Methods for compensating for pressure differences across valves in IV pumps
View Patent ↗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.
1. A method for minimizing an error in a disposable cassette pump used for infusing a fluid into a patient, comprising the steps of:
(a) sensing an inlet pressure of the cassette pump during a pump cycle;
(b) sensing an outlet pressure of the cassette pump during the pump cycle;
(c) determining a differential pressure between the inlet pressure and the outlet pressure;
(d) using the differential pressure, determining a compensation pressure that should be applied to the fluid in the cassette pump before infusing the fluid into the patient; and
(e) applying the compensation pressure to the fluid in the cassette pump before infusing the fluid into the patient.
2. The method of claim 1 , wherein the fluid is displaced from the cassette pump by a driven member, the step of applying the pressure compensation comprising the step of adjusting a position of the driven member relative to the cassette pump.
3. The method of claim 1 , further comprising the steps of:
(a) sensing a pressure associated with the outlet port of the cassette pump when the fluid is being delivered to the patient;
(b) determining a correction factor for a calibration difference between an inlet pressure sensor and an outlet pressure sensor used to sense the inlet pressure and the outlet pressure; and
(c) applying the correction factor for the calibration difference to one of the inlet and outlet pressures sensed in a next pump cycle.
4. The method of claim 1 , further comprising the steps of:
(a) determining an actual volume of fluid delivered in a current pump cycle;
(b) determining a change in a duration of a delivery interval of the cassette pump that is required to compensate for any differences between the actual volume of fluid delivered and desired volume of fluid to be delivered; and
(c) applying the change in the duration of the delivery interval in the next pump cycle.
5. A method for minimizing an error in an infusion pump used for infusing a fluid into a patient, comprising the steps of:
(a) sensing a first pressure within a pumping chamber of the pump during a first part of a pump cycle;
(b) sensing a second pressure within a pumping chamber of the cassette pump during a second part of a pump cycle;
(c) determining a differential pressure between the first pressure and the second pressure;
(d) using the differential pressure, determining a compensation pressure that should be applied to the fluid in the chamber before infusing the fluid into the patient; and
(e) applying the compensation pressure to the fluid in the chamber before infusing the fluid into the patient.