Induction Using Fentanyl to Suppress the Intubation Response in the Cardiac Patient: What is the Optimal Dose?

Abstract

Eighty patients undergoing coronary artery surgery were randomly allocated to receive either 0, 2, 5, 10 or 15 jig/kg of fentanyl with induction of anaesthesia. Heart rate and blood pressure were measured before induction, after induction, and after intubation. The effects of fentanyl dose on both heart rate and mean arterial pressure (MAP) were evaluated in terms of both the mean and group responses. At all doses of fentanyl, mean heart rate increased after induction and rose further on intubation. The mean increase after induction was minimal at doses of 5 μg/kg and greater. The increase in heart rate after intubation was more difficult to block but with a fentanyl dose of 15 μg/kg, 87% of patients had heart rates below 100 bpm. As a group, the percentage of patients in whom the postintubation heart rate remained below 100 bpm increased progressively with the fentanyl dose. In contrast, mean MAP fell at all dose levels after induction, the mean fall being about 30 mmHg at 5 μg/kg and greater. Mean MAP exceeded pre-induction values after intubation with 0 and 2 μg/kg, and progressive attenuation of the MAP rise was found as the dose of fentanyl increased. The percentage of patients who did not exceed their preinduction MAP rose progressively with increasing dose of fentanyl with an ED50 of 3.7 μg/kg. If a minimal fall in mean MAP after induction with no rise above preinduction MAP is the sole criterion, a fentanyl dose of about 3 μg/kg is recommended. If heart rate is to be kept below 100 bpm, a dose of at least 10 μg/kg should be used. However, this dose or greater will cause the MAP to fall in some patients to less than 70 mmHg. The choice of the most appropriate dose depends on the anaesthetist's view of the relative importance of avoiding tachycardia or hypotension in the patient with coronary artery disease.