Absence of seizures during induction of anesthesia with high-dose fentanyl

Anesthesia was induced in six patients scheduled for elective aortocoronary bypass (ACB) surgery with intravenous fentanyl, either 50 (n = 2) or 150 micrograms/kg (n = 4) over 20 or 60 sec, respectively. Patients had been given their usual antianginal medications before surgery and were premedicated with morphine sulfate. Arterial plasma fentanyl levels were measured repetitively at frequent intervals, and eight leads of the cortical electroencephalogram (EEG) were recorded continuously. Peak plasma fentanyl concentrations exceeded 1750 ng/ml at the end of the injection of 150 micrograms/kg and then decreased by more than 75% within 3 min. In an additional two patients, incremental doses of fentanyl (25, 25, 50, 50 micrograms/kg; total 150 micrograms/Kg) maintained fentanyl concentrations between 30 and 650 ng/ml for the entire 15 min of the study. In all cases, diffuse slow-wave EEG activity, characteristic of fentanyl anesthesia, was seen. Motor activity, including wrist flexion and ocular movements, was observed during the onset of fentanyl-induced truncal rigidity, but no seizure-like activity was found in the EEG.