 for anaesthetic gas. The gases to be mixed flow from the central supply unit or from bottled supplied preferably reduced to a pressure of 5 bar.

Metering or each gas supply is effected by way of a control valve 4 for oxygen, a control valve 5 for air and a control valve 6 for anaesthetic gas. Also flow-metering tubes 7, 8 and 9 are provided downstream of the valves 4, 5 and 6 respectively so that the flow rates of the three gases can be monitored. Outlets of the three flow-metering tubes 7, 8 and 9 are connected to a common mixed gas line 10 which is connected to an anaesthetic apparatus or ventilator.

In the air supply line 2 upstream of the control valve 5, there is a pneumatically controlled air shutoff valve 1 which is closed when acted upon by a sufficient superatmospheric pressure. A corresponding anaesthetic gas shutoff valve 12, which is opened when acted upon by a sufficient superatmospheric pressure, is disposed in the anaesthetic gas supply line 3. The control pressure supplied to these two valves 1 1, 12, is adjusted by way of a hand valve 13 in a control pressure line 14 connected to the oxygen supply line 1.

With the hand valve 13 open - anaesthetic gas selection position - and a normal oxygen pressure obtaining in the line 1 , the anaesthetic gas shutoff valve 12 is opened and the air shutoff valve 11 is closed. The nitrous oxide can then be metered and mixed with the oxygen. With the hand valve 13 closed - air selection position~ the air shutoff valve 1 1 is opened so that air can be metered together with the oxygen and the anaesthetic shutoff valve 12 is closed.

When the hand valve 13 is open and the oxygen pressure falls, the anaesthetic gas shutoff valve 12 closes and the air shutoff valve 1 1 opens, so that the supply of anaesthetic gas is shutoff and air is supplied instead. As the oxygen pressure has fallen, air alone or an oxygen/air mixture is then supplied. It is thus ensured that there can never be any flow of nitrous oxide without oxygen being present. If oxygen supply is renewed and the oxygen pressure reestablished, this safety circuit automatically trips over again into the "anaesthetic gas" selection position as long as the hand valve 13 remains open. In this safety circuit, with loss of the oxygen supply not only does the anaesthetic gas shutoff valve 13 close, air always flows to supply the patient.

Claims

1. Gas mixing apparatus comprising: first, second and third gas inlet lines; a mixed gas outlet line to which the first, second and third inlet lines are connected; a first valve disposed in the second line; and a second valve disposed in the third line; wherein the first and second valves are connected to, and actuatable by the pressure in, the first line; and wherein the arrangement is such that, in use, the first valve is closed and the second valve is opened when the pressure in the first line exceeds a predetermined pressure, and the first valve is opened and the second valve is closed when the pressure in the first line falls to or below that predetermined pressure.

2. A gas mixing apparatus as claimed in claim 1, wherein the first and second valves are pneumatically actuated and are connected to the first line via a control line.

3. A gas mixing apparatus as claimed in claim 2, wherein the control line includes a manually actuatable control valve.

4. A gas mixing apparatus as claimed in claim 1, 2 or 3, wherein each of the first, second and third lines includes a flow-metering device for regulating and monitoring the flow in the respective line.

5. A gas mixing apparatus as claimed in claim 4, wherein each flow-metering device comprises a regulating valve and a flow-metering tube.

6. A gas mixing apparatus as claimed in claim 5, wherein each flow-metering tube is disposed between its respective regulating valve and the mixed gas outlet line.

7. A gas mixing apparatus as claimed in any preceding claim, wherein each of the first and second valves, in addition to being actuatable by the pressure in the first line, can be actuated by one or more other means.

8. A gas mixing apparatus as claimed in any preceding claim, which is or forms part of an anaesthetic gas mixing apparatus, with the first, second and third lines, in use, being supplied with oxygen, air and an anaesthetic gas respectively.

9. A gas mixing apparatus substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.