Depression of cortical somatosensory evoked potentials by nitrous oxide.

The effects of the inhalation of 50% nitrous oxide on somatosensory evoked potentials during a fentanyl-oxygen anaesthetic technique for central nervous system surgery were evaluated. The latency and amplitude of the first cortical wave were obtained using conventional somatosensory techniques with median or posterior tibial nerve stimulation. Data were collected before and after the inhalation of 50% nitrous oxide in oxygen introduced at the conclusion of the surgical procedure. The addition of nitrous oxide was associated with consistent decreases in the amplitude of somatosensory evoked potentials, but with no significant changes in latency. Since no electrical, physiological, or surgical event was associated with these changes, the results suggest that they were attributable to nitrous oxide per se.