Brain stem and somatosensory evoked potentials: application in the operating room and intensive care unit

Intraoperative monitoring of the brain's electrical function with evoked potentials (EPs) may prove as valuable as cardiac monitoring in detecting abnormalities before permanent damage occurs. To date, evoked potential monitoring has only been employed in select neurological cases, where the significance of electrical changes can be related to postoperative deficits. If EP intraoperative techniques are to be useful in preventing these postoperative deficits, they must be able to predict impending brain dysfunction during surgery. There is strong clinical and experimental data relating EP changes to critical blood flow, brain retraction, and CNS manipulation. However, little is known of the normal fluctuations in electrical activity during routine non-neurological surgery. The data we have collected in control patients (non-neurological) will be a guide to the interpretation of neurological cases (carotid endarterectomy, aneurysm, and cervical spine and cord lesions). We have concentrated on monitoring somatosensory and auditory short-latency EPs since they appear to be the most stable, reproducible and the most applicable to patient monitoring during neurosurgical, vascular and orthopedic procedures.