Sequestration of vecuronium bromide during extremity surgery involving use of a pneumatic tourniquet.

Background: We hypothesized that sequestration of a neuromuscular blocking agent could occur during surgery involving use of an extremity tourniquet and cause changes in neuromuscular function after tourniquet release.
Methods: Sixteen patients scheduled for total knee replacement were randomized to one of two groups. In Group I, 10 patients were administered 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 (T1) and train-of-four (TOF) were analyzed before and after release of the tourniquet, as was the rate of recovery of T1 and TOF. Serial vecuronium plasma levels were drawn during the study.
Results: The T1 and TOF responses and the T1 and TOF recovery rates were not significantly different between groups at tourniquet deflation. In Group I, after release of the tourniquet, T1 and TOF recovery rate decreased significantly 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, T1 and TOF recovery rate 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, respectively). Changes in pharmacodynamics were temporally associated with transient but statistically significant changes in vecuronium plasma levels. Overall pharmacokinetics during the study period were comparable between groups. After administration of neostigmine 30-40 micrograms/kg i.v. all subjects in both groups showed complete TOF recovery within 15 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 and do not affect reversibility of neuromuscular block.