Intraoperative somatosensory potential monitoring.  A clinical analysis of 127 surgical procedures. 
During 127 operations for the correction of spinal deformities the spinal cord function was controlled by intraoperative monitoring.  Cortical somatosensory evoked potentials (CSEP) were obtained by bilateral stimulation of the posterior tibial nerves at the ankle and recorded from electrodes at Fz-Cz.  In addition, unilateral median nerve stimulation at the wrist was carried out to act as a control.  Six cases with significant intraoperative alterations in wave-form and their postoperative neurologic status are described in detail.  EP monitoring permits continuous monitoring of the patient for the total duration of operation and is therefore superior to the wake-up test.  This method is particularly advisable for operations carried out in hypotensive anaesthesia as well as for postoperative control.