GB2208202A

GB2208202A - Anaesthetic gas scavenging reservoir

Info

Publication number: GB2208202A
Application number: GB8516871A
Authority: GB
Inventors: R J A Gil-Rodriguez
Original assignee: Automated Process & Control
Current assignee: Automated Process & Control
Priority date: 1984-07-03
Filing date: 1985-07-03
Publication date: 1989-03-15
Also published as: GB2208202B; GB8416904D0; GB8516871D0

Abstract

An anaesthetic gas scavenging system comprises a co-axial open reservoir with a patient connection tube 21 terminating within the reservoir. An end piece 22 is fitted to the tube, the end piece having inlet and outlet openings directed in the same direction so that the end piece reverses the flow direction of the exhaust gases in receiving them from the tube and passing them to the reservoir for removal at 31 by suction. Air holes 24, 25 are provided at the bottom of the reservoir. <IMAGE>

Description

ANAESTHETIC GAS SCAVENGING SYSTEMS This invention relates to anaesthetic gas scavenging systems, particularly of the coaxial open reservoir active kind.

Reference will now be made to Figures 1 and 2 of the accompanying diagrammatic drawings in which: Figure 1 is a known kind of anaesthetic gas scavenging system; and Figure 2 shows 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 a patient breathing circuit (not shown) are collected in a collecting system 10 which includes a ducted expiratory valve 11.

A conical connector 12 couples the valve to a transfer tube 13 through which the gases are passed. A receiving system 14 comprising a vessel 15 closed at one end and open to the atmosphere at the other end is provided and the gases are voided into the closed end of the vessel as a series of intermittent pulses. A disposal or scavenging 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 an injection phase (patient expirtlzj 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 according to the orientation of the patient connection tube in relation to the scavenging connection. The systems shown are: (i) Top injection (ii) Cross-flow injection.

(iii) Co-axial injection.

(lav) Oblique inJection.

Patient safety with open reservoir active 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 presssures 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 transmit suction pressures and flows to the expiratory valve 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 hypoxia, atelectosis, pulmonary oedema and barotrauma.

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

According to the invention there is provided a coaxial open reservoir for an active anaesthetic gas scavenging system wherein there is a patient connection tube terminating within the reservoir, and an end-piece tube fitted to the end of the tube within the reservoir, the end-piece ha#ing inlet and outlet openings directed in the same direction, the inlet opening being adapted to couple with the end of the tube, the end-piece thus reversing the flow direction of the exhaust gases in receiving them from the tube and passing them to the reservoir.

Preferably the end-piece is T-shaped.

An embodiment of the invention will now be described with reference to Figure 3 to 5 of which: Figure 3 is a cross-section through a co-axial injection active open-reservoir scavenging system incorporating the present invention; Figure 4 is a cross-sectional view of a pressure and flow inhibitor for use in a scavenging system according to the present invention; and Figure 5 is an underside view of the inhibitor of Figure 4.

Referring to Figures 3 to 5 the transfer tube 4 from the collecting system 10 is connected to a patient connection tube 20 of a coaxial injection active open reservoir scavenging system, which tube 20 has an extension 21. At the end of the extension 21, remote from the collecting system is a T-shaped pressure and flow inhibitor 22. Surrounding and enclosing the extension 21 and pressure and flow inhibitor 22 is a cylinder 23, which cylinder is screw threadedly secured to the periphery of an annular flange 26 formed integrallly with the patient connection tube 20. An annular reservoir 27 is thus defined between the extension 21 and the cylinder 23. The reservoir 27 is open to the atmosphere by way of inlet orifices 24 located in the cylinder and inlet orifices 25 located in the annular flange 26.

Towards the end of the cylinder remote from the connection tube 20 and beyond the inhibtor 22 are a flow indicator 28, a clear window 29 and a flow regulating valve 30.

The end of the cylinder 23 remote from the connection tube 20 is connected to the air mover 17 and thus a constant suction is applied to the cylinder, the scavenger flow being represented by an arrow 53.

The pressure and flow inhibitor 22 has two kidney shaped outlets 22a which face the opposite direction to the air flow in the reservoir represented by arrows 52 and caused by the suction created by the air mover 17. The flow of waste anaesthetic gases in the extension 21 is represented by arrow 50 and is parallel to the air flow in the reservoir 27.

Upon passing through the pressure and flow inhibitor the flow of waste anaesthetic gases diverges and emerges from the outlets 22a in the opposite direction 51 to the air flow in the reservoir.

The effect of the inhibitor 22 is to alter the pressure in the patient connection tube 20, in such a way as to produce a very small positive pressure in tube 20 (less than 1 pa). In comparison, without the inhibitor, a negative pressure is present in the patient connection tube 20. This small positive pressure totally inhibits any suction flow in the patient connection tube for an extract scavenge flow rate of 100 to 500 litres per minute and does not produce any significant increase in expiratory resistance. It is found that functioning of the inhibitor is enhanced if its dimensions are such that the combined area of the outlets 22a is approximately equal to the area of the central inlet hole.

The invention is not restricted to the details of the embodiment described with reference to the aceempanying drawings. For example, the end-piece may be other than T-shaped - a mushroom shape or a cruciform shape are suitable alternatives.

Claims

1. A co-axial open reservoir for an active anaesthetic gas scavenging system wherein there is a patient connection tube terminating within the reservoir, and an end-piece fitted to the end of the tube within the reservoir, the end-piece having inlet and outlet openings directed in the same direction, the inlet opening being adapted to couple with the end of the tube, the end-piece thus reversing the flow direction of the exhaust gases in receiving them from the tube and passing them to the reservoir.

2. A co-axial open reservoir as claimed in claim 1 wherein the end piece is T-shaped.

3. A co-axial open reservoir substantially as hereinbefore described with reference to Figures 3 to 5 of the accompanying drawings.