Adaptive Surgical Tourniquet Apparatus and Method

• US 20080262533A1
• Filed: 04/19/2007
• Published: 10/23/2008
• Est. Priority Date: 04/19/2007
• Status: Active Grant

• Current Assignee: Western Clinical Engineering Ltd.
• Original Assignee: Western Clinical Engineering Ltd.
• Inventors: McEwen, James A., Jameson, Michael, Gebert, Michael A.
• Granted Patent: US 8,048,105 B2
• Time in Patent Office: Days
• US Class Current: 606/202
• CPC Class Codes: A61B 17/1355 Automated control means therefor

Abstract

An adaptive surgical tourniquet comprises: an inflatable cuff for encircling a limb of a patient; pressurizing means for pressurizing the cuff; pressure relief means for depressurizing the cuff; cuff pressure sensing means for sensing cuff pressure; limb occlusion pressure sensing means for sensing the patient'"'"'s initial limb occlusion pressure at a selected time; physiologic characteristic sensing means for sensing a physiologic characteristic of the patient; and pressure regulator means for establishing an adapted limb occlusion pressure that is a predetermined function of the initial limb occlusion pressure and the physiologic characteristic, wherein the pressure regulator means is operable after the initial limb occlusion pressure is sensed for selectably activating the pressurizing means and the pressure relief means to maintain the cuff pressure above the adapted limb occlusion pressure for a time period suitably long for the performance of a surgical procedure.

Claims

1. An adaptive surgical tourniquet, comprising:

an inflatable tourniquet cuff for encircling and applying a cuff pressure to a limb of a patient at a location;

pressure sensing means for sensing the cuff pressure;

physiologic characteristic sensing means for sensing a physiologic characteristic of the patient;

limb occlusion pressure means operable during a measurement time period for sensing arterial pulsations of blood flow in the limb distal to the location, for increasing the cuff pressure from a level near zero to a lowest level at which the arterial pulsations have a magnitude less than a minimum detection threshold, for producing an initial limb occlusion pressure indicative of the lowest level, and for decreasing the cuff pressure to a level near zero after the initial limb occlusion pressure has been produced; and

pressure regulator means operable after the measurement time period for establishing an adapted limb occlusion pressure that is a predetermined function of the initial limb occlusion pressure and the physiologic characteristic, wherein the pressure regulator means is further operable for maintaining the cuff pressure near a tourniquet reference pressure level.

2. The adaptive surgical tourniquet as defined in claim 1 wherein the tourniquet reference pressure level has a predetermined relationship to the adapted limb occlusion pressure.

3. The adaptive surgical tourniquet as defined in claim 1 wherein the tourniquet reference pressure level is equal to the sum of a first predetermined pressure level plus a second pressure level proportional to the adapted limb occlusion pressure.

4. The adaptive surgical tourniquet as defined in claim 1 wherein the pressure regulator means further produces an adapted limb occlusion pressure signal indicative of the adapted limb occlusion pressure, and including operator interface means responsive to the adapted limb occlusion pressure signal and operable for producing an indication perceptible to an operator of the adapted limb occlusion pressure and for enabling an operator to set the tourniquet reference pressure level.

5. The adaptive surgical tourniquet as defined in claim 1 wherein the physiologic characteristic is blood pressure and wherein the predetermined function is defined to be the initial limb occlusion pressure plus the difference between a first value of blood pressure estimated during the measurement time period and a second value of blood pressure estimated at a second time after the measurement time period.

6. The adaptive surgical tourniquet as defined in claim 1 wherein the physiologic characteristic is blood pressure and wherein the pressure regulator means further sets the tourniquet reference pressure level to the sum of a first predetermined pressure level plus a second pressure level proportional to the value of the adapted limb occlusion pressure at a selected time.

7. An adaptive surgical tourniquet, comprising:

an inflatable cuff for encircling a limb of a patient;

pressurizing means for pressurizing the cuff;

pressure relief means for depressurizing the cuff;

cuff pressure sensing means for sensing cuff pressure;

limb occlusion pressure sensing means for sensing the patient'"'"'s initial limb occlusion pressure at a selected time;

physiologic characteristic sensing means for sensing a physiologic characteristic of the patient; and

pressure regulator means for establishing an adapted limb occlusion pressure that is a predetermined function of the initial limb occlusion pressure and the physiologic characteristic, wherein the pressure regulator means is operable after the initial limb occlusion pressure is sensed for selectably activating the pressurizing means and the pressure relief means to maintain the cuff pressure above the adapted limb occlusion pressure for a time period suitably long for the performance of a surgical procedure.

8. The adaptive surgical tourniquet as defined in claim 7 wherein the limb occlusion pressure sensing means senses the patient'"'"'s initial limb occlusion pressure by measuring arterial pulsations of blood flow in the limb distal to the location, by increasing the cuff pressure from a level near zero to a lowest level at the selected time when the arterial pulsations have a magnitude less than a minimum detection threshold, by producing the initial limb occlusion pressure to be indicative of the lowest level, and by decreasing the cuff pressure upon production of the initial limb occlusion pressure.

9. The adaptive surgical tourniquet as defined in claim 7 wherein the physiologic characteristic is blood pressure and wherein the predetermined function is defined to be the initial limb occlusion pressure plus the difference between a first value of the blood pressure determined at the selected time and a second value of the blood pressure determined at a second time after the selected time.

10. The adaptive surgical tourniquet as defined in claim 7, wherein the pressure regulator means further maintains the cuff pressure near a tourniquet pressure level having a predetermined relationship to the adapted limb occlusion pressure.

11. The adaptive surgical tourniquet as defined in claim 7, wherein the pressure regulator means further maintains the cuff pressure near a tourniquet pressure level equal to the sum of a first predetermined pressure level plus a second pressure level proportional to the value of the adapted limb occlusion pressure.

12. The adaptive surgical tourniquet as defined in claim 7 wherein the physiologic characteristic is blood pressure, wherein the physiologic characteristic sensing means further senses a second physiologic characteristic of the patient, and wherein the pressure regulator means further establishes the adapted limb occlusion pressure to be a predetermined function of the initial limb occlusion pressure, the physiologic characteristic and the second physiologic characteristic.

13. An adaptive surgical tourniquet, comprising:

an inflatable cuff for encircling a limb of a patient;

pressurizing means for pressurizing the cuff;

pressure relief means for depressurizing the cuff;

cuff pressure sensing means for sensing cuff pressure;

limb occlusion pressure sensing means for sensing the patient'"'"'s initial limb occlusion pressure at a selected time;

physiologic characteristic sensing means for sensing a physiologic characteristic of the patient; and

pressure regulator means operable for establishing an adapted limb occlusion pressure that is a predetermined function of the initial limb occlusion pressure and the physiologic characteristic, for producing an adapted limb occlusion pressure signal indicative of the adapted limb occlusion pressure and further operable after the selected time for selectably activating the pressurizing means and the pressure relief means to maintain the cuff pressure near a tourniquet reference pressure level.

14. The adaptive surgical tourniquet as defined in claim 13 wherein the tourniquet reference pressure level has a predetermined relationship to the adapted limb occlusion pressure.

15. The adaptive surgical tourniquet as defined in claim 13 including operator interface means responsive to the adapted limb occlusion pressure signal and operable for producing an indication perceptible to an operator of the adapted limb occlusion pressure and for enabling an operator to set the tourniquet reference pressure level.

16. The adaptive surgical tourniquet as defined in claim 13 wherein the physiologic characteristic is indicative of blood pressure and wherein the predetermined function is defined to be the initial limb occlusion pressure plus the difference between a first indication of blood pressure at the selected time and a second indication of blood pressure at a second time after the selected time.

17. The adaptive surgical tourniquet as defined in claim 13 wherein pressure regulator means is further operable for selectably activating the pressurizing means and the pressure relief means to maintain the cuff pressure near the tourniquet reference pressure level over a time period suitably long for the performance of a surgical procedure.

18. The adaptive surgical tourniquet as defined in claim 17 further comprising recorder means for recording at least one value indicative of cuff pressure at a time within the time period.

19. A method of adapting the pressure applied to a patient'"'"'s limb by a surgical tourniquet cuff, comprising the steps of:

encircling a patient'"'"'s limb at a location with a cuff for applying a cuff pressure to the limb at the location;

sensing a physiologic characteristic of the patient;

sensing during a measurement time period arterial pulsations of blood flow in the limb distal to the location, increasing the cuff pressure from a level near zero to a lowest level at which the arterial pulsations have a magnitude less than a minimum detection threshold, producing an initial limb occlusion pressure indicative of the lowest level, and decreasing the cuff pressure to a level near zero after the initial limb occlusion pressure has been produced;

establishing after the measurement time period an adapted limb occlusion pressure that is a predetermined function of the initial limb occlusion pressure and the physiologic characteristic; and

maintaining the cuff pressure near a tourniquet reference pressure level having a predetermined relationship to the adapted limb occlusion pressure.

20. A method of adapting the pressure applied to a patient'"'"'s limb encircled by a surgical tourniquet cuff, comprising the steps of:

encircling a limb of a patient with a cuff for applying a cuff pressure to the limb;

sensing the patient'"'"'s initial limb occlusion pressure at a selected time;

sensing a physiologic characteristic of the patient;

establishing an adapted limb occlusion pressure that is a predetermined function of the initial limb occlusion pressure and the physiologic characteristic; and

beginning at a second time after the selected time and continuing for a time period suitably long for the performance of a surgical procedure, maintaining the cuff pressure above the adapted limb occlusion pressure by selectably pressurizing and depressurizing the cuff.

21. A method of adapting the pressure applied to a patient'"'"'s limb by a surgical tourniquet cuff, comprising the steps of:

encircling a limb of a patient with a cuff for applying a cuff pressure to the limb;

sensing the patient'"'"'s initial limb occlusion pressure at a selected time;

sensing a physiologic characteristic of the patient;

establishing an adapted limb occlusion pressure that is a predetermined function of the initial limb occlusion pressure and the physiologic characteristic;

producing an indication perceptible to an operator of the adapted limb occlusion pressure;

enabling an operator to set the tourniquet reference pressure level; and

maintaining the cuff pressure near the tourniquet reference pressure level by selectably pressurizing and depressurizing the cuff.

22. A surgical tourniquet system for establishing a patient'"'"'s limb occlusion pressure, comprising:

a controller connectable to a tourniquet and operable for regulating the pressure of a tourniquet;

a transducer connectable to a patient for measuring a patient'"'"'s blood flow, the transducer providing to the controller a blood flow signal representing the patient'"'"'s blood flow through the limb;

a monitor connectable to the patient for periodically detecting the value of the patient'"'"'s blood pressure and connected to the controller to provide to the controller a signal indicative of the detected values;

the controller including processing components for;

(a) establishing during an initial time period an initial limb occlusion pressure in part by changing the pressure in the tourniquet;

(b) determining an initial blood pressure value from detection of blood pressure during a time window that overlaps the initial time period; and

(c) determining subsequent to the initial time period an adapted limb occlusion pressure that is a function of the initial limb occlusion pressure and a difference between the initial blood pressure value and a blood pressure value detected subsequent to the determination of the initial blood pressure value.

23. The system of claim 22 wherein the initial blood pressure value is estimated from a blood pressure value that is detected during the time window.

24. The system of claim 22 wherein the initial blood pressure value is determined from two or more blood pressure values detected during the time window.

25. The system of claim 24 wherein the initial blood pressure value is determined by interpolation.

26. A method of controlling a surgical tourniquet system for establishing a patient'"'"'s limb occlusion pressure, comprising the steps of:

regulating the pressure of a tourniquet in response to a control signal;

measuring a patient'"'"'s blood flow and generating a blood flow signal representing the patient'"'"'s blood flow through the limb;

detecting the value of the patient'"'"'s blood pressure;

establishing during an initial time period an initial limb occlusion pressure;

determining an initial blood pressure value from detection of blood pressure during a time window that overlaps the initial time period; and

determining subsequent to the initial time period an adapted limb occlusion pressure that is a function of the initial limb occlusion pressure as well as a difference between the initial blood pressure value and a blood pressure value detected subsequent to the determination of the initial blood pressure value.

27. The method of claim 26 wherein the initial blood pressure value is estimated from a blood pressure value that is detected during the time window.

28. The method of claim 26 wherein the initial blood pressure value is determined from two or more blood pressure values detected during the time window.

29. The method of claim 28 wherein the initial blood pressure value is determined by interpolation.