Fentanyl plasma concentrations maintained by a simple infusion scheme in patients undergoing cardiac surgery

The ability of a simple infusion scheme for fentanyl to achieve and maintain one of two target concentrations of fentanyl in plasma was studied in 17 patients having cardiac surgery that required the use of moderate hypothermic cardiopulmonary bypass (CPB). All patients received preanesthetic medication including morphine, a benzodiazepine, and/or scopolamine. Anesthesia was induced and maintained by one of two fentanyl infusion regimens: HIGH-FEN (n = 6), a priming infusion of 2.4 μg · kg^-1 · min^{- 1} for 20 min in combination with a continuous infusion of 0.3 μg · kg^-1 · min^-1 for the duration of the operation to produce a plasma fentanyl concentration of 20-25 ng/mL; or LOW-FEN (n = 11), priming and maintenance infusions of 2.4 and 0.15 μg · kg^-1 · min^-1 designed to produce a fentanyl concentration of 12-15 ng/mL of plasma. The six patients receiving HIGH-FEN had plasma fentanyl concentrations maintained between 20 and 27 ng/mL and none required anesthetic supplementation before CPB; one patient required a single dose of thiopental 50 mg after the termination of CPB. The total fentanyl dose for the operation (3.2 ± 0.1 h) averaged 107 ± 2 μg/kg (range 100.5-115.5 μg/kg). The 11 patients receiving LOW-FEN had a plasma fentanyl concentration maintained below 20 ng/mL (range 13-17 ng/mL). Eight patients before and 10 patients after CPB required anesthetic supplementation for adverse hemodynamic or somatic responses. For comparison purposes, another eight patients received a single 75 μg/kg dose of fentanyl during 20 min for induction of anesthesia, and 7 of the 8 required supplemental anesthetic agents before and after CPB. We conclude that target fentanyl concentrations in plasma can be maintained throughout the operation by using a simple infusion scheme despite the potential alterations in drug disposition that occur during and after CPB. After appropriate premedication, plasma fentanyl concentrations between 20 and 27 ng/mL were associated with very few hemodynamic and somatic responses indicative of inadequate anesthesia. With the HIGH-FEN infusion scheme, patients were ready for tracheal extubation the morning after surgery.