SEQUESTRATION OF VECURONIUM BROMIDE DURING EXTREMITY SURGERY INVOLVING USE OF A PNEUMATIC TOURNIQUET

Background: We hypothesized that sequestration of a neuromuscular bloc king agent could occur during surgery involving use of an extremity to urniquet and cause changes in neuromuscular function after tourniquet release. Methods: Sixteen patients scheduled for total knee replacemen t were randomized to one of two groups. In Group I, 10 patients were a dministered 0.1 mg/kg of vecuronium 5 minutes prior to inflation of a pneumatic tourniquet; in Group II, 6 patients were administered 0.1 mg /kg of vecuronium after inflation of the tourniquet. The twitch (T-1) and train-of-four (TOF) were analyzed before and after release of the tourniquet, as was the rate of recovery of T-1 and TOF. Serial vecuron ium plasma levels were drawn during the study. Results: The T-1 and TO F responses and the T-1 and TOF recovery rates were not significantly different between groups at tourniquet deflation. In Group I, after re lease of the tourniquet, T-1 and TOF recovery rate decreased significa ntly over a 10-min period (10%+/-3 to 4%+/-4 and 0.12+/-0.06 to 0.06+/ -0.04, mean+/-SD, respectively); in Group II, T-1 and TOF recovery rat e increased significantly over a 10-min period following deflation of the tourniquet (10%+/-6 to 14%+/-7 and 0.10+/-0.03 to 0.18+/-0.02, res pectively). Changes in pharmacodynamics were temporally associated wit h transient but statistically significant changes in vecuronium plasma levels. Overall pharmacokinetics during the study period were compara ble between groups. After administration of neostigmine 30-40 mu g/kg i.v. all subjects in both groups showed complete TOF recovery within 1 5 min. Conclusions: Sequestration of a bolus dose of vecuronium, by a pneumatic tourniquet, causes transient changes in pharmacokinetics and pharmacodynamics. These changes are of limited clinical importance an d do not affect reversibility of neuromuscular block.