GB2228419A

GB2228419A - Anaesthetic gas scavenging

Info

Publication number: GB2228419A
Application number: GB9001959A
Authority: GB
Inventors: Dr J A Gill-Rodriguez
Original assignee: Automated Process & Control
Current assignee: Automated Process & Control
Priority date: 1989-01-27
Filing date: 1990-01-29
Publication date: 1990-08-29
Anticipated expiration: 2010-01-29
Also published as: GB8901776D0; GB9001959D0; HK17893A; GB2228419B

Abstract

An open reservoir or air break anaesthetic gas scavenging system has an inlet port of the reservoir 15 including a on-way valve (1) to allow the passage of gases from the patient but to prevent the effects of suction from an air mover 17 being experienced by the patient. The system further comprises a ducted adjustable pressure limited expiratory valve 11, a transfer tube 13, the reservoir 15 having one open end and a closed end, which pulsed expiratory gas enters through the one way valve, and an air mover 17 discharging air to the outside at E. The valve is preferably a biased membrane flap valve. Figs 2 and 5 (not shown) show alternative arrangements of the inlet and outlet of the reservoir. <IMAGE>

Description

ANAESTHETIC SYSTEM PRESSURE AND FLOW INHIBITOR This invention relates to active anaesthetic gas scavenging systems of the open reservoir kind, known generally as airbreaks.

Reference will now be made to Figures 1 and 2 of the accompanying schematic drawings of which: Figure 1 is a diagram of a known open reservoir active anaesthetic gas scavenging system; and Figure 2 is a diagram showing various ways in which waste anaesthetic gases can be voided into a reservoir vessel.

Referring to Figure 1, polluted anaesthetic gases exhaled by the patient from the breathing circuit of the anaesthetic machine (now shown) are collected in a collecting system 10 which includes a ducted adjustable pressure limited (APL) expiratory valve 11. A conical connector 12 couples the valve to the transfer tube 13 through which the gases are passed. A receiving system 14 comprising a reservoir vessel 15 closed at one end and open to the atmosphere at the other end is provided and the waste gases are voided into the closed end of the vessel as a series of intermittent pulses. A disposal system 16 comprising an air mover 17 draws off the contents of the vessel 15 as a continuous flow along a tube 18 to an external termination E which is situated outside the operating theatre.

When the instantaneous flow rate from the collecting system exceeds the steady flow rate extracted by the air mover, excess gases pass down the vessel, which acts as a reservoir, to be removed at the end of the injection phase (patient exhalation) together with room air flowing through the vessel.

Referring to Figure 2, in which I represents the injection of waste anaesthetic gases and S represents the scavenging gas flow, there are various ways in which the polluted gases can be voided into the reservoir vessel of the receiving system. It is possible therefore to classify open reservoir active systems (airbreaks) according to the orientation of the patient connection tube in relation to the scavenging connection. The systems shown are: (1) Top injection (2) Cross-flow injection (3) Co-axial injection (4) Oblique injection Patient safety with open reservoir active anaesthetic gas scavenging systems depends upon the presence, at all times, of unobstructed air entry through the open end of the receiving vessel. In theory, this avoids the building up and transmission of suction pressures from the air mover across the open reservoir to the breathing circuit of the patient.In practice, however, this is not the case and all open reservoir active systems (airbreaks) transmit suction pressures and flows to the expiratory valve (APL) and across the valve to the breathing circuit and finally to the patient's airway.

This suction can produce scavenging of fresh anaesthetic gases and can cause in the patient hypoxia, atelectasis and pulmonary oedema.

The present invention seeks to provide a solution to this problem.

According to the invention there is provided an anaesthetic gas scavenging system of the open reservoir kind including an elongate reservoir vessel open at one end to the atmosphere and having at the other end an inlet port for receiving waste anaesthetic gases from the patient and an outlet port to a scavenging gas connection, there being provided an end piece which fits the inlet port and which has a one-way valve which opens to receive patient exhalation but which prevents transmission of suction from the outlet port via the inlet port to the patient. Thus, the end piece is provided to fit at the point where the polluted gases are voided into the reservoir vessel of the receiving system I in Figure 2.This end-piece is fitted with a valve such as to open only when the patient exhalation reaches it but it will not be opened by the transmitted suction pressure from the air mover across the receiving vessel.

It is possible to achieve this with different kinds of valve. The valve may be unbiased or biased to the closed position with a spring or by virtue of inherent resilience of the valve closure member. In a preferred embodiment of the invention the valve is a membrane flap valve of a suitable pliable material retained on its edge at a single point and able of opening only to the inside of the vessel in the direction of the patient's exhaled flow of gases.

An embodiment of the invention will now be described with reference to Figures 3 to 5 of which: Figure 3 is a cross section through a pressure and flow inhibitor according to the present invention showing the membrane flap in its closed position; Figure 4 is a cross section similar to Figure 3 showing the membrane flap in its open position; and Figure 5 is a set of diagrams showing the pressure and flow inhibitor fitted to the patient connection tube of the various types of airbreaks as previously described.

Referring to Figures 3 and 4 the inhibitor comprises a hollow frusto-conical end-piece 1 with a cylindrical plug section 2 at one end and a flap valve 4 at the other. The inhibitor or end piece is a plug fit in the inlet port of the reservoir. The flap valve comprises a membrane of pliable plastics materials of circular shape fixed at one point near its periphery by a screw 5.

Figure 5 shows the inhibitor plugged into the inlet tube of the various airbreaks described.

It is found that in preferred embodiments the present invention completely inhibits the induced flow present in all types of active anaesthetic gas scavenging systems of the open reservoir kind. By the use of the invention and with an extract scavenging flow of up to 130 litres per minute, the induced flow is totally eliminated and no induced flow can be recorded.

The invention does not produce a significant increase in resistance to gas flow when measured at 30 and 90 litres per minute.

Claims

1 An anaesthetic gas scavenging system of the open reservoir kind including an elongate reservoir vessel open at one end to the atmosphere and having at the other end an inlet port for receiving waste anaesthetic gases from the patient and an outlet port to a scavenging gas connection, there being provided an end piece which fits the inlet port and which has a one-way valve which opens to receive patient exhalation but which prevents transmission of suction from the outlet port via the inlet port to the patient.

2 An anaesthetic gas scavenging system as claimed in Claim 1 wherein the valve is biased to the closed position.

3 An anaesthetic gas scavenging system as claimed in Claim 1 or Claim 2 wherein the valve is a membrane flap valve.

4 An anaesthetic gas scavenging system as claimed in any of the preceding claims wherein the end piece is a plug which fits the inlet port.

5 An end piece for an anaesthetic gas scavenging system as claimed in Claim 4 which is adapted to be a plug fit in the inlet port.