The influence of hypothermia (surface cooling) on the time-course of action and on the pharmacokinetics of rocuronium in humans.

Hypothermia prolongs the time-course of action of non-depolarizing neuromuscular blocking agents. The mechanism, however, is unknown. We studied the influence of hypothermia (by surface cooling, nasopharyngeal temperature < or = 31 degrees C) on the time-course of action and on the pharmacokinetics of rocuronium in humans. Nineteen neurosurgical patients were divided into hypothermic and normothermic groups. Hypothermia (30.4 +/- 0.8 degrees C (mean +/- SD)) increased the duration of action, temperature dependently, and delayed the recovery. Hypothermia reduced the plasma clearance significantly (2.17 +/- 0.62 vs. 4.26 +/- 0.50 mL kg-1 min-1, P = 0.004), did not change the volume of distribution (224 +/- 64 vs. 232 +/- 60 mL kg-1 min-1, P = 1.0), and prolonged the mean residence time (108 +/- 39 vs. 56 +/- 19 mL kg-1 min-1, P = 0.01). We conclude that hypothermia prolongs the duration of action of rocuronium and delays spontaneous recovery and that altered pharmacokinetics, such as a decreased clearance, play an important role in this.