INTRAOPERATIVE MONITORING OF MOTOR EVOKED-POTENTIALS - A REVIEW OF 116 CASES

We reviewed the results of motor evoked potential (MEP) and somatosens ory evoked potential (SEP) monitoring during 116 operations on the spi ne or spinal cord. We monitored MEPs by electrically stimulating the s pinal cord and recording compound muscle action potentials from lower extremity muscles and monitored SEPs by stimulating posterior tibial o r peroneal nerves and recording both cortical and subcortical evoked p otentials. We maintained anesthesia with an N2O/O-2/opioid technique s upplemented with a halogenated inhalational agent and maintained parti al neuromuscular blockade using a vecuronium infusion. Both MEPs and S EPs could be recorded in 99 cases (85%). Neither MEPs nor SEPs were re corded in eight patients, all of whom had preexisting severe myelopath ies. Only SEPs could be recorded in two patients, and only MEPs were o btained in seven cases. Deterioration of evoked potentials occurred du ring nine operations (8%). In eight cases, both SEPs and MEPs deterior ated; in one case, only MEPs deteriorated. In four cases, the changes in the monitored signals led to major alterations in the surgery. We b elieve that optimal monitoring during spinal surgery requires recordin g both SEPs and MEPs. This provides independent verification of spinal cord integrity using two parallel but independent systems, and also a llows detection of the occasional insults that selectively affect eith er motor or sensory systems.