Background: This study was performed to investigate residual neuromuscular block levels of rocuronium, the new, nondepolarizing muscle relaxant with intermadiate duration, in the variable hypothermic cardiopulmonary bypass conditions.

Methods: After ethic committee’s approval, 30 patients scheduled for an elective coronary artery bypass operation were randomised into two groups: Group I with mild hypothermia (30-35°C), and Group II with moderate hypothermia (25-30°C). After premedication with diazepam, anaesthesia was induced with diazepam, fentanyl and rocuronium. Patients’ neuromuscular monitoring was eveluated with TOF (train of four)-Guard instruments. Endotracheal entubation was performed when the Twitch (Tw) height was 0%. After induction; when the Tw height reached 10%, muscle relaxation was maintained with infusion of rocuronium (0.6 mg/kg/h). The dose was adjusted to keep Tw response as 10%. The dosage of rocuronium was reduced in hypothermic periods. Infusion of rocuronium was stopped when the sternum was closed. In the postoperative period, time follow up was recorded when Tw height became 25% till the TOF ratio reached (T4/T1) > 0.7. When this time was over 30 minutes, that was assessed as residual neuromusculer block.

Results: Group II had significantly higher spontaneus recovery times and residual neuromuscular block percentage than Group I.

Conclusion: In patients undergoing coronary artery bypass with prolonged hypothermia under 30°C, spontaneus recovery times and postoperative residual neuromuscular block increase significantly, and the need for muscle relaxant decreases by deepening the hypothermia.

Keywords : Rocuronium, hypothermia, residual neuromuscular block