GB2162070A - Anaesthetic systems and valves therefor - Google Patents

Abstract

The invention provides a valve means 6 which can readily switch anaesthetic systems between Mapleson A, Mapleson D and circle modes in a single positive movement. This is achieved by means of a two, or three- way valve, which causes gases to flow along a predetermined path in accordance with a selector means 7. <IMAGE>

Description

SPECIFICATION Anaesthetic systems and valves therefor The present invention relates to anaesthetic systems and to valves therefor. The present invention relates in a first aspect to Mapleson type A and D anaesthetic systems which are commonly adopted in current medical practice. In Mapleson type A system an expiratory valve is positioned close to a face mask which is separated by a length of tube from a reservoir bag and a supply of fresh gases.

In a Mapleson type D system a supply of fresh gases is supplied close to the face mask, which is separated by a corrugated tube from a reservoir bag and the expiratory valve. These systems are shown diagrammatically in Figures 1 and 2 respectively accompanying this specification (see Brit. J.

Anaesth. (1954) 26 P 323).

An alternative system is shown in Figure 2a. This shows the circle system in which expired air from a patient is cleaned in a CO2 absorber, and returned to the patient via a one way valve system. This system has certain advantages and is popular in some countries.

Overthe last few years Mapleson systems AD and the circle system have been generally used.

However, problems have arisen in switching from systems A to D for example and back again during anaesthesia. The circle system has not been generally available with these two other systems because of the complexities of switching between the three systems with the degree of assurance required in the operating theatre.

One attempt to overcome the problem of switching between Mapleson A and D systems has been described in Br. J. Anaesth. (1979), Vol.51, p.1185. This disclosure relates to a valve device for converting a coaxial Mapleson D into a coaxial Mapleson A system and vice versa. In this disclosure a coaxial valve is described wherein fresh gases entering the valve via a port are selectively caused to flow either along an exterior corrugated tube or along a coaxial inner tube depending upon the system selected. The valve is provided with a downwardly depending T-junction for attachment to a reservoir bag which connects directly with the exterior coaxial tube. The expiratory valve is positioned adjacent the fresh gas inlet and accordingly in the Mapleson D mode the expiratory valve is positioned downstream of the bag.

This arrangement has led to the criticism that re breathing will occur in use during the changeover from spontaneous to controlled ventilation. This is because at the moment of changeover the gases that were in the expiratory limb now become the gases which will be inspired on the next breath.

An attempt to overcome this problem for both coaxial and non-coaxial systems has been described in Anaesthesia, 1983, Volume 38, pages 361 to 372-D. Humphrey.

This disclosure describes a two lever device for switching from the one system to the other. The difficulties in this approach lie in utilizing two counter-rotating valves in the changeover from spontaneous respiration to controlled ventilation.

This is at least confusing to the uninitiated and is potentially hazardous. Manipulation of two separate levers, one of which has an additional half-cocked position to allow manual ventilation in the D configuration does not lead to maximum safety.

Indeed, incorrect positioning of the levers can often cause dangerous rises in pressure.

The present invention seeks to provide, therefore, a much simplified system for switching between Mapleson A, Mapleson D and circle modes, which reduces as far as possible the problems of rebreathing and of switching between desired systems with a maximum of safety.

Accordingly, in one aspect of the present invention there is provided an anaesthetic system comprising an inspiratory limb terminating in a face mask, an expiratory limb operatively connected to the face mask and having disposed thereon an expiratory valve, and a reservoir bag; characterised in that the reservoir bag may be switched by a valve into operative connection with the inspiratory limb upstream of the face mask (mode A) or with the expiratory limb downstream of the face mask and the expiratory valve (mode D).

The system may be provided with two limbs in parallel terminating adjacent the face mask in a Ypiece connector therefor. The parallel limbs may be spaced slightly apart and provided therebetween with a valve which may comprise a first bore extending to the inspiratory limb, and a second bore extending to the expiratory limb, and a main bore connecting the neck of the reservoir bag, and switch means movable in a single movement between the first and second bores while blocking the other one of said bores thereby to select mode A or D. The switch may be formed of an internal coaxial cylinder disposed on the internal bore of an external cylinder block, the said internal bore closely cooperating with the external bore of the inner cylinder. The inner cylinder may be provided with a single bore in its wall, and with connection means to the reservoir bag at its lower extremity.The exterior cylinder may be provided with two bores, one to the inspiratory limb, and one to the expiratory limb. Accordingly, rotation of the inner cylinder relative to the outer cylinder between the first and the second positions brings the bore in the inner cylinder into register with either one of the two bores to form mode A or D as required.

According to another aspect of the invention, there is provided a switch for use in an anaesthetic system which comprises a switch block comprising a generally vertical bore of comparatively large diameter communicating in a first direction with an inspiratory limb and in a second direction with an expiratory limb, said bore terminating toward its lower extremity in a connector for a reservoir bag, and in its upper extremity with closely fitting cylindrical hollow selector means provided with a single bore in the wall thereof, the arrangement being such that rotation of the selector means through a desired angle connects the reservoir bag exclusively to the inspiratory or the expiratory limb.

The switch block as just described may carry thereupon an expiratoryvalve adapted to be situated between the reservoir bag and the face mask in use. It will thus be appreciated that movement of the selector means at an angle of, for example, 90 degrees will connect the reservoir bag either into its Mapleson A or Mapleson D modes.

In another embodiment the switch block may be additionally provided in its vertical bore with a second pair of interconnections, and wherein the selector means simultaneously is provided with bores in the wall thereof. The second pair of interconnections may be angularly offset relative to the interconnections to the expiratory and inspiratory limbs, whereby the selector means may be moved to any of three operative positions to respectively select, A, D and circle modes.

Such a switch, if it is to be used in association with the circle mode, is associated with a separate carbon dioxide absorber and one way valve assembly.

Thus, in a third aspect of the invention valves and anaesthetic systems of the above type are provided, but wherein, in a third mode, the circle mode may be alternatively and exclusively selected.

In this third aspect the system may be switched between A, D and circle modes at will in a single movement. This is achieved by providing an anaesthetic system comprising an inspiratory limb terminating at a face mask, an expiratory limb operatively connected to the face mask and having an expiratory valve disposed thereon and a reservoir bag, characterized in that the reservoir bag may be switched by a valve into operative interconnection with the inspiratory limb upstream of the face mask (A); with the expiratory limb downstream of the face mask and the expiratory valve (D); or into a circle mode wherein expired air is passed via a carbon dioxide absorber to the expiratory limb.

The switch may be formed of an internal coaxial cylinder disposed internally of an external cylinder block, said internal bore closely co-operating with the bore of the block, and terminating in a connection means to a reservoir at its lower extremity.

The inner cylinder may be provided in its wall with a single upper bore, and a double lower bore offset from the upper bore by an angle of, for example 900.

The exterior cylinder may be provided with two upper bores and two lower bores, preferably respectively in register one above the other.

Accordingly, rotation of the inner cylinder relative to the outer cylinder in a first and third position provides A and D modes because the single upper bore interconnects either with the fresh gas supply or with the expiratory valve. At a point preferably intermediate the A and D positions, the double lower bore provides a common path for cleaned gas from a carbon dioxide absorber to the fresh gas supply, while the A and D modes remain obturated.

The invention will now be described, by way of illustration only, with reference to the accompanying drawings, wherein:- Figures 1,2, and 2a represent in plan a diagrammatic view of Mapleson A and Mapleson D and circle type systems in accordance with the prior art, Figure 3 shows a side view from above of a two way system in accordance with the present invention, Figures 4 and 4a show in part-section the gas flow with the switch in the A position, and Figures 5 and 5a show the gas flow with the switch in the D position.

Figure 6 shows a side view of a three way valve according to the invention, Figure 7 shows a transverse cross-section along a line A: A of Figure 6, Figure 8 shows a vertical cross-section along a line B: B of Figure 7, and Figures 9a to c show the three-way valve diagrammatically in operation.

With reference to the prior art shown in Figures 1, 2 and 2a, fresh gases enter the Mapleson A system in the direction of the arrow in Figure 1, and pass along the inspiratory limb to the face mask 3. On exhalation breathed gases escape to the atmosphere via an expiratory valve 2. A reservoir bag connects with the inspiratory line and is utilized in the normal way.

With reference particularly to Figure 2, the Mapleson D system provides an inspiratory line 1 through which a supply of fresh gases is directed in the direction of the arrow. Fresh gases reach the face mask 3 and on exhalation pass along the expiratory limb 5 past the entrance to the reservoir bag 4, and to the exterior via the expiratory valve 2.

Figure 2a shows a circle system wherein fresh gas enters along a line 1 and passes via a face mask 3 to a a patient. Expired air then passes an expiratory valve which opens only on occasion and, thus, usually forces expired air via a carbon dioxide absorber 20 and a one way valve 21 back into the fresh air system 1 again. The reservoir 4 is positioned between the absorber 20 and the fresh gas supply 1.

An embodiment of the invention is now described with reference to Figures 3 to 5a. The inspiratory limb 1 is formed as part of a unitary block 10. Means are provided to attach said inspiratory limb 1 to a corrugated collector piece 1A which terminates in a Y-type connector and face mask (not shown). The switch block 10 is also provided with expiratory limb 5 extending in parallel to the inspiratory limb 1 and carrying thereupon an expiratory valve 2. The expiratory valve 2 again is connected by means of the corrugated connector 5A to the 'Y' connector and face mask.

Depending from the lower surface of the switch block 10 is a reservoir bag connector limb 11 which extends downwardly and approximately perpendicular to the expiratory and inspiratory limbs. The reservoir bag 4 may be affixed to the limb 11 in standard fashion.

With particular reference to Figures 4 and 5, it will be noted that the switch block 10 is provided with a cylindrical bore 9, which bore 9 is provided with an inspiratory aperture connecting the said bore 9 with the interior of the inspiratory limb 1, and with an expiratory aperture 12 connecting the expiratory limb 5 with the said bore 9. An operating means 7 is provided with an operating knob situated superior to an outwardly directed flange. Situated below the flange is a hollow cylinder provided on one of its faces with a single slot 8 which may be turned either in the direction of the inspiratory limb or in the direction of the expiratory limb as required.It will be appreciated that because of the hollow nature of the operating means the gases may either flow direct from the inspiratory limb into the reservoir bag, or in the alternative, from the expiratory limb into the reservoir bag.

With reference now to Figures 6to 9c, Figure 6 shows a side view of a th ree-way valve in accordance with the present invention. The valve is formed of a hollow block 22 extending generally vertically. Extending transverse to the block 22 and on either side is an upper fresh gas inlet 23 provided with a bore 231 extending toward the hollow body of the block 22. Situated parallel to the inlet 23, but opposed thereto onthe other side of the block, is an upper expiratory limb 3, again interconnected with the hollow body within the block 22 by means of a bore 241. Extending parallel to and belowthe inlet 23 and the limb 24 are, respectively, a first gas outlet 25 and a second gas inlet 26.

A selector 27 is formed of a coaxial sleeve which fits within the hollow body of the block 22 and is provided with a connecting bore 30 toward its upper extremity and with a pair of diametrically opposed lower bores 31 respectively interconnecting the bores 251 and 261. The sleeve 27 opens at its lower extremity into a reservoir bag connector 28.

It will be apparent that rotation of the selector 27 into the position shown in Figures 7 and 8 interconnects the inlets 25 and 26 while ensuring that the bores 24 and 25 are shut off. This means that the circle mode anaesthesia can be conducted exclusively. Movement of the sleeve 27 through 90 for example will connect either one of the inlets 23 or 24, while shutting off the circle mode operation, thereby allowing either Mapleson A or D modes to be selected, exclusively.

This is shown, diagrammatically, in Figures 9a, 9b and 9c.

Of course, if desired the valve can be arranged to provide Mapleson A and circle modes only, or Mapleson D and circle modes only, as desired. It will be apparent to those skilled in the art what changes are necessary to the valve in order that this may be achieved.

Claims (9)

1. An anaesthetic system comprising an inspiratory limb terminating in a face mask, an expiratory limb operatively connected to the face mask and having disposed thereon an expiratory valve, and a reservoir bag; characterised in the provision of a valve, adapted to switch the reservoir bag into operative interconnection with either the inspiratory limb upstream of the face mask (mode A) or with the expiratory limb downstream of the face mask and the expiratory valve (mode D).

2. A system according to claim 1, additionally comprising a carbon dioxide absorber and a one way valve assembly, characterised in that the valve is additionally adapted to exclusively switch the inspiratory limb into operative connection with the carbon dioxide absorber and one-way valve assembly, thereby to provide a circle anaesthesia mode.

3. A system according to claim 2 wherein the valve is adapted to select a circle mode at a position intermediate the A and D modes.

4. An anaesthetic system valve comprising a switch block comprised of a generally vertical bore of comparatively large diameter, communicating in a first direction with an inspiratory limb and in a second direction with an expiratory limb, said bore terminating toward its lower extremity in a connectorfora reservoir bag, and in its upper extremity with a closely fitting cylindrical hollow selector means provided with a single bore in a wall thereof, whereby rotation of the selector means through a desired angle connects the reservoir bag connector exclusively with the inspiratory or the expiratory limb.

5. A valve according to claim 4 wherein the switch block is additionally provided in its vertical bore with a second pair of interconnections and wherein the selector means is provided with second bores in the walls thereof, the second pair of interconnections being angularly offset relative to the connectorforthe inspiratory and expiratory limbs, whereby the selector means may be moved to any of three operative positions to respectively select A, D and circle modes.

6. A valve according to claim 5 wherein the selector means selects the circle mode at a switch position intermediate A and D modes.

7. A valve according to claim 6 wherein the second valve interconnections are provided by a horizontal bore perpendicular to the axis of the single bore.

8. A valve substantially as hereinbefore set forth with reference to, and illustrated in Figures 3 to 9 of the accompanying drawings.

9. An anaesthetic system substantially as hereinbefore set forth with reference to and as illustrated in Figures 3 to 9 of the accompanying drawings.