AIR DETECTION SYSTEM AND METHOD FOR DETECTING AIR IN A PUMP OF AN INFUSION SYSTEM

• US 20130261993A1
• Filed: 03/27/2013
• Published: 10/03/2013
• Est. Priority Date: 03/30/2012
• Status: Active Grant

• Current Assignee: ICU Medical Incorporated
• Original Assignee: ICU Medical Incorporated
• Inventors: Ruchti, Timothy L., Markey, Brian G., Belkin, Anatoly S., Kotnik, Paul T., Khair, Mohammed M.
• Granted Patent: US 9,995,611 B2
• Time in Patent Office: Days
• US Class Current: 702/50
• CPC Class Codes: A61M 2205/331 used as turbidity change detectors, e.g. for priming-blood or plasma-hemoglubine-interface detection
• CPC Class Codes: A61M 5/16831 Monitoring, detecting, signalling or eliminating infusion flow anomalies low-level float-valves causing cut-off A61M5/40; indicating or recording presence, absence or direction of flow in general G01P13/0066
• CPC Class Codes: A61M 5/365 Air detectors A61M5/1684 takes precedence; in extracorporeal blood circuits A61M1/3626
• CPC Class Codes: F04B 43/0081 systems, control, safety measures
• CPC Class Codes: F04B 51/00 Testing machines, pumps, or pumping installations
• CPC Class Codes: G01F 1/74 Devices for measuring flow of a fluid or flow of a fluent solid material in suspension in another fluid

Abstract

Various systems and methods for detecting air in a chamber of an infusion system are disclosed. In one embodiment, a determination is made that air is contained in the chamber on the basis of a change in the average force exerted against the plunger utilizing a derivative spike for event detection and a systematic reduction in the average force to confirm the nature of the change. In another embodiment, a determination is made that the chamber contains air when a difference between the current force profile and a baseline force profile crosses a threshold. In an additional embodiment, a force profile is classified as being an air force profile or a liquid force profile based on extracted features of the force profile.

Claims

1. A method for detecting air in a chamber of an infusion system comprising:

moving, with an actuator device, a plunger against a chamber containing fluid;

detecting, with a sensor, a force acting on the plunger as it moves against the chamber;

electronically communicating a measurement of the force from the sensor to a processor; and

determining, with the processor, that the chamber contains air when;

(1) a trigger event occurs in which a change in the force exceeds a threshold; and

(2) subsequent to the trigger event a differential between a baseline average force acting on the plunger and a current average force acting on the plunger exceeds an expected force differential within a defined delay range.

2. The method of claim 1 wherein (1) the trigger event further comprises a derivative force acting on the plunger per delivered volume of the fluid exiting the chamber exceeding a derivative threshold.

3. The method of claim 2 wherein (1) further comprises, for a consecutive number of measured points of a cycle of the plunger from the trigger event, the derivative force acting on the plunger per the delivered volume of the fluid exiting the chamber continuing to exceed the derivative threshold for more than a threshold number of the measured points of the cycle of the plunger against the chamber.

4. The method of claim 1 wherein the baseline average force comprises the average force acting on the plunger over a defined baseline range occurring up to the trigger event.

5. The method of claim 1 wherein the baseline average force represents the chamber being filled with the fluid.

6. A method for detecting air in a chamber of an infusion system comprising:

moving, with an actuator device, a plunger against a chamber containing fluid;

detecting, with a sensor, a force acting on the plunger as it moves against the chamber;

electronically communicating a measurement of the force from the sensor to a processor; and

determining with the processor;

(1) a baseline force profile;

(2) a current force profile representing the current force acting on the plunger against the chamber;

(3) a difference between the current force profile and the baseline force profile; and

(4) that the chamber contains air when the calculated difference crosses a threshold.

7. The method of claim 6 wherein the baseline force profile represents the chamber being filled with the fluid.

8. The method of claim 6 wherein the processor determines the baseline force profile by taking force measurements at a plurality of plunger positions over a cycle of the plunger against the chamber.

9. The method of claim 6 wherein the processor determines the baseline force profile by averaging force measurements taken over a plurality of cycles of the plunger against the chamber.

10. The method of claim 9 wherein the processor determines the baseline force by additionally taking into account the current force profile acting on the plunger during a current cycle of the plunger against the chamber.

11. The method of claim 10 wherein the processor further applies a forgetting rate which controls what percentage of the baseline force profile is made up of the average force measurements and what percentage of the baseline force profile is made up of the current force profile.

12. The method of claim 6 wherein the processor determines the current force profile by taking force measurements at a plurality of plunger positions over a current cycle of the plunger against the chamber.

13. The method of claim 6 wherein the processor calculates the difference between the current force profile and the baseline force profile by calculating respective differences between a plurality of points of the current force profile relative to a respective plurality of points of the baseline force profile, and determining a minimum difference of the respective differences.

14. The method of claim 13 wherein the processor determines that the chamber contains the air when the minimum difference is less than the threshold.

15. The method of claim 6 wherein the processor determines that the chamber contains the air when the calculated difference is below the threshold.

16. A method for detecting air in a chamber of an infusion system comprising:

moving, with an actuator device, a plunger against a chamber containing fluid;

detecting, with a sensor, a force acting on the plunger as it moves against the chamber;

electronically communicating a measurement of the force from the sensor to a processor; and

with the processor;

(1) preprocessing a force profile detected by the sensor;

(2) extracting features from the force profile; and

(3) classifying the force profile as being an air force profile or a liquid force profile based on the extracted features of the force profile.

17. The method of claim 16 wherein the processor classifies the force profile as being the air force profile or the liquid force profile without applying signal normalization to normalize to a baseline force profile.

18. The method of claim 16 wherein the processor preprocesses the force profile detected by the sensor by:

acquiring the force profile;

re-sampling the force profile for a set of angles;

selecting a sub-set of angles for the force profile; and

calculating a derivative of the force profile based on the force profile at the sub-set of angles.

19. The method of claim 16 wherein the processor preprocesses the force profile detected by the sensor by:

acquiring the force profile;

applying a low pass filter to the force profile;

re-sampling the force profile for a set of angles;

applying a range limit to the force profile; and

calculating a difference of the force profile.

20. The method of claim 16 wherein the processor extracts the features from the force profile by calculating scores of the force profile or applying a linear discriminate analysis to the force profile.