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.