METHODS OF CALIBRATING A SENSOR IN A PATIENT MONITORING SYSTEM

• US 20110120206A1
• Filed: 02/19/2009
• Published: 05/26/2011
• Est. Priority Date: 02/19/2008
• Status: Active Grant

• Current Assignee: Sphere Medical Limited (Sphere Medical Holding Ltd.)
• Original Assignee: Sphere Medical Limited (Sphere Medical Holding Ltd.)
• Inventors: Laitenberger, Peter, Troughton, Gavin
• Granted Patent: US 8,869,585 B2
• Time in Patent Office: Days
• US Class Current: 73/1.06
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes

Abstract

The present application discloses a number of methods of calibrating a sensor for measuring an analyte in a patient monitoring system. In a first embodiment, the method comprises calculating a sensor drift; calibrating the sensor using at least one calibration fluid; and periodically updating the sensor calibration based on the sensor drift calculation. In a second embodiment, the system comprises means for adjusting a gas concentration in a fluid, and the method comprises providing a calibration fluid; setting the analyte concentration in the first fluid to a first concentration with said adjusting means; measuring the first analyte concentration with the sensor; setting the analyte concentration in the first fluid to a second concentration with said adjusting means; measuring the second analyte concentration with the sensor; and determining the calibration coefficients for the sensor from the measured first analyte concentration and the measured second analyte concentration. In a third embodiment, the method comprises exposing the sensor to a first fluid comprising a first unknown concentration of the analyte; measuring the first unknown analyte concentration with the sensor; determining the first unknown analyte concentration with an analyser external to the patient monitoring system; providing the sensor with the determined first analyte concentration, and determining the calibration coefficients for the sensor from the measured first unknown analyte concentration and the analyte concentration determined by the analyser. At least some of the above embodiments ensure that the period between recalibrations of the sensor is extended, thus reducing the number of disruptions to the sensor monitoring process.

Claims

1. A method of calibrating a sensor for measuring an analyte in a patient monitoring system, the method comprising:

calculating a sensor drift;

calibrating the sensor using at least one calibration fluid; and

periodically updating the sensor calibration based on the sensor drift calculation.

2. A method as claimed in claim 1, further comprising:

providing the sensor with a first fluid comprising a predetermined concentration of an analyte;

performing a first measurement of the analyte concentration in the first fluid with the sensor;

providing the sensor with a further fluid comprising a further predetermined concentration of an analyte; and

performing at least one additional measurement of the further analyte concentration in the further fluid with the sensor after a predetermined time period;

and wherein the step of calculating the sensor drift comprises calculating said drift from the difference between the first measured analyte concentration and the further measured analyte concentration.

3. A method as claimed in claim 2, wherein the first fluid and the further fluid are the same fluid.

4. A method as claimed in claim 2 or 3, wherein the patient monitoring system comprises means for adjusting a gas concentration in the system, and wherein the analyte is said gas, the method further comprising:

maintaining a well-defined concentration of the gas in the first fluid with said means for adjusting a gas concentration during the first measurement and the further measurement.

5. A method as claimed in claim 4, wherein the gas comprises at least one of oxygen and carbon dioxide.

6. A method as claimed in claim 3, wherein the sensor is arranged to determine the analyte concentration in a flowing sample, the method further comprising the step of maintaining the first fluid stationary over the sensor during a time period including the first measurement and the further measurement.

7. A method as claimed in any of claims 2-6, wherein the sensor comprises a means for altering the analyte concentration, and wherein the step of calculating the drift comprises determining said drift based on a difference between the first measurement and the second measurement and a deviation of said difference from a predicted difference based on the known analyte consumption rate of said altering means.

8. A method as claimed in any of claims 2-7, wherein one of the first fluid and the further fluid comprises the patient'"'"'s blood.

9. A method as claimed in claim 3, further comprising the step of stabilising the sensor with a priming fluid, said priming fluid comprising a first predetermined concentration of the analyte, and wherein:

the first fluid comprises the priming fluid; and

the first analyte concentration and the further analyte concentration are determined during said stabilising.

10. A method as claimed in claim 12, or 3 wherein the step of calculating a sensor drift is performed during manufacturing of the sensor.

11. A method as claimed in claim 10, further comprising adjusting the calculated sensor drift based on said sensor calibration.

12. A method of calibrating a sensor for measuring an analyte in a patient monitoring system including means for adjusting the analyte concentration, the method comprising:

providing a calibration fluid;

setting the analyte concentration in the first fluid to a first concentration with said adjusting means;

measuring the first analyte concentration with the sensor;

setting the analyte concentration in the first fluid to a second concentration with said adjusting means;

measuring the second analyte concentration with the sensor; and

determining the calibration coefficients for the sensor from the measured first analyte concentration and the measured second analyte concentration.

13. A method as claimed in claim 12, further comprising the steps of:

periodically setting the analyte concentration in the first fluid to a further concentration with said adjusting means;

measuring the further analyte concentration with the sensor; and

adjusting the calibration coefficients for the sensor based on the measured further analyte concentration.

14. A method as claimed in claim 12 or 13, wherein said analyte is a gas.

15. A method as claimed in claim 14, wherein the gas comprises at least one of oxygen and carbon dioxide, and said adjusting means comprise an oxygenator.

16. A method as claimed in claim 14, wherein the system comprises a shunt line, said sensor being located in the shunt line, and wherein the shunt line is coupled to said adjusting means.

17. A method of calibrating a sensor for measuring an analyte in a patient monitoring system, the method comprising:

exposing the sensor to a first fluid comprising a first unknown concentration of the analyte;

measuring the first unknown analyte concentration with the sensor;

determining the first unknown analyte concentration with an analyser external to the patient monitoring system;

providing the sensor with the determined first analyte concentration, and

determining the calibration coefficients for the sensor from the measured first unknown analyte concentration and the analyte concentration determined by the analyser.

18. A method as claimed in claim 17, further comprising the steps of:

exposing the sensor to a second fluid comprising a further analyte concentration;

measuring the further analyte concentration with the sensor; and

wherein said determining step comprises determining the calibration coefficients for the sensor from the measured first unknown analyte concentration, the analyte concentration determined by the analyser and the measured further analyte concentration.

19. A method as claimed in claim 18, wherein the further analyte concentration is a further unknown analyte concentration, and wherein the method further comprises:

determining the further unknown analyte concentration with the analyser; and

providing the sensor with the determined further analyte concentration, and wherein said calibration coefficients determining step comprises determining the calibration coefficients for the sensor from the measured first unknown analyte concentration, the measured further unknown analyte concentration and the respective analyte concentrations determined by the analyser.

20. A method as claimed in any of claims 17-19, wherein one of the first fluid and the second fluid is a priming solution.

21. A method as claimed in any of claim 17-20, wherein one of the first fluid and the second fluid comprises blood.

22. A method as claimed in any of claims 18-21, wherein the sensor is exposed to the second fluid before being exposed to the first fluid.