Conducted somatosensory evoked potentials during spinal surgery. Part 1: control conduction velocity measurements

Intraoperative recordings of conducted bipolar epidural somatosensory evoked potentials (SEP's) generated by unilateral common peroneal nerve stimulation have been obtained in 27 patients. The SEP's were multiphasic, 0.3 to 1.5 microV in amplitude, and recorded in 100% of patients with normal cords or in patients with spinal lesions, at a site caudal to the lesions. Control spinal conduction velocities (CV's), measured in the midthoracic to lower cervical regions, were in the range of 65 to 85 m/sec. Control lumbar and lower thoracic CV's were in the range of 30 to 45 m/sec. The CV values were obtained periodically throughout the course of surgery and were plotted as a function of time. In control patients with extradural lesions and neuroleptic anesthesia, the CV's remained constant (+/- 3%). The consistency, sensitivity, and safety of SEP recordings obtained by this technique make precise monitoring readily available during spinal operations.