SURGEON-CONTROLLED MIVACURIUM ADMINISTRATION DURING ELECTIVE CESAREAN-SECTION

We have compared the dose requirements and recovery characteristics of a continuous mivacurium infusion given by the anaesthetist to maintai n 95-100% block at the hand muscles with that of a surgeon-controlled, on-demand dosing technique based on the direct assessment of abdomina l muscle tone during elective Caesarean section. Twenty-four full term pregnant patients were included. A rapid-sequence induction using thi opentone 3-5 mg . kg(-1) and succinylcholine 1 mg . kg(-1) was used An aesthesia was maintained with fentanyl, N2O and isoflurane 0.5%. The m echanomyographic response of the adductor pollicis muscle to supramaxi mal train-of-four (TOF) ulnar nerve stimulation was recorded. Muscle r elaxation was achieved initially with mivacurium 0.1 mg . kg(-1) follo wed either by a continuous infusion of mivacurium to maintain 95-100% block at the adductor pollicis muscle (n = 12) or by surgeon-controlle d relaxation (SCR) technique using a syringe pump for patient-controll ed analgesia to administer on-demand doses of mivacurium 0.05 mg kg(-1 ) (n = 12). The lockout interval was three minutes and the maximum hou rly dose of mivacurium allowed was 0.06 mg . kg(-1). The total doses o f mivacurium (mean +/- SD) were 23.2 +/- 10.4 and 12.4 +/- 3.5 mg in t he infusion and SCR groups, P < 0.01. On-demand, surgeon-controlled do ses of mivacurium were injected at a mean of T-1 42.3 +/- 36%. At the end of surgery, T-1 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 no t receive antagonist at the end of surgery. The time to adequate recov ery, TOF 75%, after skin closure was 8.2 +/- 5.3 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 neuromus cular recovery al the end of surgery and a reduced need for neostigmin e reversal in full term pregnant patients undergoing elective Caesarea n section.