Mivacurium is mainly metabolized by plasma cholinesterase, whereas atracurium is removed by Hofman elimination. The purpose of this study was to compare the infusion rate of atracurium and mivacurium in maintaining surgical relaxation, and to compare their recovery indices between parturients and non-pregnant women. Muscle relaxation was maintained by the continuous infusion of relaxants to retain the first response of train-of-four (TOF) at 5% of control. When mivacurium was used, Bolus-T5 (duration from the end of mivacurium bolus injection to 5% single twitch recovery) was measured. After discontinuing the infusion, the recovery index was measured. The infusion rate of mivacurium, not atracurium, was significantly lower in parturients and Bolus-T5 of parturients was significantly longer than that of non-pregnant women. There was no significant difference in the recovery indices of both relaxants. The authors concluded that the infusion rate of mivacurium in maintaining muscle relaxation in parturients should be reduced compared to the rate in non-pregnant women and measuring Bolus-T5 may be helpful in determining the infusion rate to maintain muscle relaxation.
Adult ; Atracurium/therapeutic use ; Atracurium/administration & dosage* ; Cesarean Section* ; Comparative Study ; Female ; Human ; Injections, Intramuscular ; Isoquinolines/therapeutic use ; Isoquinolines/administration & dosage* ; Neuromuscular Nondepolarizing Agents/therapeutic use ; Neuromuscular Nondepolarizing Agents/administration & dosage* ; Pregnancy

OBJECTIVETo study the effect of the degree of muscle relaxation on motor-evoked potential elicited by transcranial electrical stimulation in patients undergoing spine surgery.

METHODSSixty ASA I or II patients undergoing spine surgery were randomly divided into 5 groups (n=12). After an initial intubation, continuous cisatracurium infusion was administered with continuous monitoring of T1. The infusion dose was adjusted according muscle relaxation monitoring, and different muscle relaxation degrees were maintained in the 5 groups. The band and latency of D1 in motor-evoked potential was observed with also subjective assessment of the muscle relaxation.

RESULTSSignificant differences in the band and latency were noted in groups I and II compared with the reference values, but not in groups III, IV and V. Subjective assessment revealed significant differences between groups IV and V and groups I and III in terms of the number of cases with poor muscle relaxation.

CONCLUSIONT1 value between 10% and 15% is sufficient for MEP monitoring and allows the maintenance of good muscle relaxation during spine surgery.

Atracurium ; therapeutic use ; Electric Stimulation ; Evoked Potentials, Motor ; Humans ; Monitoring, Intraoperative ; Muscle Relaxation ; Neuromuscular Nondepolarizing Agents ; therapeutic use ; Orthopedic Procedures ; methods ; Spine ; surgery