J Am Coll Surg. 2018 Sep;227(3):332-345

# From pull to pressure: effects of tourniquet buckles and straps.

Valliere M, Wall P, Buising C

BACKGROUND: Limb tourniquet pressures > 100 mmHg before tightening system use eases achieving arterial occlusion, minimizes tightening system problems, and probably minimizes discomfort. This study examined effects of buckle and strap features on converting pulling force to strap pressure.

STUDY DESIGN: Twenty-two buckle and strap combinations were evaluated using a thigh-diameter, ballistic gel cylinder and 3 thighs. Weights of 14.11, 27.60, and 41.11 kg provided pulling force. The contribution of buckle movement was evaluated: all buckles on gel and 12 on thighs allowed limited vertical movement, 12 on gel and 4 on thighs held static.

RESULTS: Force conversion patterns per combination were similar on gel and thighs, including greatest force conversion with some buckle movement allowed. Smooth, round redirect buckles without engagement of a strap-securing mechanism had the best conversions of pulling force to tourniquet pressure; 2 achieved arterially occlusive pressures, neither commercially available. Among hook-and-loop secured tourniquets and threaded for self-securing tourniquets, the Generation 7 Combat Application Tourniquet (C-A-T7) and the Tactical Ratcheting Medical Tourniquet (Tac RMT) had the best conversions of pull to pressure (thigh applications/each weight, mean ± SD: C-A-T7 91 ± 11, 164 ± 30, 228 ± 34 mmHg; Tac RMT 82 ± 13, 150 ± 16, 222 ± 17 mmHg). Other Ratcheting Medical Tourniquets with the same buckle but different strap fabrics performed less well. Even lower pressures occurred with the Tactical Mechanical Tourniquet, the Special Operations Forces Tactical Tourniquet, the Parabelt, and the SAM XT Extremity Tourniquet (165 ± 11, 178 ± 13, 131 ± 14, and 106 ± 14 mmHg, all at 41.11 kg, respectively).

CONCLUSIONS: Buckle design and strap fabric affect the conversion of pulling force to tourniquet strap pressure. Low-friction, smooth, round redirects allow the best conversion.