Occlusion detection system

• US 8,378,837 B2
• Filed: 02/18/2010
• Issued: 02/19/2013
• Est. Priority Date: 02/20/2009
• Status: Active Grant

• Current Assignee: ICU Medical Incorporated
• Original Assignee: Hospira Incorporated (Pfizer Inc.)
• Inventors: Wang, YiFei, Liu, Chang, Ng, See Hai
• Primary Examiner(s): Phan, Hai
• Assistant Examiner(s): Knox, Kaleria
• Application Number:
  US12/707,774
• Publication Number:
  US 20100214110A1
• Time in Patent Office: 1,097 Days
• Field of Search: 604/151, 604/67, 604/122, 340/665, 340/511
• US Class Current: 340/665
• CPC Class Codes: A61M 2005/16863 Occlusion detection
• CPC Class Codes: A61M 2205/18 with alarm
• CPC Class Codes: A61M 2205/332 Force measuring means
• CPC Class Codes: A61M 5/1456 with a replaceable reservoir comprising a piston rod to be moved into the reservoir, e.g. the piston rod is part of the removable reservoir
• CPC Class Codes: A61M 5/16854 by monitoring line pressure

Abstract

A method of monitoring pressure inside a fluid line and a system for implementing the method. The method is applicable to syringe pump systems. The method includes the steps of measuring a force value caused by a pressure inside the fluid line; collecting the measured force values during at least two consecutive moving time windows; calculating a slope of a best-fit line within each time window; calculating a slope difference of the slopes of the best-fit lines; comparing the slope difference with a pre-determined threshold gradient value; defining a baseline force as the detected force value when the slope difference is equal to the threshold gradient value; determining a relative force value by subtracting the baseline force from the detected force value; and, triggering an alarm if the relative force is greater than a pre-defined threshold force.

Claims

1. A method of monitoring pressure inside a fluid line, comprising the steps of:

measuring a force value caused by a pressure inside the fluid line;

collecting and storing force values during at least two consecutive time windows;

calculating a slope of a best-fit line based upon the force values within each time window;

calculating a slope difference between the slopes of the best-fit lines;

comparing the slope difference with a pre-determined threshold gradient value;

defining a baseline force as the measured force value when the slope difference is at least equal to the threshold gradient value;

calculating a relative force value by subtracting the baseline force from the measured force value; and

,

initiating an alarm if the relative force value is greater than a value of the pre-defined threshold force value.

2. The method of claim 1 wherein the best-fit line is obtained by a linear regression equation.

3. The method of claim 1 wherein the threshold gradient value is defined as the slope difference equal to 50% of a maximum slope difference at a selected flow rate.

4. The method of claim 1 wherein the threshold gradient value is determined based on a size of a syringe connected to the fluid line.

5. The method of claim 4 wherein for a 60 cc syringe, the threshold gradient value is equal to 80% of a maximum slope difference at a selected flow rate.

6. The method of claim 4 wherein for a 30 cc syringe, the threshold gradient value is equal to 100% of a maximum slope difference at a selected flow rate.

7. The method of claim 4 wherein for a 20 cc syringe, the threshold gradient value is equal to 107% of a maximum slope difference at a selected flow rate.

8. The method of claim 4 wherein for a 10 cc syringe, the threshold gradient value is equal to 89% of a maximum slope difference at a selected flow rate.

9. The method of claim 4 wherein for a 5 cc syringe, the threshold gradient value is equal to 80% of a maximum slope difference at a selected flow rate.

10. The method of claim 4 wherein for a 3 cc syringe, the threshold gradient value is equal to 49% of a maximum slope difference at a selected flow rate.

11. The method of claim 4 wherein for a 1 cc syringe, the threshold gradient value is equal to 18% of a maximum slope difference at a selected flow rate.

12. The method of claim 1 wherein a window size for a flow rate is selected based on a best-fit line for an average between an optimal and a minimum window size for a range of flow rates.

13. A method of monitoring pressure inside a fluid line, comprising the steps of:

measuring a force value caused by a pressure inside the fluid line;

collecting and storing force values during at least two consecutive time windows;

calculating a slope of a best-fit line based upon the force values within each time window, wherein the best-fit line is obtained by a linear regression equation;

calculating a slope difference between the slopes of the best-fit lines;

comparing the slope difference with a pre-determined threshold gradient value;

defining a baseline force value as the measured force value when the slope difference is at least equal to the threshold gradient value;

calculating a baseline pressure value corresponding to the baseline force value;

calculating a current pressure value from the measured force value;

calculating a relative pressure value by subtracting the baseline pressure value from the current pressure value;

comparing the relative pressure value to a pre-determined pressure threshold value;

and initiating an alarm if the current pressure value is greater than the pre-determined pressure threshold value.

14. The method of claim 13, wherein the alarm includes a control signal.

15. An occlusion detection system comprising:

a pump having a sensor operatively connected to a fluid line for delivering fluid for the pump, and a processor, wherein the processor;

uses at least two consecutive moving time windows to process measured force values detected by the sensor;

calculates a slope of a best-fit line for the measured force values collected within each time window,

calculates a slope difference of the slopes of the best-fit lines;

selects a threshold gradient value based on the size of the syringe;

compares the slope difference to the threshold gradient value;

defines a baseline force value as the measured force value when the slope difference is equal to the threshold gradient value;

compares the measured force value with the baseline force value to calculate a relative force value; and

,

initiates an alarm if the relative force value exceeds a pre-determined threshold force value.

16. The system of claim 15 wherein the threshold force value is determined based on an internal diameter of a portion of the fluid line defined by a syringe.

17. The system of claim 15 wherein the sensor is a loadcell sensor.

18. The system of claim 15, wherein a current pressure value is calculated corresponding to the measured force value;

the current pressure value is compared to a pre-determined pressure threshold value; and

an alarm is initiated if the current pressure value exceeds the pre-determined threshold value.