Surgeon-controlled mivacurium administration during elective Caesarean section

We have compared the dose requirements and recovery characteristics of a continuous mivacurium infusion given by the anaesthetist to maintain 95–100% block at the hand muscles with that of a surgeon-controlled, on-demand dosing technique based on the direct assessment of abdominal muscle tone during elective Caesarean section. Twenty-four full term pregnant patients were included. A rapid-sequence induction using thiopentone 3–5 mg· kg−1 and succinylcholine 1 mg· kg−1 was used. Anaesthesia was maintained with fentanyl, N2O and iso-flurane 0.5%. The mechanomyographic response of the adductor pollicis muscle to supramaximal train-of-four (TOF) ulnar nerve stimulation was recorded. Muscle relaxation was achieved initially with mivacurium 0.1 mg· kg−1 followed either by a continuous infusion of mivacurium to maintain 95–100% block at the adductor pollicis muscle (n = 12) or by surgeon-controlled relaxation (SCR) technique using a syringe pump for patient-controlled analgesia to administer on-demand doses of mivacurium 0.05 mg · kg−1 (n = 12). The lockout interval was three minutes and the maximum hourly dose of mivacurium allowed was 0.6 mg · kg−1. The total doses of mivacurium (mean ±SD) were 23.2 ± 10.4 and 12.4 ± 3.5 mg in the infusion and SCR groups, P < 0.01. On-demand, surgeon-controlled doses of mivacurium were injected at a mean of T1 42.3 ± 36%. At the end of surgery, T1 and TOF ratio were respectively 16.7 ± 13%, 5 ± 10% and 48 ± 37%, 30 ± 24% in the infusion and SCR groups. Five patients in the SCR group and one patient in the infusion group did not receive antagonist at the end of surgery. The time to adequate recovery, TOF 75%, after skin closure was 8.2 ± 2.3 and 5.3 ± 4 min in the infusion and SCR groups, P = 0.05. It is concluded that, compared with a continuous mivacurium infusion, the SCR technique is associated with reduced mivacurium requirements, a substantial degree of neuromuscular recovery at the end of surgery and a reduced need for neostigmine reversal in full term pregnant patients undergoing elective Caesarean section.