Method for compensating for pressure differences across valves in cassette type IV pump

• US 7,402,154 B2
• Filed: 06/21/2005
• Issued: 07/22/2008
• Est. Priority Date: 12/17/1999
• Status: Expired due to Term

• Current Assignee: ICU Medical Incorporated
• Original Assignee: Hospira Incorporated (Pfizer Inc.)
• Inventors: Maske, Rudolph J., Holst, Peter A., Krajewski, David A.
• Primary Examiner(s): Mendez; Manuel A
• Application Number:
  US11/157,758
• Publication Number:
  US 20050235733A1
• Time in Patent Office: 1,127 Days
• Field of Search: 604/65, 604/66, 604/67, 604/153, 604/151, 128/12, 128/13
• US Class Current: 604/153
• CPC Class Codes: A61M 2205/12 with interchangeable cassettes forming partially or totally the fluid circuit
• CPC Class Codes: A61M 2205/3355 Controlling downstream pump pressure
• CPC Class Codes: A61M 2205/50 with microprocessors or computers
• CPC Class Codes: A61M 5/14224 Diaphragm type
• CPC Class Codes: A61M 5/16809 by repeated filling and emptying of an intermediate volume pressure infusion using positive displacement pumps A61M5/142
• CPC Class Codes: A61M 5/16827 controlling delivery of multiple fluids, e.g. sequencing, mixing or via separate flow-paths infusion of multiple fluids without using a controller A61M5/1407
• CPC Class Codes: A61M 5/365 Air detectors A61M5/1684 takes precedence; in extracorporeal blood circuits A61M1/3626
• CPC Class Codes: G05D 16/2046 the plurality of throttling means being arranged for the control of a single pressure from a plurality of converging pressures G05D16/204 takes precedence

Abstract

A pump used to infuse a fluid into a patient is controlled in accordance with an algorithm that enables a microprocessor to monitor and adjust each pump cycle to compensate for a differential pressure between the pump'"'"'s inlet and outlet. The algorithm defines a fluid delivery protocol that is applied in controlling the operation of the pump to achieve a desired rate, volume, and timing of the fluid infusion. Fluid is delivered by the pump when a plunger compresses an elastomeric membrane overlying a fluid chamber. Due to the small volume of the chamber, an incremental change in the plunger position before the delivery stroke produces a significant change in the delivery pressure. At the beginning of a pump cycle, the microprocessor determines the differential pressure between the inlet and outlet of the pump, and adjusts the plunger position before the delivery stroke to compensate for the differential pressure. A retraction of the plunger from the home position decreases the delivery pressure of the fluid, and an advancement of the plunger increases it. After the position of the plunger is adjusted to compensate for the differential pressure, the pump cycle proceeds. Following the plunger stroke, the outlet pressure is used to determine the actual volume of fluid delivered. The duration of the plunger stroke in the next pump cycle is adjusted to compensate for any volume delivery error produced by the differential pressure compensation.

Claims

1. A method for determining a difference in a calibration between an inlet pressure sensor and an outlet pressure sensor in an infusion pump for infusing a fluid into a patient, comprising the steps of:

(a) providing a cassette having a housing that defines a fluid path between an inlet port adapted to couple in fluid communication with the source and an outlet port adapted to couple in fluid communication with an infusion site on the patient, said cassette including an inlet pressure sensor that produces a signal indicative of a pressure proximate the inlet port, and an outlet pressure sensor that produces a signal indicative of a pressure proximate the outlet port, said fluid path including;

(i) a chamber covered by an elastomeric membrane that when forced into the chamber, displaces the fluid from the chamber through the outlet port;

(ii) an inlet valve controlling a flow of the fluid into the chamber from the inlet port, said inlet valve being open as the fluid flows into the chamber from the inlet port and closed as the fluid is displaced through the outlet port; and

(iii) an outlet valve controlling a flow of the fluid from the chamber toward the outlet port, said outlet valve being open when the fluid is displaced through the outlet port and closed as the fluid flows into the chamber from the inlet port;

(b) opening the inlet valve while the outlet valve is closed, thus filling the chamber with fluid, and closing the inlet valve when the chamber is filled with a desired volume of fluid;

(c) determining a pressure proximate the inlet port and a pressure proximate the outlet port using the inlet and outlet pressure sensors;

(d) adjusting a position of the elastomeric membrane such that a pressure of the fluid within the chamber is equivalent to the pressure proximate the outlet port; and

(e) opening the outlet valve, and using the outlet pressure sensor, determining if a pressure spike accompanies the opening of the outlet valve, said pressure spike being indicative of a calibration difference between the inlet pressure sensor and the outlet pressure sensor.