MYOGENIC MOTOR-EVOKED POTENTIAL MONITORING USING PARTIAL NEUROMUSCULAR BLOCKADE IN SURGERY OF THE SPINE

Study Design. The authors analyzed motor-evoked potentials using trans cranial electrical cortical stimulation during spinal surgery in 40 pa tients under conditions of partial neuromuscular blockade. Objectives. The results were used to investigate the utility of motor-evoked pote ntial monitoring to prevent neurologic injury in spinal surgery. Summa ry of Background Data. Noninvasive transcranial electrical motor-evoke d potentials are reportedly effective in predicting postoperative spin al cord deficits caused by intraoperative occurrences. However, the se nsitivity and specificity of these predictions have not been assessed under conditions of partial neuromuscular blockade during a wide varie ty of surgical procedures. Methods. Compound muscle action potentials were recorded at the tibialis anterior muscle while general anesthesia was maintained with nitrous oxide, etomidate, and sufentanil. Surgery was performed at all spinal levels for a variety of diagnoses. Result s. Reference motor-evoked potential amplitudes, measured after inducti on of partial neuromuscular blockade, ranged from 25 to 7562 mu V (med ian, 600 mu V). Variation in intraoperative motor-evoked potential amp litude ranged from signal loss to a 3440% increase. A decrease to less than 20% of the individual reference value for motor-evoked potential amplitude occurred at least once in nine patients (22.5%) but was not associated with postoperative motor deficits. Two patients who had lo ss of motor-evoked potential signal without recovery did have postoper ative motor deficits. Motor-evoked potentials predicted postoperative motor improvement in six patients. An improvement threshold of 160% of the reference amplitude predicted postoperative motor improvement wit h 100% sensitivity and 81% specificity. Conclusions. The authors suppo rt the utility of recording transcranial electrical motor-evoked poten tials in spinal surgery under partial neuromuscular blockade. Recovery of lost motor-evoked potentials was not associated with postoperative motor deficits, whereas non-recovery of lost motor-evoked potentials was.