Method for calibrating sensors used in diagnostic testing

• US 6,123,827 A
• Filed: 09/03/1998
• Issued: 09/26/2000
• Est. Priority Date: 01/17/1997
• Status: Expired due to Term

• Current Assignee: Segars California Partners, LP
• Original Assignee: VIA Medical Corporation (Medtronic Plc)
• Inventors: Rong, Daiting, Buse, David, Savage, Laurel, Wong, David K.
• Primary Examiner(s): TUNG, TA HSUNG
• Application Number:
  US09/146,986
• Time in Patent Office: 754 Days
• Field of Search: 204/415, 204/433, 205/787.5, 205/783, 205/775, 436/9, 436/11
• US Class Current: 205/775
• CPC Class Codes: A61B 5/14539 for measuring pH
• CPC Class Codes: A61B 5/14542 for measuring blood gases A61B5/14551 takes precedence
• CPC Class Codes: A61B 5/14546 for measuring analytes not otherwise provided for, e.g. ions, cytochromes
• CPC Class Codes: A61B 5/1468 using chemical or electrochemical methods, e.g. by polarographic means A61B5/1486 takes precedence
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: G01N 33/4925 measuring blood gas content, e.g. O2, CO2 , HCO3
• CPC Class Codes: Y10T 436/100833 Simulative of a gaseous composition
• CPC Class Codes: Y10T 436/102499 Blood gas standard or control

Abstract

A method is disclosed for reliably calibrating a sensor used in diagnostic sensing of a predetermined parameter, e.g., CO₂ partial pressure, O₂ partial pressure, or pH, of a solution such as blood, the method compensating for expected variations over time in the value of the parameter in a calibration solution. The parameter of the calibration solution has a predetermined initial value, and the solution is initially located within a container that is configured to allow the value of that parameter to vary over time in a predetermined manner. Supplying the calibration solution to the sensor causes the sensor to produce a calibration solution signal, which is compared with a calculated value for the parameter based on its expected variation over time, to produce a calibration factor. Thereafter supplying the test fluid to the sensor causes the sensor produces a test fluid signal, and this test fluid signal then is adjusted in accordance with the calibration factor.

Claims

1. A method for calibrating a sensor of a kind that measures a predetermined parameter of a test fluid, comprising:

placing a calibration solution in a container, wherein a predetermined parameter of the calibration solution has a predetermined value, and wherein the container is configured such that the value of the predetermined parameter can vary over time in a predetermined manner;

exposing the sensor to calibration solution supplied from the container, whereupon the sensor produces a calibration solution signal;

calculating the value of the predetermined parameter of the calibration solution supplied to the sensor based on its expected variation over time, and comparing the calculated value with the calibration solution signal actually produced by the sensor, to produce a calibration factor;

exposing the sensor to the test fluid, whereupon the sensor produces a test fluid signal; and

adjusting the test fluid signal in accordance with the calibration factor, to produce a calibrated test fluid signal.

2. A method as defined in claim 1, wherein:

the predetermined parameter of the test fluid to be measured is CO₂ partial pressure;

the sensor is configured to measure CO₂ partial pressure;

the calibration solution has a predetermined initial concentration of CO₂ ;

the container has a porosity that allows CO₂ to escape from the calibration solution over time in a predetermined manner; and

calculating includes calculating the concentration of CO₂ in the calibration solution supplied to the CO₂ sensor based on its expected escape from the container over time.

3. A method as defined in claim 2, wherein:

the container for the calibration solution includes a flexible bag and an intravenous line;

the flexible bag allows CO₂ to escape over time from the calibration solution it carries in a first predetermined manner, and the intravenous line allows CO₂ to escape over time from the calibration solution it carries in a second predetermined manner; and

calculating includes calculating the concentration of CO₂ in the calibration solution supplied to the CO₂ sensor based on its expected escape over time from both the flexible bag and the intravenous line.

4. A method as defined in claim 3, wherein calculating includes determining the time durations the calibration solution supplied to the CO₂ sensor has dwelled in both the flexible bag and the intravenous line.

5. A method as defined in claim 2, wherein calculating includes measuring the temperature of the calibration solution in the container and determining the expected escape of CO₂ over time based on the measured temperature.

6. A method as defined in claim 2, and further including:

exposing a second, pH-responsive sensor to the calibration solution, whereupon the second, pH-responsive sensor produces a calibration solution pH signal;

calculating the pH of the calibration solution supplied to the second, pH-responsive sensor based on the expected escape of CO₂ from the container over time, and comparing the calculated pH with the calibration solution pH signal actually produced by the second, pH-responsive sensor, to produce a pH calibration factor;

exposing the second, pH-responsive sensor to the test fluid, hereupon the second, pH-responsive sensor produces a test fluid pH signal; and

adjusting the test fluid pH signal in accordance with the pH calibration factor.

7. A method as defined in claim 1, wherein:

the calibration solution is infusible into a patient;

the test fluid is blood;

the method is implemented as part of an infusion fluid delivery apparatus that includes a sensor assembly that houses the CO₂ sensor;

exposing the sensor to calibration solution includes pumping the calibration solution through the sensor assembly and into the patient; and

exposing the sensor to the test fluid includes drawing blood from the patient into the sensor assembly.

8. A method as defined in claim 1, wherein:

the sensor is configured to measure pH;

the calibration solution has a predetermined initial concentration of CO₂ ;

the container has a porosity that allows the CO₂ to escape from the calibration solution over time in a predetermined manner; and

calculating includes calculating the concentration of CO₂ in the calibration solution supplied to the pH sensor based on its expected escape from the container over time, and calculating the pH of the calibration solution supplied to the pH sensor based on the calculated concentration of CO₂.

9. A method as defined in claim 8, wherein:

the container for the calibration solution includes a flexible bag and an intravenous line;

the flexible bag allows CO₂ to escape over time from the calibration solution it carries in a first predetermined manner, and the intravenous line allows CO₂ to escape over time from the calibration solution it carries in a second predetermined manner; and

calculating includes calculating the pH of the calibration solution supplied to the pH sensor based on the expected escape of CO₂ over time from both the flexible bag and the intravenous line.

10. A method as defined in claim 9, wherein calculating includes determining the time durations the calibration solution supplied to the pH sensor has dwelled in both the flexible bag and the intravenous line.

11. A method as defined in claim 9, wherein calculating includes measuring the temperature of the calibration solution in the container and determining the expected escape of CO₂ over time based on the measured temperature.

12. A method as defined in claim 1, wherein:

the predetermined parameter of the test fluid to be measured is O₂ partial pressure;

the sensor is configured to measure O₂ partial pressure;

the calibration solution has a predetermined initial O₂ partial pressure;

the method further includes measuring the temperature of the calibration solution carried by the container;

the container has a porosity that allows the O₂ partial pressure of the calibration solution it carries to vary over time according to variations in the temperature of the calibration solution; and

calculating includes calculating the O₂ partial pressure of the calibration solution supplied to the O₂ sensor based on the measured temperature of the calibration solution.

13. A method as defined in claim 12, wherein:

the container for the calibration solution includes a flexible bag and an intravenous line;

the flexible bag has a porosity that allows O₂ to pass through it over time in a first predetermined manner, and the intravenous line likewise has a porosity that allows O₂ to pass through it over time in a second predetermined manner; and

calculating includes calculating the concentration of O₂ in the calibration solution supplied to the O₂ sensor based on its expected passage over time through both the flexible bag and the intravenous line.

14. A method as defined in claim 13, wherein calculating includes determining the time durations the calibration solution supplied to the O₂ sensor has dwelled in both the flexible bag and the intravenous line.

15. A method as defined in claim 12, wherein calculating includes measuring the temperature of the calibration solution in the container and determining the expected passage of O₂ over time through both the flexible bag and the intravenous line, based on the measured temperature.

16. A method as defined in claim 12, and further comprising:

measuring the pressure of the ambient environment; and

adjusting the calculated value of O₂ partial pressure of the calibration solution based on the measured pressure of the ambient environment.

17. A method as defined in claim 1, wherein:

the predetermined parameter of the test fluid to be measured is the partial pressure of a predetermined gas;

the partial pressure of the predetermined gas in the calibration solution has a predetermined initial value;

the sensor is configured to measure the partial pressure of the predetermined gas;

the container has a porosity that allows the partial pressure of the calibration solution it carries to vary over time in a predetermined manner; and

calculating includes calculating the partial pressure of the predetermined gas in the calibration solution supplied to the sensor based on its known variation over time.

18. A method for calibrating a sensor of a kind that measures a predetermined parameter of a patient'"'"'s blood, comprising:

providing an infusion apparatus that includes an infusion fluid bag, an intravenous line, a sensor assembly that incorporates the sensor, and a pump;

placing a calibration solution in the infusion fluid bag, wherein a predetermined parameter of the calibration solution has a predetermined initial value, and wherein the value of the predetermined parameter of the calibration solution carried by the infusion fluid bag and the intravenous line can vary over time in a predetermined manner;

pumping the calibration solution from the infusion fluid bag through the intravenous line and the sensor assembly to the patient, whereupon the sensor produces a calibration solution signal;

calculating the value of the predetermined parameter of the calibration solution pumped through the sensor assembly based on its expected variation over time, and comparing the calculated concentration with the calibration solution signal actually produced by the sensor, to produce a calibration factor;

drawing blood from the patient into the sensor assembly, whereupon the sensor produces a blood signal; and

adjusting the blood signal in accordance with the calibration factor.

19. A method as defined in claim 18, wherein:

the predetermined parameter of the blood to be measured is CO₂ partial pressure;

the sensor is configured to measure CO₂ partial pressure;

the calibration solution has a predetermined initial concentration of CO₂ ;

the infusion fluid bag has a porosity that allows CO₂ to escape from the calibration solution over time in a predetermined manner; and

calculating includes calculating the concentration of CO₂ in the calibration solution supplied to the CO₂ sensor based on its expected escape from the infusion fluid bag over time.

20. A method as defined in claim 19, wherein:

the infusion fluid bag allows CO₂ to escape over time from the calibration solution it carries in a first predetermined manner, and the intravenous line allows CO₂ to escape over time from the calibration solution it carries in a second predetermined manner; and

calculating includes calculating the concentration of CO₂ in the calibration solution supplied to the CO₂ sensor based on its expected escape over time from both the infusion fluid bag and the intravenous line.

21. A method as defined in claim 20, wherein calculating includes determining the time durations the calibration solution supplied to the CO₂ sensor has dwelled in both the flexible bag and the intravenous line.

22. A method as defined in claim 19, wherein calculating includes measuring the temperature of the calibration solution in the container and determining the expected escape of CO₂ over time based on the measured temperature.

23. A method as defined in claim 19, and further including:

exposing a second, pH-responsive sensor to the calibration solution, whereupon the second, pH-responsive sensor produces a calibration solution pH signal;

calculating the pH of the calibration solution supplied to the second pH-responsive sensor based on the expected escape of CO₂ from the infusion fluid bag over time, and comparing the calculated pH with the calibration solution pH signal actually produced by the second, ph-responsive sensor, to produce a pH calibration factor;

exposing the second, pH-responsive sensor to the blood, whereupon the sensor produces a blood pH signal; and

adjusting the blood pH signal in accordance with the pH calibration factor.

24. A method as defined in claim 18, wherein:

the sensor is configured to measure pH;

the calibration solution has a predetermined initial concentration of CO₂ ;

the infusion fluid bag has a porosity that allows the CO₂ to escape from the calibration solution over time in a predetermined manner; and

calculating includes calculating the concentration of CO₂ in the calibration solution supplied to the pH sensor based on its expected escape from the infusion fluid bag over time, and calculating the pH of the calibration solution supplied to the pH sensor based on the calculated concentration of CO₂.

25. A method as defined in claim 24, wherein:

the infusion fluid bag allows CO₂ to escape over time from the calibration solution it carries in a first predetermined manner, and the intravenous line allows CO₂ to escape over time from the calibration solution it carries in a second predetermined manner; and

calculating includes calculating the pH of the calibration solution supplied to the pH sensor based on the expected escape of CO₂ over time from both the infusion fluid bag and the intravenous line.

26. A method as defined in claim 24, wherein calculating include determining the time durations the calibration solution supplied to the pH sensor has dwelled in both the infusion fluid bag and the intravenous line.

27. A method as defined in claim 24, wherein calculating includes measuring the temperature of the calibration solution in the infusion fluid bag and determining the expected escape of CO₂ over time based on the measured temperature.

28. A method as defined in claim 18, wherein:

the predetermined parameter of the blood to be measured is O₂ partial pressure;

the sensor is configured to measure O₂ partial pressure;

the calibration solution has a predetermined initial O₂ partial pressure;

the method further includes measuring the temperature of the calibration solution carried by the infusion fluid bag;

the infusion fluid bag has a porosity that allows the O₂ partial pressure of the calibration solution it carries to vary over time according to variations in the temperature of the calibration solution; and

calculating includes calculating the O₂ partial pressure of the calibration solution supplied to the O₂ sensor based on the measured temperature of the calibration solution.

29. A method as defined in claim 28, wherein:

the infusion fluid bag has a porosity that allows O₂ to pass through it over time in a first predetermined manner, and the intravenous line likewise has a porosity that allows O₂ to pass through it over time in a second predetermined manner; and

calculating includes calculating the concentration of O₂ in the calibration solution supplied to the O₂ sensor based on its expected passage over time through both the infusion fluid bag and the intravenous line.

30. A method as defined in claim 29, wherein calculating includes determining the time durations the calibration solution supplied to the O₂ sensor has dwelled in both the infusion fluid bag and the intravenous line.

31. A method as defined in claim 28, wherein calculating includes measuring the temperature of the calibration solution in the infusion fluid bag and determining the expected passage of O₂ over time through both the infusion fluid bag and the intravenous line, based on the measured temperature.

32. A method as defined in claim 28, and further comprising:

measuring the pressure of the ambient environment; and

adjusting the calculated value of O₂ partial pressure of the calibration solution based on the measured pressure of the ambient environment.

33. A method as defined in claim 18, wherein:

the predetermined parameter of the blood to be measured is the partial pressure of a predetermined gas;

the partial pressure of the predetermined gas in the calibration solution has a predetermined initial value;

the sensor is configured to measure the partial pressure of the predetermined gas;

the infusion fluid bag has a porosity that allows the partial pressure of the calibration solution it carries to vary over time in a predetermined manner; and

calculating includes calculating the partial pressure of the predetermined gas in the calibration solution supplied to the sensor based on its known variation over time.