Tourniquet Apparatus for Measuring Limb Occlusion Pressure

• US 20090124912A1
• Filed: 11/09/2007
• Published: 05/14/2009
• Est. Priority Date: 11/09/2007
• Status: Active Grant

• Current Assignee: Western Clinical Engineering Ltd.
• Original Assignee: Western Clinical Engineering Ltd.
• Inventors: McEwen, James A., Jameson, Michael, Gebert, Michael A., Cheung, William K.W.
• Granted Patent: US 8,425,426 B2
• Time in Patent Office: Days
• US Class Current: 600/495
• CPC Class Codes: A61B 17/135 inflatable for measuring blood pressure A61B5/022; inflatable pressure pads A61F5/34
• CPC Class Codes: A61B 17/1355 Automated control means therefor
• CPC Class Codes: A61B 5/02233 Occluders specially adapted therefor tourniquets A61B17/132
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• CPC Class Codes: A61B 5/0235 Valves specially adapted therefor
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B

Abstract

Improved tourniquet apparatus for measuring a patient'"'"'s limb occlusion pressure includes an inflatable tourniquet cuff for encircling a limb at a location and to which a tourniquet instrument is releasably connectable. The instrument includes pressure sensing for producing a cuff pressure signal indicative of the level of pressure in the cuff, a pressure regulation mechanism communicating with the cuff and responsive to the cuff pressure signal for moving fluid into and out of the cuff, thereby regulating the pressure in the cuff, a blood flow transducer for producing a blood flow signal indicative of blood flow past the cuff, and limb occlusion pressure means responsive to the blood flow signal and the cuff pressure signal for increasing the cuff pressure level until blood flow indicated by the blood flow signal decreases to a level less than a minimum detection threshold, and then suspending fluid movement into and out of the cuff to produce a limb occlusion pressure value that is indicative of a pressure in the cuff when the fluid motion is suspended.

Claims

1. Tourniquet apparatus for measuring a patient'"'"'s limb occlusion pressure comprising:

an inflatable tourniquet cuff for encircling a limb at a location;

a tourniquet instrument releasably connectable to the cuff and including

pressure sensing means for producing a cuff pressure signal indicative of the level of pressure in the cuff,

pressure regulation means communicating with the cuff and responsive to the cuff pressure signal for moving fluid into and out of the cuff, thereby regulating the pressure in the cuff,

blood flow transducing means for producing a blood flow signal indicative of blood flow past the cuff, and

limb occlusion pressure means responsive to the blood flow signal and the cuff pressure signal for increasing the cuff pressure level until blood flow indicated by the blood flow signal decreases to a level less than a minimum detection threshold, and then suspending fluid movement into and out of the cuff to produce a limb occlusion pressure value that is indicative of a pressure in the cuff when the fluid motion is suspended.

2. The tourniquet apparatus as defined in claim 1 wherein the limb occlusion pressure means is further operable for detecting arterial pulsations of blood flow and wherein the limb occlusion pressure means increases the cuff pressure level in synchrony with the detected arterial pulsations.

3. The tourniquet apparatus as defined in claim 2 wherein the limb occlusion pressure means increases the cuff pressure level in synchrony with a selected arterial pulsation from a first level to a second level that is equal to the sum of the cuff pressure level indicated by the cuff pressure signal at the time of the selected arterial pulsation plus an incremental pressure level.

4. The tourniquet apparatus as defined in claim 1 wherein the blood flow transducing means is adapted for applying to a portion of the limb distal to the cuff and wherein the blood flow signal is indicative of blood flow past the cuff and into the portion.

5. The tourniquet apparatus as defined in claim 4 wherein the blood flow transducing means includes blood flow quality means carried on the blood flow transducing means for producing an indication perceptible to an operator if the quality of the detected blood flow is less than a predetermined minimum quality when the cuff pressure level is near zero.

6. The tourniquet apparatus as defined in claim 4 wherein the blood flow transducing means includes blood flow quality means carried on the blood flow transducing means for producing an indication perceptible to an operator if the blood flow is below a predetermined minimum level when the cuff pressure level is near zero.

7. The tourniquet apparatus as defined in claim 1 wherein the blood flow transducing means is further adapted for applying to a portion of the limb distal to the cuff, wherein the blood flow signal is indicative of blood flow in the portion, wherein the limb occlusion pressure means is further operable for detecting arterial pulsations of blood flow in the portion, and wherein the blood flow transducing means includes blood flow quality means carried on the blood flow transducing means for producing an indication perceptible to an operator if the magnitude of the arterial pulsations is not greater than a predetermined minimum level when the cuff pressure level is near zero.

8. Tourniquet apparatus for measuring a patient'"'"'s limb occlusion pressure comprising:

an inflatable tourniquet cuff for encircling a limb at a location;

a tourniquet instrument releasably connectable to the cuff and including

pressure sensing means for producing a cuff pressure signal indicative of the level of pressure in the cuff,

pressure regulation means communicating with the cuff and responsive to the cuff pressure signal for regulating the pressure in the cuff near a reference pressure level,

blood flow transducing means adapted for applying to a portion of the limb distal to the cuff to produce a blood flow signal indicative of blood flow in the portion, and including blood flow quality means carried on the blood flow transducing means for producing an indication perceptible to an operator if the blood flow is less than a predetermined blood flow quality level when the reference pressure level is near zero; and

limb occlusion pressure means responsive to the blood flow signal and the cuff pressure signal and operable for producing a limb occlusion pressure value indicative of the lowest level of pressure in the cuff at which the blood flow is less than a minimum detection threshold.

9. The tourniquet apparatus as defined in claim 8 wherein the limb occlusion pressure means is further operable for detecting arterial pulsations of blood flow in the portion, and wherein the blood flow quality means produces the indication perceptible to the operator if the magnitude of the arterial pulsations is not greater than the predetermined blood flow quality level.

10. The tourniquet apparatus as defined in claim 8 and including operator key means carried on the blood flow transducing means, wherein the operator key means is adapted to enable the operator to initiate operation of the limb occlusion pressure means if the blood flow is at least equal to the predetermined blood quality flow level.

11. The tourniquet apparatus as defined in claim 10 wherein the operator key means is further adapted to prevent the operator from initiating operation of the limb occlusion pressure means if the blood flow is less than the predetermined blood flow quality level.

12. Tourniquet apparatus for measuring a patient'"'"'s limb occlusion pressure comprising:

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

pressure sensing means for producing a cuff pressure signal indicative of the level of pressure in the cuff;

pressure regulation means communicating with the cuff and responsive to the cuff pressure signal for regulating the pressure in the cuff near a reference pressure level;

blood flow transducing means adapted for producing a blood flow signal indicative of blood flow past the cuff;

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

limb occlusion pressure means responsive to the blood flow signal and the cuff pressure signal and operable for producing a limb occlusion pressure value indicative of the lowest level of pressure in the cuff at which the blood flow is less than a minimum detection threshold and further operable for recording a first level of the physiologic characteristic corresponding to the time when the blood flow is less than the minimum detection threshold; and

safety margin indicator means responsive to the reference pressure level for producing a safety margin value having a predetermined relationship to the reference pressure level, the limb occlusion pressure value, the recorded first level of the physiologic characteristic and to a second level of the physiologic characteristic.

13. The tourniquet apparatus as defined in claim 12 wherein the predetermined relationship is set to be equal to the sum of a first margin plus a second margin, wherein the first margin is equal to the reference pressure level minus the limb occlusion pressure value, and wherein the second margin is a predetermined function of the recorded first level of the physiologic characteristic minus the second level of the physiologic characteristic.

14. The tourniquet apparatus as defined in claim 13 wherein the physiologic characteristic is systolic blood pressure, wherein the predetermined function is equal to a second margin multiplied by a predetermined value, and wherein the second margin is equal to the recorded first level of the physiologic characteristic minus the second level.

15. The tourniquet apparatus as defined in claim 12 and including operator interface means adapted for indicating the safety margin value in a form perceptible to an operator and further adapted for enabling the operator to change the reference pressure level to a desired level.

16. The tourniquet apparatus as defined in claim 15 wherein the safety margin indicator means includes means for setting a safety margin alarm limit window at predetermined levels above and below the first margin, and wherein the operator interface means is further adapted to produce a further indication to the operator when the safety margin value is outside the window.

17. Tourniquet apparatus for measuring a patient'"'"'s limb occlusion pressure comprising:

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

pressure sensing means for producing a cuff pressure signal indicative of the level of pressure in the cuff;

pressure regulation means communicating with the cuff and responsive to the cuff pressure signal for regulating the pressure in the cuff near a reference pressure level;

blood flow transducing means adapted for producing a blood flow signal indicative of blood flow past the cuff;

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

limb occlusion pressure means responsive to the blood flow signal and the cuff pressure signal and operable for suspending communication between the pressure regulation means and the cuff near a first time when the blood flow decreases from a level greater than a minimum detection threshold to a level less than the minimum detection threshold, for producing a limb occlusion pressure value indicative of the pressure in the cuff while the communication is suspended, and for recording a level of the physiologic characteristic near the first time; and

safety margin indicator means responsive to the reference pressure level for producing a safety margin value having a predetermined relationship to the reference pressure level, the limb occlusion pressure value, the recorded level of the physiologic characteristic and a second level of the physiologic characteristic at a second time after the first time.

18. A method of determining for a patient a recommended tourniquet pressure based upon the occlusion pressure of a limb to which an inflatable and deflatable cuff is attached;

comprising the steps of;

directing through a port in the cuff the flow of fluid into the cuff in order to inflate and pressurize the cuff;

while

monitoring blood flow in the limb to determine an instance when arterial blood flow past the cuff is substantially occluded;

preventing inflation and deflation of the cuff at that instance;

while

measuring the cuff pressure to establish an initial limb occlusion pressure level; and

calculating the recommended tourniquet pressure as the sum of the initial limb occlusion pressure level and a safety margin level.

19. The method of claim 18 including the step of occasionally updating the initial limb occlusion pressure level and safety margin level based upon changes in the patient'"'"'s physiology.

20. The method of claim 19 including the step of producing an alarm signal when the updated safety margin level is outside of a predetermined range.

21. The method of claim 18 wherein the monitoring step includes attaching a blood flow transducer to a portion of the limb and equipping the transducer with an indicator for producing two signals when a predetermined minimal amount of blood is and is not, respectively, flowing in the portion of the limb.

22. The method of claim 21 being initiated by a controller, the method further comprising the step of

equipping the transducer with a key that operable for signaling the controller to initiate the method of determining the recommended tourniquet pressure.

23. The method of claim 22 including the step of enabling and disabling the operation of the key depending upon the signal produced by the indicator.

24. The method of claim 21 including the step of initializing the blood flow transducer to confirm the transducer is attached to the limb portion.

25. The method of claim 21 including the step of initializing the blood flow transducer to confirm the transducer is unaffected by ambient light above a predetermined threshold level.