How can variable-fit contour cuffs improve tourniquet safety and effectiveness?

The primary function of a tourniquet cuff is to efficiently apply pneumatic pressure in the cuff to tissues in the underlying limb. If this is done most efficiently, then pneumatic tourniquet pressure can be minimized, thus reducing the risk of injuries. It is clearly established in the surgical literature that higher tourniquet pressures are associated with higher probabilities of injury ^[1-3].

Efficient application of cuff pressure to the limb requires that the cuff be in close contact with the limb across the entire width of the cuff, from the proximal to the distal cuff edges. This in turn means that the cuff shape must match the limb shape. Unfortunately, standard cylindrical tourniquet cuffs are ideally suited for application only to patients with cylindrical limbs (For details, see Tourniquet Cuff Selection Guide). When applied to a contoured or tapered limb, a cylindrical cuff will not optimally match the patient’s limb shape, and that mis-match typically results in a snug fit at the proximal edge and a looser fit at the distal edge. This mis-match does not allow pressure to be applied to the limb most efficiently, from proximal to distal cuff edges. Consequently, on a contoured limb, a cylindrical cuff may prove unable to achieve a bloodless field distal to the cuff at a “normal” tourniquet pressure, or alternatively a higher tourniquet pressure may be required to achieve a bloodless field.

Also, if a cylindrical tourniquet cuff is applied to a contoured or tapered limb and inflated, it may have a tendency to roll or slide distally on the contoured limb during a surgical procedure. This may affect the ability of the cuff to stop blood flow, and may lead to high pressure gradients at the distal cuff edge, a hazard that may lead to nerve injury.

In an effort to better match the contoured shape of a patient’s limb at a desired cuff location, contour cuffs were developed. Some contour cuffs only fit one type of contoured limb shape. This is as undesirable as trying to fit a cylindrical cuff to all limb shapes. Other types of contour cuffs, called variable-fit contour cuffs, can adapt to limbs having different shapes. They can fit (or match) a wide range of limbs well, ranging from limbs that are almost cylindrical in shape to limbs that are highly contoured or tapered. Variable-fit contour cuffs apply pneumatic cuff pressure efficiently to underlying limbs having a wide range of non-cylindrical shapes. It has been shown in the surgical literature that wide variable-contour cuffs substantially reduce tourniquet pressures required to create a bloodless surgical field distal to the inflated cuff ^[4-5].

Variable-fit contour cuffs also improve tourniquet safety by incorporating structural improvements and a much improved fastening elements have been introduced ^[6-11]. These fasteners incorporate pivoting securing straps which allow the cuff to adapt and match the shape of limbs of different shapes and sizes, while at the same time allowing the cuff to be secured by dual independent fasteners for improved safety. This design consistently allows the cuff to fit uniformly onto limbs having a wide range of limb contours, tapers and sizes. This close shape match is not possible with cylindrical tourniquet cuffs, nor is it possible with non-variable contour cuffs (For details, see Tourniquet Cuff Selection Guide).

In combination with techniques described in the medical literature that are based on measuring the Limb Occlusion Pressure (LOP) of individual patients, the enhanced shape-matching possible with variable-fit contour cuffs allows for much lower tourniquet pressures to be used to establish and maintain a bloodless surgical field ^[12]. As noted in the surgical literature, lower tourniquet pressures and lower pressure gradients at cuff edges are associated with lower probabilities of patient injury.

References for educational viewing only

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[1] Ochoa J, et al. "Anatomical changes in peripheral nerves compressed by a pneumatic tourniquet". Journal of Anatomy. 113 (1972): 433-455. [2] Gilliatt R and Ochoa J. The cause of nerve damage in acute compression. Trans Am Neurol Ass 1974: 99: 71-4. [3] Shaw J and Murray D. The relationship between tourniquet pressure and underlying soft tissue pressure in the thigh. J Bone Joint Surg 1982: 64A(8):1148-52. [4] McEwen JA, Kelly DL, Jardanowski T, Inkpen K. "Tourniquet safety in lower leg applications." Orthopaedic Nursing, 21(5) (2002): 55-62. [5] Younger A, McEwen JA, Inkpen K. "Wide contoured thigh cuffs and automated limb occlusion measurement allow lower tourniquet pressures." Clinical Orthopaedics and Related Research, 428 (2004): 286-93. [6] McEwen, James A. United States Patent No. 5,312,431, May 17, 1994, "Occlusive Cuff" (plus associated foreign patents). [7] McEwen, James A. United States Patent No. 5,454,831, October 3, 1995, "Occlusive Cuff System." [8] McEwen, James A. United States Patent No. 5,578,055, November 26, 1996, "Occlusive Cuff" (plus associated foreign patents). [9] McEwen, James A. United States Patent No. 5,649,954, July 22, 1997, "Tourniquet Cuff System." [10] McEwen, James A. United States Patent No. 5,741,295, April 21, 1998, "Overlapping Tourniquet Cuff System." [11] McEwen, James A. et al. United States Patent Application 20070219580, September 20, 2007, "Low-cost contour cuff for surgical tourniquet systems." [12] Reilly et al. "Minimizing Tourniquet Pressure in Pediatric Anterior Cruciate Ligament Reconstructive Surgery. A Blinded, Prospective Randomized Controlled Trial." Journal of Pediatric Orthopaedics, 29 (2009): 275-280.