We examined the amount of thigh tourniquet pressure that can be reduced from the typical 300 to 350 mm Hg by using a new automated plethysmographic limb occlusion pressure measurement technique. We also examined how much pressure could be reduced by using a wide contoured cuff compared with a standard cuff and if limb occlusion and systolic blood pressures were well correlated. Patients having surgery with a thigh tourniquet were randomized into two groups, one group having surgery with a standard cuff and the other with a wide cuff. Pressure was set at the automatically measured limb occlusion pressure plus a safety margin. Systolic blood pressure and quality of the bloodless field were recorded. The standard cuff maintained an acceptable bloodless field for 18 of 20 patients at an average pressure of 242 mm Hg, and the wide cuff was acceptable for 19 of 20 patients at an average of 202 mm Hg. One patient in each group had a poor bloodless surgical field at the initial pressure, and one patient in each group had a poor bloodless surgical field after a sharp rise in blood pressure during surgery. Systolic blood pressure was not correlated well enough to limb occlusion pressure to be used alone to set the optimum cuff pressure. The automated limb occlusion pressure technique and the wide contoured cuff reduced average pressure by 33-42% from typical pressures.Tourniquets maintain a bloodless surgical field allowing the surgeon to work with greater technical precision in a safe, clear environment. 9 Minimizing tourniquet pressure should reduce the risk of tourniquet-related injuries. 2,9,14,18 However, many surgeons still use a standard pressure based on experience, or they choose a cuff pressure using systolic blood pressure plus a standard margin or multiple. 8,20,23 In a recent survey, surgeons reported that they most commonly used thigh tourniquet pressures of 300-350 mm Hg. 8 These standardized pressures may be substantially higher than necessary for many patients, and insufficient for others. In addition, survey results show that many surgeons still used a standard-width cuff instead of the potentially safer wide contoured cuff, 8 which maintains a bloodless surgical field at a lower cuff pressure. 3,6,7,9,12,13,15,17 Limb occlusion pressure is the tourniquet cuff pressure required to occlude blood flow and accounts for a patient's limb and vessel characteristics and the type and fit of the cuff. Limb occlusion pressure usually is determined by gradually increasing tourniquet pressure until distal arterial pulses cease, as indicated by a Doppler stethoscope, 5,10,11,19 or less commonly by a manually monitored plethysmographic signal. 17 Previous studies have shown that cuff pressure based on limb occlusion pressure measured on each patient before cuff inflation generally is lower than commonly used cuff pressures, but sufficient to maintain a satisfactory operative field. 5,10,17,19 However, based on survey results 8 and our experience, few surgeons use this technique, presumably because existing methods of m...