THE PLACENTAL-TRANSFER OF SUFENTANIL - EFFECTS OF FETAL PH, PROTEIN-BINDING, AND SUFENTANIL CONCENTRATION

This study investigated factors that influence the placental transfer of sufentanil using the dual-perfused, single-cotyledon human placenta l model. Placentas were collected from healthy women. Experiments were designed to elucidate the effects of maternal protein binding, changi ng maternal sufentanil concentration (1, 10, 20, and 100 ng/mL) and de creasing fetal pH (fetal acidemia 7.2, 7.0, 6.8) on the placental tran sfer of sufentanil. Sufentanil crossed the placenta rapidly at a rate two-thirds that of the transfer marker, antipyrine. Sufentanil transfe r increased linearly with the maternal concentration (r = 0.999). Sufe ntanil/antipyrine maternal to fetal (M-->F) transfer ratios were signi ficantly reduced (0.66 +/- 0.05 vs 0.40 +/- 0.04, P < 0.05) when fresh frozen plasma was added to the maternal circuit to enhance protein bi nding. Fetal pH and sufentanil transfer were related because sufentani l M-->F clearance increased significantly as the fetal pH decreased (r = 0.973, P < 0.05). Sufentanil appears to cross the placenta by passi ve diffusion but is modulated by the degree of maternal protein bindin g. Sufentanil M-->F transfer is enhanced by fetal acidemia.