Intubating conditions and neuromuscular block after divided dose mivacurium or single dose rocuronium

To evaluate the tracheal intubating conditions and neuromuscular blocking characteristics of divided dose mivacurium or single dose rocuronium.

Thirty-two patients undergoing elective surgery were studied. Anaesthesia was with propofol 2 mg.kg-1, followed by an infusion of 150 micrograms.kg-1.min.1. Patients were randomized to receive either mivacurium-0.15 mg.kg-1 followed 30 sec later by 0.1 mg.kg-1, or rocuronium- 0.9 mg.kg-1, followed 30 sec later by placebo. Tracheal intubating conditions were assessed 90 sec after the initial dose of relaxant by an anaesthetists who was unaware of patient group. The electromyographic (EMG) response of the first dorsal interosseus muscle to ulnar nerve train-of-four was measured.

Successful tracheal intubation was performed in all patients after both mivacurium and rocuronium. Intubating conditions (jaw relaxation, open visible vocal cords) were judged to be good-excellent in all but one patient before insertion of the tracheal tube. However, patients receiving mivacurium were more likely to experience coughing and bucking after tracheal tube insertion (10/16 patients) than those receiving rocuronium (3/16 patients, P < 0.05). No patient in the rocuronium group experienced moderately vigorous coughing and bucking after insertion of the tracheal tube vs six patients in the mivacurium group (P < 0.05). Time to 10 and 25% recovery of neuromuscular function was faster (P < 0.05) after divided dose mivacurium (20 +/- 1 and 23 +/- 1 min, respectively) than after rocuronium (45 +/- 5 and 57 +/- 8 min, respectively).

The results suggest that, during conditions of the study, divided dose mivacurium is not recommended for a 90-sec tracheal intubation in patients where moderate coughing and bucking is deemed unacceptable.