Event-related potential correlates of analgesia; comparison of fentanyl, acupuncture, and nitrous oxide.

This study was undertaken to determine whether different analgesic treatments result in a common change in the event-related potentials (ERP) elicited during painful dental stimulation. The effects of electrical acupuncture delivered at 2 Hz to LI-4, the opiate fentanyl 0.1 mg i.v., and the inhalation analgesia mixture of 33% nitrous oxide in oxygen were examined in volunteers undergoing painful tooth pulp stimulation. ERPs were recorded at vertex and subjects provided reports of pain intensity. Discriminant function analysis was used to determine which subset of the pain report and ERP variables could best discriminate baseline from treatment conditions without regard to specificity of treatment. Together with pain report, amplitude of the ERP positive deflection at 250 msec was a significant indicator of analgesia across the 3 treatments. Other changes specific to the individual treatments were also observed. Since the 250 msec amplitude measure was not redundant statistically with pain report, the ERP data provided significant new information about analgesia even though pain report was a very sensitive measure. Pain report alone could account for 48% of the variance across treatments while ERP measures alone accounted for 34%.