GB2160429A

GB2160429A - Universal anaesthetic circuit

Info

Publication number: GB2160429A
Application number: GB08415664A
Authority: GB
Inventors: West Terence Benjami Beresford
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-06-20
Filing date: 1984-06-20
Publication date: 1985-12-24
Also published as: GB2160429B; GB8415664D0

Abstract

A valve which may be mounted, directly or indirectly, on the gas outlet of an anaesthetic machine and to which may be attached, directly or indirectly, a reservoir bag, an expiratory valve and a pair of co-axial breathing tubes and which consists of a cylinder (whose axis is the same as that of the co-axial tubes) within which the rotation of a specifically shaped spool changes the characteristics of the whole assembly between those of Mapleson A and Mapleson D semi-closed anaesthetic breathing circuits without altering the direction of gas-flow through the circuit. The invention allows the most efficient use of fresh gas to provide for adequate elimination of carbon dioxide in both the spontaneously breathing and the artificially ventilated patient.

Description

SPECIFICATION Universal anaesthetic circuit This invention relates to a co-axial semi-closed anaesthetic breathing circuit whose configuration may be changed by means of a valve.

The two most widely used pieces of apparatus for the delivery of anaesthetic gases and vapours from an anaesthetic machine to an adult patient are classified as Mapleson A and Mapleson D semiclosed breathing circuits. Each of these has its own individual characteristics and applications which may be assessed, in both the spontaneously breathing and the artificially ventilated patient, by reference to the amount of fresh gas which is required to be introduced into the circuit to ensure elimination of the patient's previously-expired carbon dioxide from his subsequent inspirate.

The Mapleson A circuit, when used for the spontaneously breathing patient, requires the introduction of relatively small amounts of fresh gas to ensure adequate carbon dioxide elimination and is, thereby, the most efficient circuit under these circumstances. However, when used to artificially ventilate a patient, extensive rebreathing of carbon dioxide is inevitable even when large amounts of fresh gas are introduced and, under these circumstances, it is the least efficient circuit.

The Mapleson D circuit, when used for the spontaneously breathing patient, requires the introduction of relatively large amounts of fresh gas to ensure adequate carbon dioxide elimination and is, by comparison to the Mapleson A circuit, relatively inefficient for this purpose. However, when used to artificially ventilate a patient, it requires the introduction of relatively small amounts of fresh gas to ensure adequate carbon dioxide elimination and is the most efficient circuit for this purpose.

It is therefore clear that the Mapleson A circuit is the most appropriate for use with the spontaneously breathing patient while the Mapleson D circuit is the most appropriate for use with the artificially ventilate patient and that an 'ideal' or 'universal' anaesthetic circuit would combine the characteristics of both the Mapleson A and Mapleson D circuits in a single piece of apparatus.

The present invention provides for a valve into which fresh gas may be supplied and to which may be attached a reservoir bag, an expiratory valve and a pair of co-axial breathing tubes and which consists of a cylinder (whose axis is the same as that of the direction of the fresh gas supply and the axis of the co-axial tubes) within which the rotation of a specifically shaped spool changes the configuration and characteristics of the complete assembly between Mapleson A and Mapleson D circuits.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:~ Figure 1 shows an 'exploded' view of the valve assembly and spool; Figure 2 shows a diagrammatical longitudinal vertical cross-section of the valve and associated attachments in Mapleson A mode; Figure 3 shows an equivalent cross-section of a standard Mapleson A circuit (Lack); Figure 4 shows an equivalent cross-section of the valve and associated attachments in Mapleson D mode; Figure 5 shows an equivalent cross-section of a standard Mapleson D circuit (Bain).

As may be seen from the drawings, the valve in Mapleson A mode allows the supply of fresh gas (1) to be in continuity with the reservoir bag (2) and the space between inner and outer co-axial tubes (3) and it is from here that gas is available for inspiration. Simultaneously, the lumen of the inner co-axial tube (4) is in continuity with the channel through the spool (5) of the valve (6) and thence with the expiratory valve (7) and it is through this route that expiration takes place once the reservoir bag is full and the pressure in the circuit rises sufficiently to open the expiratory valve. This is also the configuration of the standard Mapleson A circuit (Lack).

Rotation of the spool (5) by means of the selector switch (8) to the Mapleson D mode of the valve takes the reservoir bag out of continuity with the supply of fresh gas (which is now delivered directly through the space between the inner and outer co-axial tubes to the patient end of those tubes) and into continuity with the channel through the spool, the expiratory valve and the lumen of the inner co-axial tube through which both inspiration and expiration now takes place. This is also the configuration of the standard Mapleson D circuit (Bain) albeit with the functions of the inner and outer co-axial tubes reversed. Rotation of the spool in the reverse direction within the valve changes the Mapleson D mode back to the Mapleson A mode.

The spool is mounted in the cylinder of the valve such that a gas-tight seal is formed between its circumference and the inner surface of the cylinder and also between its centre channel and the end of the inner co-axial tube. The outer co-axial tube is attached also by a gas-tight seal to the cylinder of the valve. The spool is secured in place within the cylinder of the valve by the detachable screwthreaded end (9) of the valve which also provides for attachment to the gas outlet of an anaesthetic machine.

Claims

1. A valve into which fresh gas may be supplied and to which may be attached, directly or indirectly, a reservoir bag, an expiratory valve and a pair of coaxial breathing tubes and which consists of a cylinder (whose axis is the same as that of the coaxial tubes) within which the rotation of a specifically shaped spool changes the characteristics of the complete assembly between those of a Mapleson A and a Mapleson D semiclosed co-axial anaesthetic breathing circuit without changing the direction of gas-flow through the circuit.

2. A valve as claimed in Claim 1 in which the rotating spool is so shaped that it is a cylinder which has a segment removed from the appropriate portion of its circumference to allow direct communication between fresh gas supply, aperture of reservoir bag and the space between inner and outer co-axial tubes when in position for Mapleson A mode and which has holes bored through it both axially and radially that allow communication between the lumen of the inner co-axial tube and the expiratoryvalve outlet when in position for Mapleson A mode and between the lumen of the inner co-axial tube, expiratory valve outlet and reservoir bag outlet when in position for Mapleson D mode.

3. A valve as claimed in Claims 1 and 2 in which both cylinder and spool are tapered and/or springloaded.

4. A valve as claimed in Claims 1, 2 and 3 which may be mounted directly on the gas outlet of an anaesthetic machine and whose axis is the same as that of such a gas outlet.