Cortical evoked potential monitoring during spinal surgery: sensitivity, specificity, reliability, and criteria for alarm.

Cortical somatosensory evoked potentials (EP) were used for intraoperative monitoring of spinal cord integrity during 158 consecutive cases involving surgical correction of spinal deformities. Using a monitoring technique designed to optimize recording, 88% of patients had stable EP results at the time of spinal manipulation. However, five of six patients with preexistent neurological deficits did not have stable EPs. A persistent EP amplitude attenuation of greater than or equal to 40% was a sensitive and specific criterion for alarm. Seven patients had transient attenuations of greater than or equal to 40% after distraction that recovered, so that the distraction instrumentation could be left in place. Overall, this particular cortical somatosensory EP recording technique appears to be appropriate for clinical monitoring. Other recording techniques may be necessary for patients with preexisting neurological deficits.