Pharmacokinetics of alfentanil and clinical responses during cardiac surgery

This study assessed the pharmacokinetic and pharmacodynamic behaviour of alfentanil during and after coronary artery bypass grafting (CABG). Twenty-eight patients with good ventricular function having CABG were divided into three groups and premedicated with morphine 0.1 mg · kg−1 IM, scopolamine 0.005 mg · kg−1 IM and diazepam 0.1 mg · kg−1 PO. Group I patients received an infusion of 250 μg · kg−1 of alfentanil over one hour coincidental with a second infusion at 2.5 μg · kg−1 · min−1 which was continued to the end of surgery. Patients in group II received 300 μg · kg−1 and 3.0 μg · kg−1 · min−1 and patients in group III 350 μg · kg−1 and 3.5 μg · kg−1 · min−1. The tracheas of all patients were intubated after receiving alfentanil 96 μg-kg−1 and pancuronium 0.15 μg · kg−1. Haemodynamic responses to intubation and surgical stimuli (≥ 20 per cent increase in heart rate and/or systolic blood pressure from control) were treated with isoflurane, one to two per cent inspired, until abolished. Blood samples were taken during and after surgery for plasma alfentanil concentrations which were determined by radioimmunoassay. After surgery the times to awakening and extubation, and alfentanil elimination half-life (t1/2B = 0.6931−k) were determined for each patient. Haemodynamic responses occurred in 20 patients. There were no significant differences in any variable among the groups. The times to awakening and extubation for all patients were 3.2 ± 0.6 and 8.8 ± 1.2 hr (mean ± SEM) respectively. The elimination half-life for all patients was 5.1 ± 1.0 hr(mean ± SEM). We conclude that alfentanil given at these rates of infusion provides inadequate adrenergic suppression for CABG yet does not allow early postoperative tracheal extubation. The elimination half-time appears prolonged after cardiopulmonary bypass compared with values obtained from volunteers or from patients undergoing non-cardiac surgery.