Quantitative evaluation of tourniquet leak during i.v. regional anaesthesia of the upper and lower limbs in human volunteers.

Although it is accepted that during i.v. regional anaesthesia (IVRA) local anaesthetic can leak under the tourniquet into the systemic circulation, no published study has evaluated this leak quantitatively. In volunteers, during two random sessions, we have simulated IVRA using standard techniques with a radiolabelled compound which is chemically similar to lignocaine and has comparable tissue distribution (0.1 mg of HIDA labelled with 100 muCi of 99mTc in 40 ml of saline). The decrease in radioactivity was measured with a gamma camera for the 20 min of tourniquet inflation and for the 20 min of washout after cuff deflation. While the tourniquet was inflated, the leak for the lower limb (mean 29 (SD 8) %) was significantly greater (P < 0.004) than the leak for the upper limb (15 (5) %). Moreover, in each of 10 volunteers, the leak was always greater for the lower than the upper limb. During the first 3 min after tourniquet deflation the loss of radioactivity was 58 (8) % of the maximal amount for the upper limb and 39 (8) % for the lower limb (P < 0.001). As the leak under the tourniquet was significantly greater for the lower than the upper limb, we conclude that IVRA for the lower limb can be associated more frequently with a shorter duration of successful anaesthesia and/or failure.