INTRAVENOUS REMIFENTANIL - PLACENTAL-TRANSFER, MATERNAL AND NEONATAL EFFECTS

Background: Remifentanil has not been studied in obstetric patients. T his study evaluates the placental transfer of remifentanil and the neo natal effects when administered as an intravenous infusion. Methods: N ineteen parturients underwent nonemergent cesarean section with epidur al anesthesia and received 0.1 mu g.kg(-1).min(-1) remifentanil intrav enously, which was continued until skin closure. Maternal arterial (MA ), umbilical arterial (UA), and umbilical venous (UV) blood samples we re obtained at delivery for analysis of drug concentrations of remifen tanil, its metabolite, and blood gases. Maternal vital signs were moni tored continuously, and pain and sedation levels were assessed intermi ttently. Apgar scores were obtained at 1, 5, 10, and 20 min, and Neona tal and Adaptive Capacity Scores were noted 30 and 60 min after delive ry. Parturients and newborns mere observed for at least 24 h after sur gery for side effects. Results: The means and SDs of UV:MA and UA:UV r atios for remifentanil were 0.88 +/- 0.78 and 0.29 +/- 0.07, respectiv ely. Mean clearance was 93 ml.min(-1).kg(-1). The mean UV:MA and UA:MV ratios for remifentanil acid were 0.56 +/- 0.29 and 1.23 +/- 0.89, re spectively, The mean MA (remifentanil acid):MA (remifentanil) ratio wa s 2.92 +/- 3.65. There were no adverse effects on the neonates, but th ere was a sedative effect and respiratory depressant effect on the mot hers. Conclusions: Remifentanil crosses the placenta but appears to be rapidly metabolized, redistributed, or both. Maternal sedation and re spiratory changes occur, but without adverse neonatal or maternal effe cts.