Malfunction detection with derivative calculation
Systems and methods of detecting occlusions and fluid-loss conditions (e.g., disconnects and/or leakages) in an infusion pump are discussed. For example, electrokinetic infusion pumps may develop an occlusion in the fluid flow path, which can disrupt control of fluid dispersed from the pump. As well, an infusion set disconnect can also result in a fluid-loss that can be disruptive. Such disruptions can be troublesome to systems that control the infusion pump, such as closed loop controllers. Accordingly, systems and methods described herein can be used to detect such occlusions and fluid-loss conditions during infusion pump operation. For example, a position sensor can be used to monitor fluid flow from the infusion pump, with the measurement being compared with an expected value to detect an occlusion or fluid-loss condition. Other algorithms for utilizing the position sensor are also described.
1. A method for detecting a malfunction in an infusion pump having a non-mechanically driven movable partition, comprising:
(a) for each of a plurality of instances:
(i) activating the infusion pump for a first pre-determined amount of time to induce movement of the movable partition of the pump and to release a shot of fluid from the pump,
(ii) de-activating the infusion pump for a second pre-determined amount of time, and
(ii) determining a position of the movable partition using a sensor;
(b) calculating a derivative for each of the plurality of instances, the derivative being based on a change in position of the movable partition with respect to a change in the number of shots released;
(c) calculating a moving average using calculated derivative values corresponding to each of the plurality of instances; and
(d) comparing the calculated moving average with a predetermined threshold value, to determine whether the infusion pump is malfunctioning.
2. The method of claim 1 , wherein the pre-determined threshold value is a minimum acceptable value for the calculated moving average.
3. The method of claim 2 , wherein comparing the calculated moving average to the pre-determined threshold value further comprises triggering a positive occlusion flag if the calculated moving average is less than the pre-determined threshold value.
4. The method of claim 3 , further comprising:
serially repeating steps (i), (ii), (iii), (b), (c), and (d) during operation of the infusion pump,
wherein the steps of comparing the calculated moving average include indicating the presence of an occlusion if the positive occlusion flag occurs at least a predetermined number of consecutive times.
5. The method of claim 4 , wherein indicating the presence of an occlusion includes generating an alarm signal.
6. The method of claim 1 , wherein the pre-determined threshold value is a maximum acceptable value for the calculated moving average.
7. The method of claim 6 , wherein comparing the calculated moving average to the pre-determined threshold value further comprises triggering a positive fluid-loss condition flag if the calculated moving average is greater than the pre-determined threshold value.
8. The method of claim 7 , further comprising:
serially repeating steps (i), (ii), (iii), (b), (c), and (d) during operation of the infusion pump,
wherein the steps of comparing the calculated moving average include indicating the presence of a fluid-loss condition if the positive fluid-loss condition flag occurs at least a predetermined number of consecutive times.
9. The method of claim 8 , wherein indicating the presence of a fluid-loss condition includes generating an alarm signal.
10. The method of claim 1 , wherein determining a position of the movable partition occurs before de-activating the infusion pump.
11. The method of claim 1 , wherein calculating the derivative includes using a last two known positions of the moveable partition for each of the plurality of instances.
12. The method of claim 1 , wherein the plurality of instances includes at least three instances.
13. The method of claim 1 , wherein determining the position of the movable partition further comprises using a magnetic sensor.
14. The method of claim 1 , wherein calculating the moving average includes multiplying the calculated derivative values by a weighting factor.
15. The method of claim 1 , wherein the infusion pump is an electrokinetic infusion pump.
16. A system for detecting a malfunction in an infusion pump, comprising:
an infusion pump having a non-mechanically driven movable partition disposed therein;
a position sensor disposed on the pump;
a controller associated with the infusion pump and adapted to operate the infusion pump in an activate/de-activate cycle, the cycle comprising activating the pump for a first pre-determined amount of time to induce movement of the movable partition and release a shot of fluid, and de-activating the pump for a second pre-determined amount of time; and
a processor associated with the position sensor, the processor adapted to determine whether the infusion pump is malfunctioning at least by comparing a calculated moving average of a plurality of derivatives to a pre-determined threshold value, each derivative based on a change in position of the movable partition with respect to a change in the number of shots released by the pump.
17. The system of claim 16 , wherein the position sensor comprises at least one of a magnetic sensor, an optical sensor, and a linear variable differential transformer.
18. The system of claim 16 , wherein the pre-determined threshold value is a minimum acceptable value for the calculated moving average.
19. The system of claim 18 , wherein the processor is configured to provide a positive occlusion flag if the calculated moving average is less than the pre-determined threshold value.
20. The system of claim 19 , wherein the processor is configured to produce an occlusion detection signal if the positive occlusion flag signal is produced after each of at least a predetermined number of consecutive cycles.
21. The system of claim 20 , wherein the predetermined number of cycles is at least three.
22. The system of claim 16 , wherein the processor is configured to calculate the moving average based upon calculated derivatives from at least a last three cycles.
23. The system of claim 16 , wherein the processor is configured to calculate the moving average based upon calculated derivatives from a last five cycles.
24. The system of claim 16 , wherein the pre-determined threshold value is a maximum acceptable value for the calculated moving average.
25. The system of claim 24 , wherein the processor is configured to provide a positive fluid-loss flag if the calculated moving average is greater than the pre-determined threshold value.
26. The system of claim 25 , wherein the processor is adapted to produce a fluid-loss detection signal if the positive fluid-loss flag signal is produced after each of at least a predetermined number of consecutive cycles.
27. The system of claim 16 , further comprising an alarm coupled to the processor for producing an alarm signal when the processor determines that the infusion pump is malfunctioning.
28. The system of claim 16 , wherein the infusion pump is an electrokinetic infusion pump.