Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Reexamination Certificate
1999-08-25
2001-10-09
Lewis, Aaron J. (Department: 3761)
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
C128S203140, C128S203240, C128S203250
Reexamination Certificate
active
06298845
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a vaporizer, particularly for vaporizing a liquid anaesthetic, of the type having an inlet for a carrier gas, an outlet for the carrier gas and vaporized anaesthetic, a flow channel connecting the inlet and the outlet, a chamber for the liquid anaesthetic, a first connection between the flow channel and the chamber, a second connection between the flow channel and the chamber downstream from the first connection, and a throttle in the flow channel between the first and second connections.
2. Description of the Prior Art
The manual “Halothane Vaporizer 950, Enflurane Vaporizer 951, Isoflurane Vaporizer 952”, Siemens-Elema AB, January 1988, contains a description of a vaporizer of the above general type. The vaporizer has a gas flow passage for a gas, a chamber for liquid anaesthetic and an adjustable throttle. An opening between the gas flow passage and the chamber is situated upstream from the adjustable throttle. A capillary tube with a nozzle in the gas flow passage and its other end immersed in the liquid anaesthetic in the chamber is arranged downstream from the adjustable throttle.
The presence of a gas flow generates a pressure drop across 20 the adjustable throttle. The higher pressure upstream from the throttle is propagated through the opening in the chamber and exerts pressure on the surface of the liquid, thereby forcing the liquid up through the capillary tube. The liquid is then injected through the nozzle into the gas flow passage and is vaporized.
The pressure drop across the throttle depends on the throttle's setting and controls the dispensing of liquid. Different concentrations of anaesthetic can be achieved by changing the throttle's setting.
The known vaporizer has an accuracy of ±0% of the value set. This is sufficient for all applications in conjunction with anaesthesia. However, this known vaporizer has certain disadvantages.
One disadvantage is that the vaporizer is not suitable for liquids with a boiling point close to the ambient temperature. Desflurane is one such liquid and has a boiling point of about 22° C. at normal atmospheric pressure.
Another disadvantage is that the vaporizer's operating pressure must first be reached each time a flow of gas is sent to the vaporizer for dispensing anaesthetic. This creates a small but measurable dispensing delay. Also, the chamber must first fill with gas before the pressure can act on the surface of the liquid. Moreover, a small amount of gas is lost when the chamber only contains a small amount of liquid. This subsequently has some effect on the concentration of dispensed anaesthetic.
Although these disadvantages only have a slight and virtually insignificant impact on vaporizer function, additional refinement of this function would still be desirable.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a vaporizer which avoids the aforementioned problems.
The above object is achieved in accordance with the principles of the present invention in a vaporizer of the type initially described, wherein the second connection is formed as a conduit having one end immersed in the liquid anaesthetic, and a valve connected to the other end of the conduit, the valve being designed to open when a predetermined drop in pressure develops across the throttle, thereby allowing liquid anaesthetic to be dispensed into the flow channel.
The second connection between the chamber and the flow channel is devised with a conduit for liquid in the chamber and a valve which opens the conduit to the flow channel when the pressure drop across the throttle exceeds a preset value.
The conduit can be a capillary tube, as described above, but other conduits are possible. The conduit can be devised with a nozzle that atomizes the liquid when it is injected into the flow channel. This facilitates vaporization of the liquid.
The throttle can be adjustable in order to affect the drop in pressure, or the throttle can be fixed and an adjustable outlet valve can be arranged to regulate the drop in pressure.
The first connection can be open with most liquids, as in the prior art. Arranging a pre-biased check valve in the first connection, however, is advantageous for liquids with a low boiling point. In this manner, a higher pressure can be maintained in the chamber, thereby raising the boiling point. A pressure increase of 1 bar raises the boiling point of desflurane to about 28° C.
In the latter instance, the pressure drop must not be allowed to reach the opening pressure of the valve until the pressure in the flow channel exceeds the pressure in the chamber.
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Halothane Vaporizer 950, Enflurane Vaporizer 951, Isoflurane Vaporizer 952 Operating Manual, Siemens-Elema AB, Jan. 1988.
Emtell Par
Hoglund Kasper
Lewis Aaron J.
Schiff & Hardin & Waite
Siemens Elema AB
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