Somatosensory evoked potential monitoring during Cotrel-Dubousset instrumentation. Report of a case.

Somatosensory evoked potentials produced by electrical stimulation of the posterior tibial nerve were recorded from surface electrodes at the scalp and cervical spine of a patient with scoliosis undergoing posterior spinal fusion with Cotrel-Dubousset instrumentation. During spinal derotation when hypotension and anemia were also present, the cortical and subcortical somatosensory evoked potentials disappeared. During a wake-up test, the patient demonstrated weakness of the left lower extremity, and derotation was stopped. The patient was given pharmacologic hypertensive agents and blood transfusions to increase blood pressure. Forty minutes later, somatosensory evoked potentials returned and a second wake-up test demonstrated normal function in both lower extremities. This report demonstrates the accuracy and usefulness of somatosensory evoked potential monitoring during spinal fusion with Cotrel-Dubousset instrumentation. To the authors knowledge, this is the first report demonstrating a correlation between abnormal SEP responses and intraoperative neurologic deficit during the derotation maneuver with Cotrel-Dubousset instrumentation and corrected by transfusion and restoration of normotension.