Extravasation detector using microwave radiometry

• US 6,375,624 B1
• Filed: 09/17/1999
• Issued: 04/23/2002
• Est. Priority Date: 06/14/1996
• Status: Expired due to Fees

• Current Assignee: Medrad Incorporated (Bayer AG)
• Original Assignee: Medrad Incorporated (Bayer AG)
• Inventors: Uber, Arthur E. III, Griffiths, David M.
• Primary Examiner(s): Jaworski, Francis J.
• Application Number:
  US09/398,658
• Time in Patent Office: 949 Days
• Field of Search: 600/549, 733/46, 604/49-50, 604/52, 374/122, 374/148, 128/DIG.12, 128/13
• US Class Current: 600/549
• CPC Class Codes: A61M 5/16836 by sensing tissue properties at the infusion site, e.g. for detecting infiltration detecting tissue temperature for diagnostic purposes A61M39/0247
• CPC Class Codes: Y10S 128/13 Infusion monitoring

Abstract

A microwave antenna senses the temperature of tissue into which a fluid is to be injected. The fluid is injected by a needle or other vascular entry device connected to a fluid injector by a connector tube. The fluid temperature is measured by a temperature sensor attached to the connector tube. An alarm processor determines whether an extravasation occurs by comparing a temperature discrimination function derived from tissue temperature taken at different times with a calculated threshold value. The threshold value is calculated from the tissue temperature and the fluid temperature. The threshold value is recalculated and updated continuously during the fluid injection.

Claims

1. An apparatus for detecting extravasations in tissue injected with fluid, the apparatus comprising:

a fluid temperature sensor for sensing the temperature of fluid present in a fluid path element which transmits fluid to a patient and generating a fluid temperature signal in response thereto;

a tissue temperature sensor for sensing the temperature of tissue proximate to the site of injection and generating a tissue temperature signal in response thereto; and

a processor adaptable to periodically receive said tissue temperature signal and said fluid temperature signal, said processor having an alarm circuit for declaring the occurrence of an extravasation and a threshold calculation circuit for periodically calculating at least one threshold value as a function of said tissue temperature signal and said fluid temperature signal, said processor activating said alarm circuit as a function of said tissue temperature signal, said fluid temperature signal and said at least one threshold value during a fluid injection.

2. The apparatus of claim 1 wherein said fluid temperature sensor is associated with a connector tube.

3. The apparatus of claim 1 wherein said fluid temperature sensor is associated with a syringe.

4. The apparatus of claim 1 wherein said fluid temperature sensor is associated with a catheter.

5. The apparatus of claim 1 wherein said fluid temperature sensor comprises a microwave antenna and a radiometer coupled to the microwave antenna.

6. The apparatus of claim 1 wherein said tissue temperature sensor comprises a microwave antenna and a radiometer coupled to the microwave antenna.

7. The apparatus of claim 1 wherein said processor further comprises:

a circuit for deriving at least first and second tissue temperatures from said tissue temperature signal at different times;

a circuit for deriving a fluid temperature from said fluid temperature signal;

a memory for storing said first and second tissue temperatures and said fluid temperature;

a temperature discrimination function circuit for calculating a temperature discrimination function as a function of said first and second tissue temperatures; and

a comparison circuit for comparing said temperature discrimination function with said at least one threshold, said comparison circuit activating said alarm circuit to declare an extravasation when the value of said temperature discrimination function exceeds said at least one threshold.

8. The apparatus of claim 7 wherein said threshold calculation circuit calculates a first, positive threshold as a function of said second tissue temperature and said fluid temperature, said threshold calculation circuit further calculating a second negative threshold as a function of said second tissue temperature and said fluid temperature, said comparison circuit activating said alarm circuit when either the value of said temperature discrimination function exceeds said first threshold or when the value of said temperature discrimination function is less than said second negative threshold.

9. The apparatus of claim 7 wherein said temperature discrimination function circuit periodically calculates the temperature discrimination function as the difference between said fluid tissue temperature and each of a plurality of sequentially-determined second tissue temperatures.

10. The apparatus of claim 7 wherein said first tissue temperature is a tissue temperature at the beginning of the fluid injection and said second tissue temperature is a current tissue temperature.

11. The apparatus of claim 1 further comprising means for entering and storing at least one patient parameter said threshold calculation circuit calculating said at least one threshold value as a function of said at least one patient parameter.

12. The apparatus of claim 11 wherein said at least one patient parameter is selected from the group consisting of age, vein condition, vein size, vein depth, health of the patient, obesity, type of vascular entry device being employed, vascular insertion difficulty and needle positioning confidence.

13. The apparatus of claim 11, further comprising means for receiving a fluid flow rate for the fluid to be injected said threshold calculation circuit calculating said at least one threshold value as a function of said fluid flow rate.

14. The apparatus of claim 1 wherein said threshold circuit is further operable to take initial tissue and fluid temperatures and calculate a threshold value based on said initial tissue and fluid temperatures, and further wherein said processor further comprises a discrimination circuit operable to calculate a temperature discrimination function based on said initial tissue temperature and a current tissue temperature said discrimination circuit operable to activate said alarm circuit if said temperature discrimination function exceeds said initial threshold value.

15. The apparatus of claim 14 wherein said threshold circuit further comprises a circuit for determining updated fluid and tissue temperatures and a circuit for calculating an updated threshold value and further wherein said discrimination circuit further comprises a circuit for calculating an updated temperature discrimination function and a circuit for activating said alarm circuit if said updated temperature discrimination function exceeds said updated threshold value.

16. The apparatus of claim 1 wherein said processor further comprises a warning circuit which compares the difference of said fluid temperature and said tissue temperature to a minimal difference threshold to warn that no extravasation detection is possible.

17. An apparatus for detecting extravasations in tissue injected with fluid, the apparatus comprising:

a fluid temperature sensor for sensing the temperature of fluid proximate to the site of injection and generating a fluid temperature signal in response thereto;

a tissue temperature sensor for sensing the temperature of tissue proximate to the site of injection and generating a tissue temperature signal in response thereto; and

a processor adaptable to periodically receive said tissue temperature signal and said fluid temperature signal said processor having an alarm circuit for declaring the occurrence of an extravasation and a threshold calculation circuit for periodically calculating at least one threshold value as a function of said tissue temperature signal and said fluid temperature signal said processor activating said alarm circuit as a function of said tissue temperature signal said fluid temperature signal, and said at least one threshold value during a fluid injection.

18. A fluid temperature sensor comprising:

a temperature transducer operably associated with an extravasation detector; and

a thermally conductive insert coupled to said temperature transducer and operably associated with a fluid path element for delivering fluid to a patient during a fluid injection said insert adapted to extend through the fluid path element into contact with the fluid therein to provide a temperature conductive path between the fluid and said temperature transducer.

19. The fluid temperature sensor of claim 18 wherein said transducer comprises a thermistor.

20. The fluid temperature sensor of claim 18 wherein said transducer comprises a thermocouple.

21. A method of detecting extravasations in tissue injected with a fluid, comprising:

periodically sensing the temperature of the fluid present in a fluid path element transmitting fluid to a patient;

generating a fluid temperature signal in response to the periodic sensing of fluid temperature;

periodically sensing the temperature of tissue proximate to the site of injection;

generating a tissue temperature signal in response to the periodic sensing of tissue temperature;

receiving the fluid temperature signal and the tissue temperature signal;

storing a fluid temperature and a tissue temperature derived from the received signals; and

declaring the occurrence of an extravasation as a function of said tissue temperature signal and said fluid temperature signal during a fluid injection.

22. The method of claim 21 further comprising:

determining initial tissue and fluid temperatures;

calculating at least one initial threshold value as a function of the initial tissue and fluid temperatures;

calculating a temperature discrimination function based on the initial tissue temperature; and

activating an alarm if the temperature discrimination function exceeds the at least one initial threshold value.

23. The method of claim 22 further comprising:

determining updated fluid and tissue temperatures;

calculating at least one updated threshold value as a function of the updated fluid and tissue temperatures;

calculating an updated temperature discrimination function; and

activating the alarm if the updated temperature discrimination function exceeds the at least one updated threshold value.

24. The method of claim 22, further comprising:

comparing the difference between the fluid temperature and the tissue temperature to a minimal difference threshold; and

warning that no extravasation detection is possible if the minimal difference threshold exceeds the difference.

25. A method of detecting extravasations in tissue injected with a fluid, the method comprising:

measuring a tissue temperature;

measuring a fluid temperature;

controlling the fluid temperature so the difference between the tissue temperature and the fluid temperature is sufficient to permit extravasation detection; and

declaring the occurrence of an extravasation as a function of the tissue temperature and the fluid temperature.

26. A fluid injection system comprising:

an injector operable to initiate and terminate fluid flow into a patient;

a fluid path element coupled to said fluid injector for transmitting fluid to the patient;

a fluid temperature sensor associated with said fluid path element said temperature sensor producing a fluid temperature signal representing the temperature of the fluid in said fluid path element;

a tissue temperature sensor for generating a tissue temperature signal as a function of the temperature of the tissue of the patient proximate to the injection site; and

an alarm circuit coupled to said tissue temperature sensor and said fluid temperature sensor, said alarm circuit comprising a temperature discrimination function circuit operable to calculate a temperature discrimination function from the tissue temperature and a threshold circuit operable to compare at least a first threshold value with the temperature discrimination function, the threshold circuit calculating the at least a first threshold value at different time intervals during a fluid injection.

27. The fluid injection system of claim 26 wherein said tissue temperature sensor comprises an antenna disposed to receive microwave radiation from the tissue and a radiometer coupled to the antenna and operable to produce the tissue temperature signal.

28. The fluid injection system of claim 26 wherein said fluid temperature sensor comprises an antenna disposed to receive microwave radiation from the fluid and a radiometer coupled to the antenna for generating the fluid temperature signal.

29. The fluid injection system of claim 26 wherein said fluid path element comprises a syringe.

30. The fluid injection system of claim 26 wherein said fluid path element comprises a connector tube.

31. The fluid injection system of claim 26 wherein said fluid path element comprises a catheter.

32. The fluid injection system of claim 26 further comprising means for entering and storing at least one patient parameter and wherein the at least a first threshold value is calculated as a function of the at least one patient parameter.

33. The fluid injection system of claim 32 wherein the at least one patient parameter is selected from the group consisting of age, vein condition, vein size, vein depth, health of the patient, obesity, type of vascular entry device being employed, vascular insertion difficulty and needle positioning confidence.

34. An apparatus for detecting extravasations in tissue injected with a fluid, the apparatus comprising:

a tissue temperature sensor for sensing the temperature of the tissue proximate to the injection site and generating a tissue temperature signal in response thereto;

a fluid temperature controller for controlling the temperature of the fluid injected into the tissue; and

a processor adaptable to receive the tissue temperature signal and a fluid temperature signal generated from the temperature of the fluid, said processor comprising an alarm circuit for declaring the occurrence of an extravasation as a function of the tissue temperature signal and the fluid temperature signal, said processor coupled to said fluid temperature controller to control the temperature of the fluid so that a minimum difference exists between the tissue temperature and the fluid temperature.

35. The apparatus of claim 34 wherein said fluid temperature controller comprises a temperature sensor for sensing fluid temperature and generating the fluid temperature signal.

36. An apparatus for detecting extravasations in tissue injected with fluid, the apparatus comprising:

a fluid temperature sensor for sensing the temperature of fluid present in a fluid path element which transmits fluid to a patient, and generating a fluid temperature signal in response thereto;

a tissue temperature sensor for sensing the temperature of tissue proximate to the site of injection and generating a tissue temperature signal in response thereto; and

a processor adaptable to periodically receive said tissue temperature signal and said fluid temperature signal, said processor having an alarm circuit for declaring the occurrence of an extravasation and a threshold calculation circuit for periodically calculating at least one threshold value as a function of said tissue temperature signal, said fluid temperature signal and clinical experience based on one or more patients said processor activating said alarm circuit as a function of said tissue temperature signal said fluid temperature signal, and said at least one threshold value during a fluid injection.

37. The apparatus of claim 36, further comprising a user interface associated with said processor for allowing an operator to input patient parameters into the threshold calculation circuit, the patient parameters operable to modify the at least one threshold value.