MONITORING OF INTRAOPERATIVE MOTOR-EVOKED POTENTIALS UNDER CONDITIONSOF CONTROLLED NEUROMUSCULAR BLOCKADE

Motor-evoked potentials were recorded after electrical spinal cord sti mulation in 19 patients undergoing neurosurgical or orthopedic procedu res. Anesthesia was maintained with nitrous oxide, opioids, and inhale d anesthetics. Vecuronium was infused sufficient to eliminate 90% of t witch tension. The spinal cord was stimulated using either epidural or subarachnoid electrodes. Compound muscle action potentials were recor ded from quadriceps and tibialis anterior muscles. Well-formed, stable motor-evoked potentials were recorded in all but one patient, in whom a preexisting myelopathy was felt to preclude recording. Intraoperati ve deterioration of motor-evoked potentials occurred in one patient wh o had a postoperative neurologic deficit. This study demonstrates the feasibility and utility of intraoperative motor tract monitoring using direct spinal cord stimulation. Controlled neuromuscular blockade per mits recording of compound muscle action potentials while eliminating patient motor activity that could interfere with surgery.