GB2221163A

GB2221163A - Gas scavenging apparatus

Info

Publication number: GB2221163A
Application number: GB8915743A
Authority: GB
Inventors: Harris Henry Mccrea
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-07-29
Filing date: 1989-07-10
Publication date: 1990-01-31
Also published as: GB8915743D0; GB8818154D0

Abstract

Gas scavenging apparatus for connection to a patient breathing system which draws air through a receiver body 1 and employs a Venturi to provide suction of gases from the patient inlet tube 4, the open enlarged end of which faces the air flow through the body 1, the flow rate of the air through the receiver body and the dimensions of the apparatus being chosen such that the patient's breath is not sucked away too rapidly. The receiver body 1 may have a transparent portion 6 within which is movable a piston 11 to act as a flow rate indicator. <IMAGE>

Description

GAS SCAVENGING APPARATUS This invention relates to gas scavenging apparatus.

When anaesthetic gas is used it is necessary to protect personnel from excessive exposure to the gas, and thus it is necessary to scavenge expired or excess anaesthetic gases from patient breathing systems to prevent the gas from escaping into the immediate surrounding atmosphere. This scavenging may be done actively where the scavenging system is connected directly to the patient breathing system or by passive or proximity systems where there is not direct connection to the patient breathing system. The present invention is principally concerned with active scavenging systems.

In active scavenging systems it is necessary to ensure that the scavenging apparatus does not impair the performance of the breathing apparatus to which it is connected or produce a harmful effect on the patient, for example by sucking breath away too rapidly. The active part of the scavenging apparatus that is connected to the breathing system is known as the receiving system, and it is this part that should comply with the abovementioned criteria. Guidelines for the design and performance criteria of receiving systems are laid down in BS 6834. However in practice it is difficult to design apparatus meeting the guidelines set down by that standard especially in terms of inlet suction and noise emission.

The present invention is directed at providing an active gas scavenging receiving system that does not provide excessive suction on the patient breathing system.

According to the present invention there is provided gas scavenging apparatus for connection to a patient breathing system comprising a hollow receiver body through which a flow of air is drawn in a first direction from a first end open to the atmosphere to a second end connected to a disposal system, and an inlet from the patient breathing sytstem, said inlet communicating with the receiver body and having an increased cross-section opening facing the flow disposed so that the flow passes externally around the opening and creates a suction within the inlet.

The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 is a perspective, exploded view of an embodiment of the invention; and Figure 2 is a schematic outline of the inner components of the embodiment of Figure 1.

An active gas scavenging system may comprise three parts: a transfer system which connects the scavenging system to the exhaust port of the patient breathing system, a receiving system which receives gases from the transfer system or which may be connected directly to the breathing system (i.e. eliminating or incorporating the receiving system) and a disposal system which conveys the scavenged gases to a safe discharge location such as outside the buildings.

In Figure 1, a preferred form of gas scavenging receiving system is shown comprising a tubular receiver body l made for example of an aluminium tube of external diameter 76 mm and internal diameter 63.5 mm. At one end of the receiver body there is a flared portion 2 with a protective grille 3 over the open end of the flared portion. Close to the other end of the receiver body 1 there is an aperture through which a standard 30mm patient inlet 4 extends. This patient inlet is connected to a patient body port 5 located within the receiver body 1; this port is shown in Figure 2. The end of the receiver body remote from the flared portion, referred to hereinafter as the patient inlet end, has a screw thread that engages with a corresponding thread on a transparent indicator housing 6.The indicator housing 6 may for example comprise a transparent plastic tube. Above (as viewed) the indicator housing, a flanged filter mesh 7 locates between the indicator housing 6 and an end piece connector 8 which has a connection port 9 for connection to the disposal system and through which air is sucked from the open flared end of the receiver body up through the receiver body 1.

A spindle 10, which screws into the patient body port S extends out of the patient inlet end of the receiver body 1 and has a piston 11 slidably mounted thereon. The piston has a diameter less than that of the indicator housing so that there is a relatively free passage for air through the receiver tube 1, around the piston circumference, through the filter and into the disposal system. When the apparatus is assembled air is sucked through the receiver tube 1 at a preferred rate of less than or equal to 130 litres per minute, which is the maximum rate permitted at the connection to the disposal system in BS 6834. A suitable range is 60 to 130 litres per minute. A valve may be incorporated into the end piece connector to limit the flow rate.The movement of air through the receiver tube and indicator housing urges the piston 11 upwardly (as viewed) away from the patient inlet end of the receiver body 1, and the position of the piston can be viewed through the indicator housing. If the flow rate falls below 130 litres per minute the piston 11 falls down the spindle closer to the patient inlet end of the receiver tube. (The assembly is intended to be mounted substantially upright with the end piece 8 uppermost). A flow rate calibration on the indicator housing enables the flow rate to be monitored by viewing the piston position.

Referring now also to Figure 2, within the receiver body 1 a patient inlet body 5 is located, supported in position by engagement with the patient inlet 4 at the aperture in the receiver body. The patient inlet body comprises a substantially tubular L-shaped member connecting to the spindle 10 (without an airway) and to a patient funnel 12, there being a free airway from the patient inlet 4 through the patient body 5 and patient funnel 12.

The patient funnel 12 has a tubular mouth portion 13 and conical portion 14 and is dimensioned so that when air is sucked through the receiver tube at a rate of 130 litres per minute a Venturi proximate the mouth of the funnel provides suction of gases from the patient inlet tube, through the patient body 5, through the funnel 12 into the receiver tube 1 and thenceaway to the disposal system. The suction flow rate is limited to a maximum of 0.5 litres per minute with a receiver tube flow of 130 litres per minute. This can be achieved with the receiver tube dimensions previously given with a length of 383 millimetres from the flared end of the receiver tube to the mid point of the patient inlet, and with the other related dimensions as follows: Funnel 12: inside diameter 52 mm outside diameter 55 mm mouth portion length 32.5 mm conical portion taper 42 conical portion length 12.5 mm inside diameter at connection to body 5 26 mm overall length 53 mm overlap with body 5 mm Body 5: funnel connection to patient inlet mid point 20.5 mm Other dimensions are shown on Figure 2 of the drawings in millimetres.

Claims

1. Gas scavenging apparatus for connection to a patient breathing system comprising a hollow receiver body through which a flow of air is drawn in a first direction from a first end open to the atmosphere to a second end connected to a disposal system, and an inlet from the patient breathing system, said inlet communicating with the receiver body and having an increased cross-section opening facing the flow disposed so that the flow passes externally around the opening and creates a suction within the inlet.

2. Gas scavenging apparatus acco#rding to claim 1 having an air flow rate indicator means attached to the second end of said receiver body, said indicator means comprising a tubular transparent casing, and a spindle coaxial with the casing supporting a piston which is free to move in response to the air flow from the receiver body.

3. Gas scavenging apparatus according to claim 2 wherein said transparent casing is marked with a flow rate calibration.

4. Gas scavenging apparatus according to claims 2 or 3 wherein a filter mesh is located between the indicator means and the disposal system.

5. Gas scavenging apparatus according to any preceding claim wherein the first end of the receiver body is flared and is covered by a protective grille.

6. Gas scavenging apparatus according to any preceding claim wherein a valve is used to limit the air flow rate.

7. Gas scavenging apparatus according to any preceding claim wherein the suction within the inlet causes a suction flow from the patient breathing system.

8. Gas scavenging apparatus according to claim 7 wherein the suction flow rate is a maximum of 0.5 litres per minute, the air flow rate is in the range of 60 to 130 litres per minute, the receiver body has an internal diameter in the range 58 to 69 mm, the inlet has an internal diameter in the range 20 to 30 mm and the inlet opening has an internal diameter in the range 50 to 60 mm.

9. Gas scavenging apparatus according to claim 8 wherein the air flow rate is 130 litres per minute, the receiver body has an internal diameter of 63.5 mm, the inlet has an internal diameter of 26 mm, and the inlet opening has an internal diameter of 52 mm.