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

• US 6,942,636 B2
• Filed: 10/29/2002
• Issued: 09/13/2005
• 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:
  US10/282,967
• Publication Number:
  US 20030055375A1
• Time in Patent Office: 1,050 Days
• Field of Search: 604 20- 22, 604/19, 604/890.1, 604/289, 604/291, 604/304, 604/500, 604/501, 604/503
• US Class Current: 604/19
• 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 system for maintaining a desired delivery rate of a fluid flow through an intravenous line, comprising:

(a) a pump chassis;

(b) a pump in fluid communication with the intravenous line and mountable within the pump chassis to receive a driving force from a driven member, said pump including an inlet port, an outlet port, an elastomeric membrane overlying a chamber comprising a portion of a fluid path extending between the inlet port and outlet port, said driven member exerting a force on the elastomeric membrane that displaces the fluid from the chamber and into the intravenous line;

(c) an inlet pressure sensor that produces an inlet pressure signal indicative of an inlet pressure upstream of the chamber;

(d) an outlet pressure sensor that produces an outlet pressure signal indicative of an outlet pressure downstream of the chamber; and

(e) a controller that is electrically coupled to the inlet pressure sensor and the outlet pressure sensor to receive the inlet and the outlet pressure signals, said controller employing the inlet pressure signal and the outlet pressure signal to determine a first correction factor to be applied to an initial position of the driven member, said first correction factor being expressed as a change in a position of the driven member relative to the chamber.

2. The system of claim 1, wherein when the first correction factor requires the driven member to be advanced toward the chamber, a pressure at which the fluid is released from the outlet port is increased;

and wherein when the first correction factor requires the driven member to be retracted away from the chamber, the pressure at which the fluid is released from the outlet port is decreased.

3. The system of claim 1, wherein the first correction factor is applied to change the position the driven member relative to the chamber at the beginning of each pump cycle.

4. The system of claim 1, wherein the controller monitors the outlet pressure signal to determine a pressure spike associated with the release of fluid from the outlet port and determines a second correction factor to be applied to the inlet pressure signal to correct for any calibration difference between the inlet port and the outlet port pressure sensors.

5. The system of claim 1, wherein the controller uses the inlet pressure signal and the outlet pressure signal to determine an actual volume of fluid delivered during each pump cycle, and determines a third correction factor to be applied to a duration of a delivery stroke in the next pump cycle, to compensate for a difference between the actual volume of the fluid delivered and a target volume.

6. The system of claim 1, wherein the controller further comprises a processor and a memory, and the memory stores a plurality machine instructions that cause the processor to perform a plurality of logical steps when the machine instructions are executed by the processor, said logical steps including:

(a) sampling the inlet pressure signal produced by the inlet pressure sensor, and the outlet pressure signal produced by the outlet pressure sensor during each pump cycle to determine said first correction factor, and applying the first correction factor during the current pump cycle,

(b) sampling the inlet pressure signal produced by the inlet pressure sensor and the outlet pressure signal produced by the outlet pressure sensor as the fluid is released from the outlet port, to determine a second correction factor, said second correction factor correcting for a calibration difference between said inlet and outlet pressure sensors, and applying the second correction factor to the inlet pressure signal during the next pump cycle, and

(c) sampling the inlet pressure signal produced by the inlet pressure sensor and the outlet pressure signal produced by the outlet pressure sensor after the fluid is released from the outlet port to determine a third correction factor, said third correction factor adjusting a duration of a pump delivery stroke, and applying the third correction factor during the next pump cycle.

7. The system of claim 1, wherein a plurality of samples are averaged to minimize an effect of variations in pressure, individual samples being taken during one of a predefined interval of time and a duration of a step of a prime mover that is providing the driving force.