[Use of fentanyl for anesthesia induction in cesarean section. Pharmacokinetics and pharmacodynamics in mother and child].

A group of 36 patients in the last trimester of pregnancy and scheduled for cesarean section were examined during the induction of standardized general anesthesia (methohexitone 1.5 mg/kg, succinylcholine 1.5 mg/kg). No other inhalation anesthetics than N2O/O2 (50%:50%) were administered. In addition, 18 of the women received 0.005 mg/kg fentanyl prior to intubation. The remaining 18 patients served as a control group. In the study group maternal fentanyl plasma levels were determined 1 min after injection and again at the time of omphalotomy (radioimmunoassay). Immediately after clamping of the umbilical cord the fetal fentanyl plasma levels and the pH, pCO2 and pO2 values in both umbilical vein and artery were measured. The feto-maternal ratio and the fetal uptake were calculated. RESULTS. Maternal fentanyl plasma levels decreased significantly, from 7.84 (3.55-17.24) ng/ml 1 min after injection to 5.92 (2.01-14.15) ng/ml during omphalotomy. The corresponding fentanyl plasma levels in the umbilical vein were 2.08 (0.88-3.42) ng/ml. The feto-maternal ratio was 0.44 (0.08-1.00). The induction-delivery time ranged from 2 to 8 min. There was a significant correlation between umbilical-venous fentanyl concentration and the induction-delivery time: the longer the induction-delivery time the lower the fentanyl concentration in the umbilical vein. The 1-min Apgar score was 8 (5-9), the 5-min Apgar score 9 (8-10) and the 10-min Apgar score 10 (9-10) in neonates born to the fentanyl group. Only the 1-min Apgar score was significantly lower than in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)