Fentanyl pharmacokinetics and hemodynamic effects in preterm infants during ligation of patent ductus arteriosus

A bolus of 30 μg.kg^-1 fentanyl was given to 9 preterm infants (gestational age 31.8 ± 4.7 weeks, weight 1100 ± 309 g) for induction of anesthesia for ligation of a patent ductus arteriosus. Thirty minutes after the injection, fentanyl plasma concentrations were between 7.7 and 13.6 ng.ml^-1. Elimination half-life was 6-32 hr (mean ± SD, 17.7 ± 9.3). Systolic blood pressure remained stable throughout surgery. There was a gradual increase in heart rate from 159 ± 12 min^-1 at the time of skin incision to 173 ± 15 min^-1 at the time of skin closure (P < 0.05). Fentanyl plasma concentrations remained virtually unchanged between 30 min (10.6 ± 1.9 ng.ml^-1) and 120 min (9.6 ± 1.6 ng.ml^-1); whereas at the end of surgery most infants moved and breathed spontaneously. This phenomenon can be explained by redistribution of fentanyl from brain into pharmacodynamically inert tissues.