Effect of nitrous oxide on visual, auditory and somatosensory evoked potentials

The effects of 10%, 30% and 50% nitrous oxide on visual, auditory and somatosensory evoked potentials were studied in seven healthy volunteers. The evoked potentials were averaged from the electroencephalogram following repeated peripheral sensory stimulation of the appropriate modality. Latencies and amplitudes of the resulting potentials were measured and compared with control values. In five subjects, increasing concentrations of nitrous oxide were associated with a graded reduction in amplitude of the visual (P less than 0.02) and somatosensory (P less than 0.02) evoked potentials. The latency of the first major negative potential of the visual evoked potential was significantly increased (P less than 0.02). Latencies of brainstem auditory evoked potentials did not alter. In the other two subjects the amplitudes of the visual and somatosensory evoked potentials showed graded increase with decreasing concentrations of nitrous oxide, confirming that the changes are dose related. As nitrous oxide is used almost universally during anaesthesia, these changes must be taken into account when assessing variations observed during operation in anaesthetic-related evoked potential studies.