© Copyright, 2014, J.A. McEwen
Last updated February 2014

How are advances improving safety, accuracy, and reliability?

Elements included in modern surgical tourniquet systems have resulted in substantially increased safety, accuracy and reliability. The widespread adoption and use of such automatic tourniquets employing microprocessor technology, together with improved designs of pneumatic tourniquet cuffs, has greatly improved the safety, accuracy and reliability of tourniquets in surgery. The resulting decrease in the number of reported hazards and incidents was accompanied in 1996 by the (US) FDA classification of pneumatic tourniquets as Class I medical devices (indicating that they present minimal harm to the user and do not present a reasonable source of injury through normal use), and the FDA thereafter exempted pneumatic tourniquets from its (510k) pre-market notification and clearance procedures. Modern pneumatic tourniquets are used in an estimated 15,000 orthopaedic and non-orthopaedic surgical procedures daily in the US and elsewhere, facilitating surgery by reliably establishing a bloodless surgical field with relative safety.

The modern microcomputer-based tourniquet system was invented in 1981 by McEwen[1]. These new automated surgical tourniquet systems incorporated a number of improvements which resulted in better patient safety, greater accuracy of pressure regulation and greater reliability. For example, earlier surgical tourniquets relied on mechanical pressure regulators that were inherently less accurate, they lacked any audiovisual alarms to promptly warn users of hazardously high and low pressures in tourniquet cuffs, they lacked automatic timers and elapsed time alarms, and they lacked self-test apparatus to automatically check the tourniquet instrument at startup and prior to patient use. All of these limitations were overcome by the introduction of the first automatic tourniquet systems in 1981, and their subsequent acceptance and use in orthopaedics and other surgical specialties has been widespread.

 
Fig. 1 Block diagram of elements of a modern tourniquet system
 

Since 1981, additional improvements to automatic tourniquet systems have been made to further increase patient safety, tourniquet accuracy and tourniquet reliability. The major improvements are shown in Fig. 1: a microcomputer-controlled pressure regulator typically maintains cuff pressure within one percent of set pressure, and an automatic timer provides an accurate record of tourniquet inflation time; audiovisual alarms are often included to promptly alert an operator if hazardously high or low cuff pressures are present; automatic detection and monitoring of potentially hazardous air leakage from pressurized tourniquet cuffs is often included[1,2]; self-test capabilities are typically included to provide for automatic checks of calibration, audiovisual alarms, and hardware and software integrity at each startup of the tourniquet instrument[2,3]; and backup power is often included to allow such instruments to continue normal operation in the event of an unanticipated power interruption. More recent generations of automatic tourniquet systems have included non-volatile memory to enable surgical staff to store specialized settings most appropriate for certain patients, for example in paediatric and hand surgery, and the same memory can be used to store relevant data about significant surgical events related to tourniquet usage, to enable a data printout or transfer to an operating room information network[4].

Additional safety features of some modern tourniquet systems include cuff a cuff hazard interlock to help a user from inadvertently powering off a tourniquet instrument during usage[5], and an IVRA safety interlock to help prevent a user from inadvertently deflating an incorrect cuff during IVRA (Bier’s block anaesthesia) and bilateral limb procedures[6]. Most recently, modern tourniquet systems have included automatic means of estimating the Limb Occlusion Pressure (LOP) of each patient, permitting individualized setting of safer tourniquet pressures as described below[7]. To faciliitate LOP measurement and adaptation of tourniquet operation during surgery, some modern tourniquet systems include provision for connection of the tourniquet instrument to physiologic monitors[2,8]. Modern tourniquet systems are also becoming more integrated with a wide range of pneumatic cuffs that are connectable to them, to optimize the performance of the overall system for greatest safety, accuracy and reliability[9-11].

References for educational viewing only

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  [1] McEwen J. Complications of and improvements in pneumatic tourniquets used in surgery. Medical Instrumentation 1981;15(4): 253-7.

[2] McEwen, James A. United States Patent No. 4,479,494, October 30, 1984, "Adaptive Pneumatic Tourniquet" (plus associated foreign patents).

[3] McEwen, James A. United States Patent No. 4,469,099, September 4, 1984, "Pneumatic Tourniquet."

[4] McEwen, James A., et al., United States Patent No. 5,607,447, March 4, 1997, "Physiologic Tourniquet."

[5] McEwen, James A. United States Patent No. 6,213,939, April 10, 2001, "Hazard Monitor for Surgical Tourniquet Systems."

[6] McEwen, James A. and M. Jameson. U.S. Patent No. 5,556,415, September 17, 1996, "Physiologic Tourniquet for Intravenous Regional Anesthesia".

[7] McEwen, JA, et al., United States Patent No. 7,479,154, Jan 20, 2009, "Surgical tourniquet apparatus for measuring limb occlusion pressure."

[8] McEwen JA, McGraw RW. "An adaptive tourniquet for improved safety in surgery." IEEE Trans Bio - Med Eng 29 (1982): 122-8.

[9] McEwen, James A. et al., United States Patent Application 20080262533, October 23, 2008, "Adaptive Surgical Tourniquet and Method."

[10] McEwen, James A. et al., United States Patent Application 20070032818, Feb 8, 2007, "Surgical tourniquet cuff for limiting usage to improve safety."

[11] McEwen, James A. et al., United States Patent Application 20070135836, June 14, 2007, "Low-cost disposable tourniquet cuff."

© Copyright, 2014, J.A. McEwen
Last updated February 2014
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