Intraoperative hypoxia detected by evoked potential monitoring.

Somatosensory cortical evoked potentials (SCEP) are used to monitor spinal cord function during operations on the spine and spinal cord (1-3). These intermediate latency responses to stimulation of peripheral nerves originate in the cerebral cortex (4). They are subject to alteration by anesthetics (5,6) and by perturbations of physiologic state that may occur during surgery (7, 8). If SCEP monitoring is to reflect reliably surgical trespass on sensory pathways, potentially confounding factors that also affect SCEP must be monitored and kept as constant as possible. SCEP recording may detect not only physical encroachment on conducting pathways at the operative site but also systemic physiologic changes that require correction. We have observed SCEP alterations as the presenting manifestation of intraoperative hypoxia.