[Determination of the basic data on fentanyl dosage in neuroleptanalgesia for heart surgery]

The use of high-dose fentanyl (50-150 micrograms/kg) in anaesthesia for cardiac surgery includes the need of prolonged ventilatory support in the postoperative period. Therefore, the possibility of choosing a useful dosage regimen of smaller doses of fentanyl (up to 20 micrograms/kg) leading to analgesic serum levels of greater than 3 ng/ml is investigated in this study. Fentanyl was determined by radioimmunoassay in 20 patients during and after typical cardiosurgical operations. Three bolus injections of 7 micrograms/kg were applied in the first group (n = 8). Analgesic fentanyl concentrations were reached 12-24 minutes after the first injections. The characteristic pharmacokinetic influences - especially the enlarged volume of distribution and the prolonged elimination time - were visible following repetitive doses during extracorporeal circulation. Based on these results the injection mode was changed in the second investigation group (n = 6) - 2/3 of the total dose before the start of extracorporeal circulation - resulting in analgesic fentanyl concentrations for the whole course of the operation. More stable serum levels were obtained with the combination of primary bolus injection followed by continuous infusion (3rd group, n = 6), but a higher fentanyl amount and prolonged postoperative ventilation times were registered in this group. Bolus injections adapted to the special pharmacokinetic situation seem to be the best variant for the desired effect of producing sufficient analgesic levels without long-lasting ventilatory depression with a limited total dose of fentanyl.