Effect of fentanyl and naloxone on the P300 auditory potential

The effect of fentanyl (opioid agonist) and naloxone (morphine antagonist) on the amplitude, area and latency of the P300 auditory potential was studied in patients undergoing minor surgical procedures. Fentanyl (5.0 micrograms/kg), naloxone (3.0 micrograms/kg) and isotonic saline (for control) were injected intravenously through a catheter just before surgery, and following a single-blind procedure and three different pharmacological paradigms with three consecutive conditions each: (1) initial baseline (C), saline (S) and late baseline (C'); (2) C, fentanyl (F) and C'; (3) C, naloxone (N) and C'. Fentanyl significantly reduced the amplitude and area with no changes in the latency of small (S) and large (L) P300 potentials. Concomitantly, fentanyl increased the number of omitted counts of the target tones of the "odd ball" P300 test and the spatial threshold of the two point discrimination test in patients with small and large P300 potentials. Naloxone significantly increased the amplitude and area and decreased the latency of the small P300 potential and decreased the amplitude and area with no changes in latency of the large P300 potentials. Concomitantly, naloxone decreased the number of omitted counts of the patients with small but not large P300 potentials and decreased the spatial threshold in patients with both small and large P300 potentials. Neither fentanyl nor naloxone produced systematic changes in the evaluation of pain and hearing of patients with small and large P300 potentials. Although dramatic changes in pulse, blood pressure, respiration and EEG were found in some cases immediately after the administration of fentanyl and naloxone, these changes were not consistent and were not present at the time other tests were performed.