Effects of Nitrous Oxide, Transcutaneous Electrical Stimulation, and Their Combination on Brain Potentials Elicited by Painful Stimulation

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Abstract
Combinations of transcutaneous electrical stimulation (TES) and inhalation of N2O with O2 were used for surgical pain control and the possible synergism of these 2 were explored. During painful dental stimulation, 18 subjects gave pain reports while event-related potentials were recorded at vertex. Electrical stimulation was delivered bilaterally at the LI-4 acupuncture points on the hands at 20 Hz, mean = 9.65 mA intensity. Inhalation treatment was N2O 33% with O2. Testing was done on 2 days to permit evaluation of each treatment alone and their combination. Treatment sequence was counterbalanced. Base-to-peak amplitude and peak latency scores were derived for the event-related potentials under each testing condition. Both stimulation and inhalation treatments altered event-related potential scores and pain report. The combination treatment was significantly more effective than stimulation alone but was not significantly more effective than N2O alone. N2O with O2 alone reduced peak amplitude at 250 ms and 350 ms, as well as pain report. It increased peak latency at 100 ms. Transcutaneous electrical stimulation alone decreased peak amplitude and latency at 150ms and increased peak latency at 350 ms. Decreased peak amplitude at 250 ms and increased peak latency at 150 ms were observed when inhalation was added to stimulation, and there was a significant reduction in pain report. Nine control subjects were studied to demonstrate that analgesic changes were not due to repeated testing. These outcomes demonstrated no synergism between the stimulation and inhalation treatments. N2O apparently blocks the effects of electrical stimulation at LI-4.