ABSTRACT
Intraoperative evoked potential monitoring is most commonly used for surgery involving cranial nerves or the spinal cord. Brainstem auditory evoked potentials (BAEPs) and direct recordings from the eighth nerve are used during cranial nerve surgery to monitor eighth nerve function. 5,6 Significant changes in the latency of peaks in the response can occur over 1 min or less. These changes are probably due to stretching of the eighth nerve or pressure on the nerve due to retraction. Electromyographic signals in response to electrical or mechanical stimulation of the facial nerve have been used to monitor facial nerve function. 7,8
Somatosensory evoked potentials (SSEPs), recorded on the head in response to stimulation of the tibial or peroneal nerve in the leg, and direct stimulation and recording from the exposed spinal cord have been used to monitor spinal cord function. 9 Significant increases in peak latency and/or decreases in peak amplitude can occur over a few minutes. These changes may be due to interruption of blood flow to the spinal cord or to stretching of or pressure on the cord due to retraction. Recently, interest has developed in monitoring motor pathway function by stimulating the motor cortex or spinal cord and recording a peripheral nerve response or electromyographic signal from muscle;
Jacobson and Tew review this area and note that use of these techniques for monitoring is still in development.4
