Method and apparatus for facilitating delivery of anaesthetic

Abstract

The present invention relates to a method and apparatus for facilitating anaesthesia, particularly in Re-Breather anaesthetic circuits. A problem with Re-Breather circuits is that their dynamic response can be relatively slow. The dynamic response is the response of the circuit to delivering changes of anaesthetic concentration. In current circuits, Fresh Gas containing anaesthetic is delivered into the circuit and may be substantially diluted by the gas already present in the circuit. It is therefore difficult to achieve a rapid increase of anaesthetic concentration for delivery to the patient. In the present invention, an accumulator is placed in the Re-Breather circuit to accumulate Fresh Gas containing anaesthetic as it is introduced into the circuit, adjacent an inhalation conduit to the patient. Fresh Gas containing high concentrations of anaesthetic is therefore immediately available to the patient.

1 . A conservation arrangement for an anaesthetic apparatus including an accumulator configured to be positioned, in use with the conservation arrangement connected in the anaesthetic apparatus, between an inhalation part of the anaesthetic apparatus and other downstream components of the anaesthetic apparatus, inhalation part of the anaesthetic apparatus having an inhalation port and a fresh gas inlet, so that Fresh Gas entering the anaesthetic apparatus must flow from the inhalation part through the accumulator to the other downstream components of the anaesthetic apparatus before being diluted with gas already contained in the other downstream components of the anaesthetic apparatus, and gas already contained in the other downstream components of the anaesthetic apparatus must pass through the accumulator arrangement to reach the inhalation part, the conservation arrangement being arranged to conserve the fresh gas entering the anaesthetic circuit proximate the inhalation port for delivery undiluted or predominantly undiluted to the patient on inhalation and slow mixing of the fresh gas entering the anaesthetic apparatus, with gas already contained in the anaesthetic apparatus downstream components. 
     
     
         2 . The conservation arrangement of  claim 1 , wherein in use with the conservation arrangement connected in the anaesthetic apparatus the accumulator is positioned immediately adjacent the inhalation port and arranged to accumulate fresh gas entering the anaesthetic apparatus. 
     
     
         3 . The conservation arrangement of  claim 1 , wherein the accumulator has a geometry arranged to reduce flow of fresh gas away from the inhalation port to reduce mixing of the fresh gas in the accumulator with gas already contained in the anaesthetic apparatus. 
     
     
         4 . The conservation arrangement of  claim 3 , wherein the accumulator comprises an elongate accumulator passage of relatively small cross-sectional area as compared with the cross-sectional areas of passageways in the rest of the anaesthetic apparatus. 
     
     
         5 . The conservation arrangement of  claim 4 , wherein the elongate accumulator passage has a cross-sectional area that is 50% or less than that of the minimum cross-sectional area in the rest of the anaesthetic apparatus. 
     
     
         6 . The conservation arrangement of  claim 4 , wherein the accumulator comprises a plurality of the elongate accumulator passages, the plurality of passages arranged to receive and accumulate the fresh gas. 
     
     
         7 . The conservation arrangement of  claim 6 , wherein the plurality of accumulator passages have a combined cross-sectional area which is 50% or less than the minimum cross-sectional area of the rest of the anaesthetic apparatus. 
     
     
         8 . The conservation arrangement of  claim 1 , wherein the accumulator has a proximal end arranged to be positioned, in use when the conservation arrangement is connected in an anaesthetic circuit, proximate a fresh gas inlet of the anaesthetic circuit to receive and accumulate the fresh gas entering the anaesthetic circuit, and proximate an inspiration arm of the anaesthetic circuit to deliver the Fresh Gas accumulated in the accumulator directly to the inspiration arm with minimal dilution, and a distal end having an outlet to the other downstream components of the anaesthetic circuit. 
     
     
         9 . The conservation arrangement of  claim 1 , wherein the volume of the accumulator is arranged to be of the same order of magnitude as the tidal volume of a patient to be anaesthetized using the anaesthetic apparatus. 
     
     
         10 . The conservation arrangement of  claim 1 , further comprising a housing comprising ports and passageways arranged to connect the conservation arrangement to other components of the anaesthetic apparatus. 
     
     
         11 . The conservation arrangement of  claim 10 , wherein the ports and passageways of the housing are arranged to connect other components of the anaesthetic apparatus in positions which optimise the operation of the conservation arrangement. 
     
     
         12 . The conservation arrangement of  claim 10 , wherein the ports and passageways comprise a pressure relief valve port arranged to connect to a pressure release valve, whereby the pressure release valve port is, in operation, at a position in the anaesthetic apparatus where the concentration of the anaesthetic is the lowest. 
     
     
         13 . The conservation arrangement of  claim 12 , further comprising a valve manifold, arranged to mount an exhalation valve so that an outlet of the exhalation valve opens into a port connected to the pressure release valve port. 
     
     
         14 . The conservation arrangement of  claim 13 , wherein the valve manifold mounting an inhalation valve, an inlet of the inhalation valve being arranged proximate a fresh gas inlet of the housing. 
     
     
         15 . (canceled) 
     
     
         16 . (canceled) 
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . A conservation arrangement, arranged for an anaesthetic apparatus comprising:
 a housing, having a fresh gas port for receiving fresh gas from a vaporizer, an inhalation port for providing gas to an inhalation conduit for a patient, an accumulator, a container for containing carbon dioxide absorbent and an exhalation port for receiving expired gas from a patient, and forming a fluid communication path between the inhalation conduit and exhalation port via the accumulator and container for containing carbon dioxide absorbent, such that expelled breath gas flows from the exhalation port, through the container for containing carbon dioxide and accumulator back toward the fresh gas port and inhalation port to mix with fresh gas for inhalation by the patient,   a proximal end of the accumulator being located proximate the inhalation port and fresh gas port to provide the fluid communication path to the container for containing carbon dioxide absorbent and whereby gas from the exhalation port and canister must flow through the accumulator to the inhalation port, the accumulator being arranged to conserve fresh gas entering the apparatus proximate the inhalation port for delivery undiluted or predominantly undiluted to the patient on inhalation and slow mixing of the fresh gas with the gas in the rest of the apparatus.   
     
     
         20 . The conservation arrangement of  claim 19  wherein the housing further includes a reservoir port for attachment of a compliant reservoir for absorbing pressure fluctuations within the anaesthetic apparatus, the reservoir port being arranged to connect the reservoir in the fluid communication path between the exhalation port and the container for containing carbon dioxide absorbent. 
     
     
         21 . The conservation arrangement of  claim 1  wherein the volume of the accumulator is equal to or greater than one quarter of a tidal volume of a smallest patient for which the anaesthetic apparatus is to be used. 
     
     
         22 . The conservation arrangement of  claim 8  further comprising a canister arranged to contain a carbon dioxide absorbent, comprising an outlet and an inlet, the outlet being arranged to be positioned towards the distal end of the accumulator. 
     
     
         23 . The conservation arrangement of  claim 22  wherein the inlet and outlet are arranged so that gas flow through the canister is unidirectional from one end of the canister to the other, and from a central part of the canister to the outside of the canister. 
     
     
         24 . The conservation arrangement of  claim 22  further comprising a fitting arranged to connect to a breathing bag for the anaesthetic circuit, the fitting being arranged to be connected proximate the inlet end of the canister, and to receive gas from the expiration side of the apparatus for subsequent flow through the canister.