EFFECTS OF HYPOTHERMIC CARDIOPULMONARY BYPASS ON THE PHARMACODYNAMICSAND PHARMACOKINETICS OF ROCURONIUM

Objective: To study the influence of hypothermic cardiopulmonary bypas s (CPB) on the pharmacodynamics and pharmacokinetics of rocuronium. De sign: Prospective, descriptive study. Setting: Operating room at a uni versity hospital. Participants: Ten ASA class III end IV patients, ran ging in age from 35 to 75 years, scheduled for elective coronary arter y bypass grafting. Interventions: Neuromuscular transmission was monit ored mechanomyographically. The time course of action of maintenance d oses and plasma concentration-response relationships were determined b efore, during, and after OPE. The plasma concentration decay and renal elimination were studied simultaneously. Plasma and urine concentrati on of rocuronium ware determined by high-performance liquid chromatogr aphy. Measurements and Main Results: Hypothermic CPB prolonged the dur ation of action of coincided with a lower plasma concentration at a tw itch response of 5% of control. The duration of action of maintenance doses returned to prehypothermic CPB level after rewarming to a nasoph aryngeal temperature of 37 degrees C. The plasma concentration-respons e relationship did not return to precooling control value, probably ow ing to persisting peripheral hypothermia. Both the renal elimination o f rocuronium and the plasma concentration decay after the last mainten ance dose under normothermic conditions resembled values obtained in p atients not undergoing hypothermic CPB. Conclusions: Hypothermic CPB p rolongs the duration of action of maintenance doses and alters the pla sma concentration-response relationship of rocuronium. These changes m ay be the result of, on the one hand, an increased sensitivity of the neuromuscular transmission and/or decreased muscle contractility and, on the other hand, the result of a reduced plasma clearance during hyp othermia. (C) 1995 by W.B. Saunders Company