Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Patent
1993-03-25
1994-12-13
Page, Thurman K.
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
12820313, 12820414, 12820417, 12820011, 12820326, 12820327, A61M 1100, A61M 1600
Patent
active
053721276
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a sump for an anaesthetic agent vaporiser, and to a method of vaporising an anaesthetic agent. A known vaporiser for volatile anaesthetic agents Includes a vaporising chamber for liquid anaesthetic agent, and an inlet into the vaporising chamber for a carrier gas which entrains anaesthetic agent vapor within the chamber above the surface of the liquid anaesthetic agent and carries the vapor out of the vaporiser for adminstration to a patient. Such a vaporiser is disclosed in GB-1224478.
The vapor pressure of many volatile anaesthetic agents is heavily dependent on the ambient temperature at which the vaporiser operates. In order to minimise the dependence of vapour pressure on the ambient temperature in which the vaporiser operates, it is known to provide a heater within the vaporising chamber by which the temperature of anaesthetic agent within the chamber can be controlled. It is to be understood however that the temperature of the anaesthetic agent is maintained significantly below its boiling point; anaesthetic agent vapour is therefore carried out of the vaporising chamber not under its own vapour pressure, but entrained in the carrier gas which is supplied to the chamber.
A recently introduced anaesthetic agent, 2-(difluoromethoxy)-1,1,1,2-tetrafluoroethane has a relatively low boiling point in the region of ambient temperature. Conventional techniques for administration of anaesthetic agents having boiling points well above ambient temperature, using vaporisers such as that disclosed in GB-1224478, are not generally applicable to this new agent. Recently developed vaporisers for low boiling point anaesthetic agents are disclosed in EP-A-438218 and European patent application no. 91306823.5. Subject matter disclosed In those documents is incorporated in this specification by these references to the documents. A vaporiser includes a vaporising chamber for liquid anaesthetic agent, in which the agent is vaporised. The vaporiser further includes a passage which extends from an inlet for carrier gas to an outlet. Anaesthetic agent vapour from the vaporising chamber flows from the chamber under the pressure which is generated as a result of the liquid agent having been heated to cause it to boil, to mix with carrier gas in the passage so that the carrier gas which is discharged from the outlet, for administration to a patient, is a mixture of carrier gas and anaesthetic: agent vapour.
SUMMARY OF THE INVENTION
In vaporisers for low boiling point vaporisers, it is particularly important that the temperature of the liquid anaesthetic agent within the vaporising chamber be controlled carefully, because the pressure of the anaesthetic agent vapour is so heavily dependent on the temperature of the liquid anaesthetic agent relative to its boiling point. It can also be desired in many instances to reach the controlled temperature of the liquid anaesthetic agent as quickly as possible after replenishing the supply of agent to the vaporising chamber or after first turning on the vaporiser.
The present invention provides a sump for an anaesthetic vaporiser, which includes a partition member located in the vaporising chamber by which a portion of the liquid anaesthetic agent can be entrapped, for heating by means of an associated heater.
Accordingly, the invention provides a sump for an anaesthetic agent vaporiser, which comprises: vaporising chamber and cooperates with the internal wall of the vaporising chamber to entrap a portion of liquid anaesthetic agent at a location immediately adjacent the heater, the plate having a partition outlet at a position above the maximum level of liquid anaesthetic agent within the space defined by the partition member and the internal wall of the vaporising chamber, through which anaesthetic agent vapour can pass through the plate.
The sump of the invention has the advantage that a quantity of liquid anaesthetic agent can be heated rapidly to a desired temperature, which is above the boiling point of the anaesthetic agent, so that a pressure of anaesth
REFERENCES:
patent: 3219795 (1962-03-01), Wiseman
patent: 3319046 (1967-05-01), Katzman
patent: 4607634 (1986-08-01), Clapham
Sampson David C.
Thwaites David J.
Bawa Raj
Cassett Larry R.
Page Thurman K.
Rathbun Roger N.
The BOC Group plc
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