Patent ID: 8475138

Claim:
A self-adjusting fluid pump for circulating fluid through an extracorporeal path, comprising: (a) a piston pump containing at least one piston and piston motor, said piston including a pressure sensor; (b) a flexible cassette with at least one fluid input containing one or more fluids, adjacent to said piston, wherein advancing the piston causes said one or more fluids to flow from the cassette to a patient and wherein said cassette has a plurality of inlet valves that communicate with a first and second pumping chamber; (c) a processing means for using data from the piston pressure sensor to calculate the rate of fluid input flow into each respective pumping chamber for each pump cycle, and to calculate an output flow rate based upon the input flow rate; a second fluid input is coupled to the cassette to infuse a calculated volume for supporting the calculated output flow rate to maintain a patient's arterial blood pressure within a prescribed range; wherein said processing means is configured to compare said calculated output flow rate from part (c) to a pre-specified target output flow rate; and said processing means is configured to implement a filling protocol into said first pumping chamber in parallel to the expulsion of said one or more fluids from said second pumping chamber, said filling protocol further comprising: (1) synchronizing the plurality of inlet valves to introduce a first fluid into said first pumping chamber by retracting said piston motor a predefined amount to admit a volumetric quantity of the first fluid relative to the total volume of said first pumping chamber; (2) testing the volumetric accuracy of the first fluid within said first pumping chamber by occluding an inlet path to said first pumping chamber, advancing said piston motor to increase the pressure within said first pumping chamber to a predetermined level, and determining whether a sufficient quantity of the first fluid was delivered to said first pumping chamber based on the relative position of said piston and the measured pressure in said first pumping chamber; (3) synchronizing the plurality of inlet valves to introduce a second fluid into said first pumping chamber; and (4) testing the volumetric accuracy of the total volume of fluid within said pumping chamber by occluding the inlet path to said first pumping chamber, advancing said piston motor to increase the pressure within said first pumping chamber to a predetermined level, and determining whether a sufficient quantity of first and second fluids was delivered to said first pumping chamber based on the relative position of said piston and the measured pressure in said first pumping chamber.