Background and objective: Monitoring of neuromuscular blockade still often relies on clinical judgement. Moreover, there are substantial national differences in the use of agents to 'reverse' their effects. We investigated the recovery characteristics and incidence of postoperative residual curarization after cisatracurium and rocuronium infusions for long duration interventions without systematic antagonism.

Methods: In 30 patients undergoing major surgery, we measured infusion dose requirements for rocuronium and cisatracurium during propofol anaesthesia. Infusions were discontinued at the beginning of surgical closure; spontaneous recovery of neuromuscular function was awaited in both groups. Neostigmine (50 μg kg−1) was administered only when a patient started to wake without a train-of-four ratio (TOF) of 0.9.

Results: In the cisatracurium and rocuronium groups, four (27%) and one (7%) patients, respectively, had a TOF ratio ≥0.9 at the end of surgery. The TOF ratio in each group at that time was 51 ± 32% for cisatracurium and 47 ± 31% for rocuronium (P = 0.78). Six patients (40%) in the cisatracurium group and seven (47%) in the rocuronium group required neostigmine. The TOF ratio at the time of reversal was 63 ± 7% for cisatracurium and 40 ± 19% for rocuronium (P = 0.01). The time interval between the end of surgery and a TOF ratio of 0.9 was 10 ± 9 min for cisatracurium and 18 ± 13 min for rocuronium (P = n.s.).

Conclusions: Patients receiving a cisatracurium or rocuronium infusion have a high incidence of postoperative residual curarization when the block is not antagonized. When ‘reversal’ is not attempted, cisatracurium seems to be safer than rocuronium.