Importance

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Abstract

Patient controlled analgesic (PCA) infusion apparatus and method are disclosed, in which a liquid desired to be self-infused into a patient is controllably supplied from a positively pressurized supply reservoir to a lower pressure dose chamber of a patient operable syringe from which the patient may expel the liquid and infuse such into a suitable infusion site, as through a cannula inserted into the patient, the supply of liquid from the reservoir to the dose chamber being controlled by a flow control metering tube assembly, including a connecting tube with a flow-restricting metering rod disposed therein and of a selected effective length such that the combined flow impedance of the flow path formed by the overall flow metering tube and rod provide a selected flow rate for a reference fluid and reference pressure differential. The flow control metering tube assembly may be suitably constructed by empirical testing and sizing of individual flow control tube/rod assemblies to achieve a desired flow impedance. A suction, preferrably forming a vacuum-induced void, is automatically effected in the dose chamber by a return spring acting on a piston forming a rear wall of the dose chamber, after each infusion by the patient, so as to effect a desired selected substantially constant refill flow rate of liquid from the supply reservoir and into the dose chamber. A check valve is provided in an outlet tube to enable patient actuated infusion outflow of liquid from the dose chamber while opposing reverse inflow back into the dose chamber, and thus aiding in enabling a desired suction vacuum induced void to be created within the dose chamber during the dose chamber refill operation as a function of fast rearward spring acting return movement of a piston forming the movable rear wall of the dose chamber.

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First Claim