Surgical Tourniquet Instrument Technology

What is the purpose of a surgical tourniquet instrument?

The purpose of a surgical tourniquet instrument is to safely and accurately supply and regulate the pressure in a tourniquet cuff.

Personalized surgical tourniquet instruments:

Personalized tourniquet instruments are state-of-the-art, modern pneumatic tourniquet instruments. Click here to learn about the history of tourniquets. They include automatic means of estimating the Limb Occlusion Pressure (LOP) of each patient, permitting individualized setting of safer and lower tourniquet pressures [1]. Click here to find out how Limb Occlusion Pressure (LOP) minimizes cuff pressure and increases patient safety. Personalized tourniquet instruments have an intuitive user interface; accurate and automatic pressure control for one or more pneumatic channels; audiovisual alarms; and numerous features to improve usability, reduce errors and ultimately increase patient safety. To facilitate LOP measurement and adaptation of tourniquet operation during surgery, some personalized tourniquet instruments include provision for connection of the tourniquet instrument to physiologic monitors [2, 3]. Personalized tourniquet instruments 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 [4-6]. Figure 1 shows elements of a personalized tourniquet system.

The user interface, pressure control, and safety features of a typical personalized tourniquet instrument are outlined below.

User interface

Personalized tourniquet instruments have digital displays and easy-to-use user interfaces. Typically, the tourniquet instrument allows the perioperative staff to set the tourniquet pressure, inflate or deflate the tourniquet cuff, and adjust safety settings such as the maximum allowed pressure and time limits. The digital display and control buttons give the surgical staff a straightforward method of monitoring the tourniquet pressure and time, and for changing the various tourniquet settings. Personalized tourniquet instruments have non-volatile memory to enable surgical staff to store specialized settings most appropriate for certain surgeries (e.g. paediatric and hand surgery), relevant data about significant surgical events related to tourniquet usage, and to enable a data printout or transfer to an operating room information network. In addition, personalized tourniquet instruments use intuitive audio-visual alarms to alert the surgical staff of events related to patient safety.

Pressure control

Compressed gas source

The tourniquet cuff bladder requires a source of compressed gas to supply a carefully controlled amount of tourniquet pressure. The gas used may be ambient air, nitrogen, or some other gas. Most modern tourniquet systems utilize low-pressure gas provided by pumps, while a few systems use high-pressure gas sources. Note that nitrous oxide or oxygen should never be used to inflate the tourniquet cuff, because of the increased risk of fire.

Personalized tourniquet systems utilize an internal electrical pump to compress ambient air to a low pressure; these systems do not require external high-pressure sources, such as portable canisters, portable tanks, or built-in hospital systems.

Pressure regulator

The pressure regulator adjusts and controls the gas pressure in the cuff bladder. Older, non-computerized tourniquet systems utilize valves that attempt to respond mechanically to changes in pressure. For example, if pressure in the cuff bladder falls, a valve may open to allow more gas to enter the regulator from the gas source; if pressure exceeds a certain level, the pressure may force a release valve to open and expel gas into the environment. Sometimes, the pressure levels at which these two valves turn on and off are quite different and cuff pressure may fluctuate within a certain range above and below the selected pressure. Due to the sensitive mechanical components of these systems, it is very important to follow the manufacturer’s instructions regarding frequent testing, and calibration and to perform these checks before each surgical procedure as recommended. In general, tourniquet systems with mechanical regulators are now considered to be inaccurate, unreliable, and are not suitable for incorporation with modern tourniquet safety features.

In personalized tourniquet instruments, the internal electrical pump, pressure display, and pressure regulator are combined in a single instrument in which a microprocessor continuously monitors and compensates for changing levels of pressure in the cuff bladder. Regulation does not rely on mechanical (pressure) forces to turn valves off and on. Instead, the microprocessor can detect extremely small changes in the cuff pressure and automatically regulate the flow of gas to control the pressure. Typical surgical-grade pressure regulators can accurately autoregulates cuff pressure to be less than 15 mmHg different than the target pressure during a 1 second period [7, 8].

Some personalized tourniquet systems use a sophisticated “dual-port” system which gives the most accurate control of cuff pressure and the fastest response to pressure changes. In a dual-port system, each cuff bladder has two ports and is connected to the personalized instrument using two hoses. One port is for monitoring the pressure (“sensing port”); the other port is for inflating and deflating the cuff and for automatically supplying and releasing small amounts of gas during use to control cuff pressure (“supply port”). In some more basic systems, a single port performs both functions for each cuff bladder. Single-port tourniquet systems are less accurate than dual-port tourniquet systems.

Personalized Pressures

Many studies published in the medical literature have shown that higher tourniquet pressures and pressure gradients are associated with higher risks of tourniquet-related injuries [9-15].  The safest tourniquet pressure is the lowest pressure that will stop the flow of arterial blood past a specific cuff applied to a specific patient for the duration of that patient’s surgery [9, 16, 17]. Personalized tourniquet instruments reduce the risk of tourniquet-related injuries by enabling the application of lower tourniquet pressures and pressure gradients to the patient.  This is accomplished by the instrument automatically measuring each patient’s Limb Occlusion Pressure (LOP) and recommending a tourniquet pressure based on LOP. LOP can be defined as the minimum pressure required, at a specific time in a selected tourniquet cuff applied to an individual patient’s limb at a desired location, to stop the flow of arterial blood into the limb distal to the cuff [4]. Click here to learn more about how a tourniquet pressure based on LOP reduces risk of tourniquet-related injuries.

Safety Features

Below is a list of safety features found in the most advanced tourniquet instruments [2, 18-22]:

• Automatic measurement of the Limb Occlusion Pressure (LOP) to enable individualized setting of safer and lower tourniquet pressures
• Self-calibration to establish correct pressure readings
• Self-check to make sure the system is operational prior to use
• Ability to set the maximum tourniquet pressure and inflation time limits
• Automatic timer to provide an accurate record of tourniquet inflation time
• Backup battery to allow the instrument to continue to operate during an unanticipated power interruption or during patient transport
• A cuff hazard interlock to avoid inadvertent power off of the instrument while a cuff is still inflated
• Interlocks to help prevent unintended cuff deflation during IVRA procedures and bilateral limb procedures. Click here to find out more about Intravenous Regional Anesthesia
• Positive-locking ports to ensure complete pneumatic link with the pneumatic tubing and to prevent accidental disconnections
• Interfaces to information systems in the operation room to remotely capture cuff pressures, inflation times and potentially hazardous events, and
• Audio-visual alarms for:
  • Reaching the maximum pressure,
  • Reaching the maximum inflation time,
  • Low cuff pressure,
  • High cuff pressure,
  • Occlusion in the pneumatic system,
  • Leakage in the pneumatic system,
  • Low battery, and
  • Failure of the cuff to depressurize when deflation is intended.

Sources:

[1] McEwen JA, Jameson M, Upward A, inventors; Mcewen James A, assignee. Surgical tourniquet apparatus for measuring limb occlusion pressure. United States patent US 7,479,154. 2009 Jan 20.

[2] McEwen JA, Jameson M, Gebert MA, inventors; Western Clinical Engineering Ltd., assignee. Adaptive surgical tourniquet apparatus and method. United States patent US 8,048,105. 2011 Nov 1.

[3] McEwen JA, McGraw RW. An adaptive tourniquet for improved safety in surgery. IEEE Transactions on Biomedical Engineering. 1982 Feb(2):122-8.

[4] McEwen JA, inventor; Western Clinical Engineering Ltd., assignee. Adaptive pneumatic tourniquet. United States patent US 4,479,494. 1984 Oct 30.

[5] McEwen JA, Jameson M, inventors; Western Clinical Engineering, Ltd, assignee. Surgical tourniquet cuff for limiting usage to improve safety. United States patent US 7,955,352. 2011 Jun 7.

[6] McEwen JA, Jameson M, Glinz KL, Upward AJ, inventors; Western Clinical Engineering, Ltd, assignee. Low-cost disposable tourniquet cuff apparatus and method. United States patent US 8,137,378. 2012 Mar 20.

[7] Zimmer A.T.S. 4000TS Operator / Service Manual Revision: E.

[8] Delfi PTS ii Personalized Tourniquet System Operator & Maintenance Manual.

[9] Noordin S, McEwen JA, Kragh Jr CJ, Eisen A, Masri BA. Surgical tourniquets in orthopaedics. JBJS. 2009 Dec 1;91(12):2958-67.

[10] Murphy C, Winter D, Bouchier-Hayes D. Tourniquet injuries: pathogenesis and modalities for attenuation. Acta orthopaedica belgica. 2005 Dec;71(6):635.

[11] McGraw RW, McEwen JA, McFarlane RM. The tourniquet. Unsatisfactory results in hand surgery. New York: Churchill Livingstone. 1987:5-13.

[12] Ochoa J, Fowler TJ, Gilliatt RW. Anatomical changes in peripheral nerves compressed by a pneumatic tourniquet. Journal of Anatomy. 1972 Dec;113(Pt 3):433.

[13] Gilliatt RW, Ochoa J, Rudge P, Neary D. The cause of nerve damage in acute compression. Trans Am Neurol Assoc. 1974;99:71-4.

[14] McEwen J, Casey V. Measurement of hazardous pressure levels and gradients produced on human limbs by non-pneumatic tourniquets. In: Proceedings of the 32nd Conference of the Canadian Medical and Biological Engineering Society 2009. Calgary, Canada; 2009 May 20-22. p 1-4.

[15] Graham B, Breault MJ, McEwen JA, McGraw RW. Perineural pressures under the pneumatic tourniquet in the upper extremity. The Journal of Hand Surgery: British & European Volume. 1992 Jun 1;17(3):262-6.

[16] Olivecrona C, Ponzer S, Hamberg P, Blomfeldt R. Lower tourniquet cuff pressure reduces postoperative wound complications after total knee arthroplasty. J Bone Joint Surg Am. 2012 Dec 19;94(24):2216-21.

[17] Estebe JP, Le Naoures A, Chemaly L, Ecoffey C. Tourniquet pain in a volunteer study: effect of changes in cuff width and pressure. Anaesthesia. 2000 Jan 1;55(1):21-6.

[18] Jeyasurya J, Jameson M, Glinz K, Sadr Hooman, Day B, Masri B, McEwen J. Current concepts in tourniquets. CMBES Proceedings. 2014 May.

[19] McEwen JA, inventor; Western Clinical Engineering Ltd., assignee. Pneumatic torniquet. United States patent US 4,469,099. 1984 Sep 4.

[20] McEwen JA, inventor; Mcewen James Allen, assignee. Hazard monitor for surgical tourniquet systems. United States patent US 6,213,939. 2001 Apr 10.

[21] McEwen JA, Jameson M, inventors; Mcewen, James A., Jameson, Michael, assignee. Physiologic tourniquet for intravenous regional anesthesia. United States patent US 5,556,415. 1996 Sep 17.

[22] McEwen JA, Jameson M, Gebert MA, Cheung WK, inventors; Western Clinical Engineering Ltd., assignee. Apparatus and method for estimating leakage in a surgical tourniquet system. United States patent US 8,083,763. 2011 Dec 27.