Metocurine kinetics in patients undergoing operations requiring cardiopulmonary bypass

Metocurine kinetics were determined in 10 patients undergoing operations requiring hypothermic cardiopulmonary bypass (CPB) and nine patients of similar age undergoing operations of similar duration but not requiring CPB. The metocurine dosage regimen was a bolus of 0.3 mg/kg given concomitantly with the commencement of an infusion at a rate of 0.04 mg/kg/hr; this regimen was designed to produce and maintain a plasma metocurine concentration associated with 95% depression of the twitch response. Metocurine kinetics were affected minimally by hypothermic CPB. The kinetic parameters including volumes of distribution at steady state of 0.35 L/kg and 0.34 L/kg and elimination clearances of 1.3 ml/min/kg and 1.1 ml/min/kg in the control and CPB groups, respectively, are in agreement with the results of others. Changes in neuromuscular blockade with the onset of CPB and the return to original blockade intensities with rewarming suggest a decreased sensitivity to the effects of metocurine at lower temperatures.