Surgical tourniquet

Surgical tourniquets prevent blood flow to a limb and enable surgeons to work in a bloodless operative field. This allows surgical procedures to be performed with improved precision, safety and speed. Tourniquets are widely used in orthopedic and plastic surgery, as well as in intravenous regional anesthesia (Bier block anesthesia) where they serve the additional function of preventing local anesthetic in the limb from entering general circulation.

In the early 1980s, microprocessor-controlled pneumatic tourniquets were invented by Dr James McEwen, PhD ^[1][2]. Automatic tourniquets based on this invention are now standard equipment in operating rooms worldwide, and these systems have significantly improved safety and convenience of tourniquet use.

Despite many advances in tourniquet technology, tourniquet related injuries continue to be of concern^[3]. High pressures under a tourniquet cuff can cause nerve, muscle and skin injury. Minimizing tourniquet pressure, reducing inflation time and using a microprocessor-controlled pneumatic tourniquet, which allows pressure to be accurately monitored and controlled, reduce the risk of tourniquet related injury.

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Surgical tourniquet equipment

Modern pneumatic tourniquets have three basic components: an inflatable cuff, a compressed gas source, and an instrument which automatically monitors and controls cuff pressure. The cuff is secured around the limb proximal to the operative site. Pressure is exerted on the circumference of the limb by means of compressed gas which is introduced into the tourniquet cuff by a microprocessor-controlled source, via connection tubing. When sufficient pressure is exerted, vessels and arteries beneath the cuff become temporarily occluded, preventing blood flow past the cuff. While the cuff is inflated, the tourniquet system automatically monitors and maintains pressure as chosen by the user. Cuff pressure and inflation time are displayed, and an audiovisual alarm alerts the user to alarm conditions, such as a cuff leak, if present.

Contoured cuffs

Studies have shown that tourniquet cuff pressures can be substantially reduced without compromising the quality of surgical field by using wide, contoured cuffs.^[4] Wide cuffs also reduce the risk of injury to underlying tissue by dispersing the cuff’s force over a greater surface area. Standard cuffs are relatively narrow in width and are cylindrical in shape. Where there is a significant difference in limb circumference between the distal and proximal edges of the cuff, a contoured cuff with a tapered, conical shape provides a more anatomical fit and maximizes the contact area between cuff and limb. Further, wide cuffs with an adjustable, variable taper have recently been introduced, permitting one cuff to conform to a variety of limb shapes^[5].

Limb occlusion Ppressure

Limb occlusion pressure (LOP) is the minimum tourniquet pressure required to occlude blood flow to a specific patient's limb at a specific time and accounts for a patient’s limb and vessel characteristics, and the type and fit of the cuff. LOP can be determined by gradually increasing tourniquet pressure until distal arterial pulses cease, as indicated by a device sensing blood flow, such as a Doppler stethoscope. Studies have shown that cuff pressure based on LOP measured immediately prior to surgery is generally lower than commonly used cuff pressures and is sufficient to maintain a satisfactory surgical field^[6]. Traditionally this method has not been used due to its time consuming and technically demanding nature. However, a pneumatic tourniquet that uses an automated plethysmographic system to calculate LOP in approximately 30 seconds at the beginning of surgery has recently been developed^[7]. This device has similar accuracy to the standard Doppler technique and addresses the practicality of using such a technique in the OR.

Limb protection

For some cuffs, a matching limb protection sleeve is available to help protect soft tissues under the cuff^[5][8]. Without proper protection, underlying soft tissue is prone to damage from wrinkling, pinching or shearing^[9]. Sleeves are sized according to the cuff width and the patient’s limb circumference. They are intended to fit snugly and to extend beyond the edge of the cuff, to ensure no direct contact between cuff and skin. Sleeve materials that do not shed loose fibers are chosen to avoid lint becoming trapped in the cuff’s hook and loop fasteners, which reduces their effectiveness.

References