Middle latency auditory evoked potentials during total intravenous anesthesia with droperidol, ketamine and fentanyl.

We investigated whether total intravenous anesthesia with ketamine, fentanyl and droperidol would affect middle latency auditory evoked potentials and explicit memory, and whether dreams during the anesthesia are related to plasma concentrations of fentanyl and the infusion technique. A total number of 40 patients were the subjects for this study. Twenty patients (group A) were maintained with intravenous ketamine 2 mg kg-1 hr-1 and fentanyl 5 micrograms kg-1 hr-1 for the first 60 min and 3 micrograms kg-1 hr-1 for the next 90 min, and droperidol 0.1 mg kg-1. The remaining 20 patients (group B) were maintained with intravenous ketamine 2 mg kg-1 hr-1, droperidol 0.1 mg kg-1 and fentanyl 50-100 micrograms in a bolus intermittently as needed by vital signs such as increases in heart rate and arterial blood pressure. Middle latency auditory evoked potentials, plasma fentanyl and ketamine levels were measured; explicit memory and dreams were also estimated. There were no patients who recollected explicit memories of intraoperative events in both groups. The middle latency auditory evoked potentials were not significantly changed during the anesthesia in both groups. We could find no significant differences in latencies and amplitudes of the middle latency auditory evoked potentials between the both groups. Plasma fentanyl levels of group B patients were significantly lower than those of group A patients and the incidence of the dreams was significantly higher in group B patients. We conclude that the anesthesia with ketamine, fentanyl and droperidol is not associated with the explicit memories, though the middle latency auditory evoked potentials were not significantly changed as compared with those in the waking state. In addition, dreams during the anesthesia may correlate with plasma fentanyl concentrations or the infusion technique.