Surgery – Respiratory method or device – Means for mixing treating agent with respiratory gas
Reexamination Certificate
1999-03-03
2001-04-24
Ruhl, Dennis (Department: 3761)
Surgery
Respiratory method or device
Means for mixing treating agent with respiratory gas
C128S204220, C128S204210, C128S205240, C261S026000, C261S028000
Reexamination Certificate
active
06220242
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dosing device and in particular to a dosing device suitable for use in an anaesthesia machine or ventilator to regulate the concentration of a liquid vapor, such as an anaesthetic vapor, in a carrier gas component of a breathing gas.
2. Description of the Prior Art
It is common to administer liquid anaesthetic agents to a patient as a gas. This is done by vaporizing the liquid and then conducting the vaporized anaesthetic to the patient in a carrier gas. It is important that the amount of anaesthetic agent is accurately controlled and this is generally achieved in one of two ways; either by controlling the flow rate of the carrier gas through a reservoir of liquid anaesthetic or by controlling the dose of liquid anaesthetic to be supplied for vaporization. If a fault occurs in a device operating in the first way then relatively high doses can be taken from the reservoir. Even if other security measures for the patient are provided and are triggered, the patient may still be exposed to a quantity that could cause discomfort, and in the worst case even a harmful or lethal quantity.
A known dosing device for controlling the dose of liquid anaesthetic to be supplied for vaporization is described in WO 92/19303 (BOC Group PLC) and has a variable volume pump which can be operated to define the dose to be supplied by varying the volume in a controlled manner using a stepper motor. This device, however, requires that the pump and stepper motor are manufactured to a high mechanical tolerance, which adds to the cost of such a device as well as to the manufacturing difficulties. Additionally the generation of an intermittent flow, particularly of low flow rate, may be problematic since this requires accurate control of the pump volume over the majority of its stroke length.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a dosing device in which the need for metering variations of pump volume is avoided.
This is achieved by a dosing device according to the invention wherein the flow of the liquid to be vaporized is monitored directly using a flow meter, the output of which operates a flow control component, for example a variable flow restriction, to regulate the supply of one or both of the liquid and carrier gas. Thus the need to determine and control exact pump chamber volume changes is removed and the dose may be supplied using a less sophisticated and relatively inexpensive over-pressure and on off valve arrangement.
Moreover, as flow control may be more readily achieved than volume control and as the supply is directly controlled from the actual liquid flow a controllable intermittent dose can be more readily achieved.
Preferably the flow meter has a pressure sensor adapted to provide a measure of the flow from the pressure exerted by incident liquid. Such a sensor is much better suited to the measurement of the relatively small flows that may be present in the dosing device than, for example, resistance type flow meters. Moreover, such a pressure sensor may be readily constructed, using current technology, to present little obstruction to the overall fluid flow path.
The dosing device can have a guide component, such as a capillary tube, for directing substantially all of the flowing liquid to the flow meter. This has the advantage, particularly at low doses, that the signal from the flow meter is a direct measure of the total amount of flowing liquid. Moreover, the capillary tube, because of its dimensions, may provide a substantially laminar liquid flow to the sensor. Thus a more accurate flow measurement may be made since the flow characteristics are more predictable.
REFERENCES:
patent: 4038980 (1977-08-01), Fodor
patent: 5235971 (1993-08-01), Falb et al.
patent: 5237990 (1993-08-01), Psaros et al.
patent: 5243973 (1993-09-01), Falb et al.
patent: 5509406 (1996-04-01), Kock et al.
patent: 5771882 (1998-06-01), Psaros et al.
patent: 0 545 567 (1993-06-01), None
patent: WO 92/19303 (1992-11-01), None
Patel Mital
Ruhl Dennis
Schiff & Hardin & Waite
Siemens-Elema AB
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