GB2162757A - An anaesthetic breathing system - Google Patents

Abstract

An anaesthetic breathing system comprising a pair of co-axial tubes (20,21) an anaesthetic supply tube (15), a flexible reservoir bag (16), an expiratory valve (17) and a ventilator port (18). For spontaneous respiration, a rotary valve (25) connects tubes (15) and (21) to bag (16) and tube (20) to expiratory valve (17). For mechanical ventilation, valve (25) is rotated to occlude bag (16) and valve (17) and to open outer tube (20) to ventilator port (18) which may be connected to a mechanical ventilator. <IMAGE>

Description

SPECIFICATION An anaesthetic breathing system This invention relates to an anaesthetic breathing system with means for selecting different modes of operation for spontaneous and controlled mechanical ventilation, as required.

An obje#ct of the present invention is to provide a system which combines efficiency during spontaneous and manually controlled ventilation, with convenience for use with a mechanical ventilator.

According to the present invention there is provided an anaesthetic breathing system comprising a pair of co-axial tubes, the inner connecting a face mask or breathing nozzle for the patient to an anaesthetic gas supply menas, the outer connecting said mask or nozzle to an expiratory valve, a flexible reservoir bag connected to said inner tube and said gas supply means, a ventilator port in said outer tube for connection of said outer tube to a mechanical ventilator, and a rotary valve rotatable co- axially with respect to said inner and outer tubes between a first position in which it occludes said ventilator port, and a second position in which it occludes said reservoir bag and said expiratory valve.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 illustrates five different known kinds of anaesthetic breathing system; and Figure 2 illustrates a system made in accordance with the invention.

The simplest anaesthetic breathing systems employ a single tube to deliver gases from the anaesthetic supply to the patient. Five such systems have been described by William W. Mapleson in 1954 and have come to be recognised by the letters A to E as illustrated in Figure 1. Such systems operate without carbon dioxide absorbers and rely upon an adequate flow of anaesthetic gas to prevent undue mixture of the latter with expired gas and thus re-breathing of expired gas. System A requires a fresh gas flow rate during spontaneous ventilation, of about 0.7 times the patient minute volume. Systems B to E however are less efficient and require fresh gas flow rates of more than twice the minute volume in order to prevent re-breathing of the expired gas.

The advantage with System A during spontaneous ventilation is achieved by the position of a reservoir bag 10 between-the fresh gas inlet 11 and the face.mask 12. The bag 10 allows the flow of gas in the delivery tube 13 to be regulated by the patient's breathing. This results in clear separation between fresh gas and expired gas, the latter being allowed to escape via expiratory valve 14.

By contrast, in Systems B to E, fresh gas enters at a point close to the patient's mouth during all phases of respiration and a high degree of mixing of the expired gas with the fresh gas is experienced so that much higher gas flow rates are required to keep these systems adequately flushed.

System A however has certain disadvantages. It is difficult to adapt for use with a mechanical ventilator owing to the presence of the compliant reservoir bag and an intermittent leak from the expiratory valve. The expiratory valve 14 being located close to the patient's face is somewhat inaccessible to the anaesthetist.

Some of these difficulties have been overcome by known systems which include a pair of co-axial tubes one of which carries fresh anaesthetic gas to the patient whilst the other carries expired gas to the expiratory valve or other outlet. These co-axial systems whilst overcoming certain of the difficulties experiences with single-tube systems, still do not exhibit equal efficiency and/or convenience whether in the spontaneous or mechanical respiration mode.

The present invention is based upon an appreciation of the advantage of combining the principles of Systems A and E in Figure 1 with a co-axial breathing attachment thus to ensure good performance in both modes of operation.

Referring now to Figure 2, it will be seen that there is provided a rigid fresh gas supply tube 15 with which communicates a flexible reservoir bag 16, an expiratory valve 17 and a ventilator port 18 for attachment of a mechanical respiratory system.

Tube 15 is readily attachable to the outlet of an anaesthetic gas supply machine. The other end of tube 15 has attached thereto a co-axial breathing attachment generally indicated at 19 and comprising an outer flexible tube 20 and an inner flexible tube 21. Inner tube 21 is connected to a rigid tube 22 which is supported within tube 15 by a radial support device 23. Attached to the free end of outer tube 20 is a breathing mask 24. A further ra dial support member (not shown) is conveniently disposed close to the free ends of tubes 20 and 21.

A rotary valve generally indicated at 25 is positioned within tube 15 and is rotatable co-axially with respect to the latter and to tubes 20, 21 and 22. Valve 25 comprises a thick walled barrel 26 which forms a gas-tight seal between tubes 15 and 22. Axially extending with respect to barrel 26 of valve 25 and attached thereto, is a thin walled barrel 27 which is of the same outer diameter as barrel 26 but has an enlarged bore as indicated by reference numeral 28.

Valve 25 is open at both ends and includes radial ports 29 and 30 which in the position shown in Figure 2 communicate respectively with the reservoir bag 16 and expiratory valve 17. Valve 25 includes an operating handle 31 which may be turned through 90 thus to rotate barrels 26 and 27 from the position illustrated in Figure 2 to a second position in which port 29 no longer communicates with reservoir 16 and thus occludes same, and port 30 no longer communicates with expiratory valve 17 but instead communicates with ventilator port 18.

Valve 25 is preferably associated with a gatetype release mechanism so that handle 31 cannot be turned inadvertently. This can be provided by requiring a small degree of axial movement of valve 25 against a spring before rotation can be achieved.

A pressure limiting valve 32 on tube 15 is preferably included and preset to open at an internal pressure of 50 cms water gauge.

In operation, for normal spontaneous ventilation, the patient inhales fresh anaesthetic gas through tube 15, reservoir bag 16, valve 25, tube 22 and 21, and exhales expired gas via tube 20 to expiratory valve 17 from which it escapes.

When it is required to operate the device for controlled mechanical ventilation, handle 31 is moved to rotate Valve 25 to the position in which reservoir bag 16 and expiratory valve 17 are occluded and a mechanical ventilator system attached to ventilator port 18 is activated. In this mode expired gases from the patient are discharged via port 18 and the ventilator.

In this mode the system approximates closely to System E illustrated in Figure 1 whilst in the normal spontaneous respiratory mode with the valve 25 in the position shown in Figure 2, the system is similar to System A but with a co-axial breathing tube attachment with the reservoir bag 16 communicating predominantly with fresh gas inner tube 21, expired gas in outer tube 20 passing exclusively to expiratory valve 17.

Since valve 25 is positioned co-axially within tube 15 and expiratory valve 17 is located close to reservoir bag 16, the device is compact with its parts readily accessible to the anaesthetist and only the #breathing tubes being directed to the area close to the patient. The system facilitates controlled operation by the anaesthetist and rapid and complete conversion from a spontaneous respiratory system to a controlled mechanical system.

With the ventilator port 18 already attached to a mechanical ventilator, all that is required to convert the system from spontaneous to assisted respiration is for handle 31 to be turned to the appropriate position.

It is not intended to limit the invention to the above example only, many variations, such as might readily occur to one skilled in the art, being possible without departing from the scope of the invention.

For example, the thickened wall of barrel 26 can be replaced by a sealing ring or sleeve attached to the sleeve of valve 25 which thus may be of constant diameter throughout, and bearing against the external surface of tube 22, or alternatively such a sealing ring can be attached to tube 22 and bear against the internal wall surface of the valve. Such modifications could render the device simpler in manufacture since valve 25 would be constituted by a composite sleeve member incorporating sections 26 and 27.

Claims (9)

1. An anaesthetic breathing system comprising a pair of co-axial tubes, the inner connecting a face mask or breathing attachment for the patient to an anaesthetic gas supply means, the outer connecting said mask or attachment to an expiratory valve, a flexible reservoir bag connected to said inner tube and said gas supply means, a ventilator port in said outer tube for connection of said outer tube to a mechanical ventilator, and a rotary valve rotatable co-axially with respect to said inner and outer tubes between a first position in which it occludes said ventilator port, and a second position in which it occludes said reservoir bag and said expiratory valve.

2. An anaesthetic breathing system according to Claim 1, wherein said rotary valve comprises a sleeve having an axial bore one end of which is open to and in communication with said inner tube whilst the other end is open to and in communication with said outer tube, the inner and outer wall surfaces of the sleeve being in gas tight sealing engagement with the inner and outer co-axial tubes respectively.

3. An anaesthetic breathing system according to Claim 1 or Claim 2, wherein said rotary valve comprises a thick-walled barrel forming a gas-tight seal between said inner and outer tubes, and a thin-walled barrel extending axially with respect to the-thick-walled barrel and attached thereto, said thick and thin-walled barrels being of the same outer diameter whilst said thin-walled barrel has an enlarged axial bore, a radial port in said thickwalled barrel communicating with said reservoir bag, a further radial port in said thin-walled barrel communicating alternatively with said expiratory valve or said ventilator port.

4. An anaesthetic breathing system according to Claim 1, wherein said rotary valve, in said second position provides a direct communication between the ventilator port and said outer tube.

5. An anaesthetic system according to any preceding claim, wherein said rotary valve includes an operating handle accessible to enable rotation of said rotary valve between its first and second positions, and a release mechanism preventing it from being rotated inadvertently.

6. An anaesthetic breathing system according to any preceding claim, wherein said flexible reservoir bag is interposed between said face mask and the end of said inner tube to be connected to the anaesthetic gas supply means.

7. An anaesthetic breathing system according to any preceding claim, wherein said expiratory valve, said ventilator port and said reservoir bag are located in close proximity, and remote from said face mask or breathing attachment.

8. An anaesthetic breathing system according to any preceding claim including means supporting said inner tube co-axially within said outer tube.

9. An anaesthetic breathing system substantially as hereinbefore described, with reference to Figure 2 of the accompanying drawings.