Two Mathematical Methods to Estimate Arterial Occlusion Pressure and Tourniquet Effectiveness in Lower Limb Surgery

Pneumatic tourniquets are widely used not only to reduce blood loss and to ensure optimal operating conditions during extremity surgery, but also in regional anesthesia (local intravenous) vein puncture and to control life or limb threatening conditions. However, compression of the tissues under a tourniquet is associated with soft tissue damage involving the skin, vessels, muscles, and most importantly, nerves, and are commonly pressure related and can be affected by tourniquet time as well. Therefore, the "minimal tourniquet inflation pressure" necessary to provide a bloodless field has been suggested to minimize the risk of complications from excessive inflation pressure. Arterial occlusion pressure (AOP) is the lowest pneumatic tourniquet inflation pressure required to stop the arterial blood flow into the limb, and its usage has been shown to be useful in optimizing tourniquet cuff pressures. The pressure to which a pneumatic tourniquet cuff should be inflated depends on a number of variables, including the patient's age, skin, blood pressure and the shape and size of the extremity in question, as well as the dimensions of the cuff. One of the estimation method for AOP is based on systolic blood pressure (SBP) and tissue padding coefficient (KTP) values (AOP=\[SBP+10\]/KTP) according to extremity circumferences. Unver B. et al., used this method to estimate effective tourniquet pressure in total knee replacement under hypotensive general anesthesia tourniquet pressure achieved was 169.7±7.9 mmHg, while Tuncali et al., tested it again in different lower limb surgeries under general or neuraxial anesthesia with normotensive techniques and the achieved maximal tourniquet pressures used was 173.3±15.6 mmHg. Hong-yun Liu et al., established a new occlusion pressure mathematical model for the upper limb based on the correlation analysis between several possible influencing parameters and the minimal pneumatic tourniquet pressure.