Search

Background Fetal acidemia increases umbilical venous bupivacaine concentrations in the in situ rabbit model. The authors studied the effects of decreasing fetal pH on the rate of maternal to fetal (M-->F) clearances of lidocaine, bupivacaine, 2-chloroprocaine, and antipyrine (a nonionic marker of placental transfer) across the isolated, dual perfused, human placental cotyledon. Methods Maternal to fetal clearances of bupivacaine, lidocaine, 2-chloroprocaine, and antipyrine were determined at fetal pH (7.4), during progressive fetal acidemia (pH 7.2-->7.0-->6.8), and after recovery to fetal pH 7.4 in experiments with both low protein state and in those with in vivo maternal and fetal protein-binding potentials. Results Placental transfer of all three agents increased linearly as the fetal pH decreased. Antipyrine transfer was unaffected. Clearance of lidocaine and bupivacaine, but not 2-chloroprocaine, returned to baseline when fetal pH was restored to 7.4. When maternal and fetal protein-binding potentials were increased, clearance at fetal pH 7.4 of bupivacaine, but not lidocaine, decreased significantly. During fetal acidemia, the transfer of both agents increased, but to a lesser extent than in the low protein concentration experiments. Conclusions Increasing the pH difference between maternal and fetal perfusates promotes M-->F passage of unionized lidocaine, bupivacaine, and 2-chloroprocaine. This likely results from an increased proportion of ionized local anesthetic in the acidemic fetal perfusate and consequent widening of the M-->F concentration gradient of the unionized form. Transfer of lidocaine and bupivacaine was limited by the maternal protein binding.

Background Bupivacaine is widely used for obstetric analgesia, yet published information on the mechanism of human placental bupivacaine transfer is sparse. The dual perfused human placental model was used to elucidate the factors governing the placental transfer of bupivacaine. Methods Bupivacaine transfer was studied using the recirculating (closed) model and the single pass (open) model. Single placental cotyledons were perfused with either heparinized Krebs-Ringer's buffer (KRB) supplemented with human albumin (fetal and maternal circuits) or 100% fresh frozen plasma (maternal circuit) to control the bupivacaine protein binding in those circuits. In the open model, bupivacaine clearance was compared before and after being subjected to either increasing concentrations of bupivacaine or its structural analog, mepivacaine. Results For those studies in which the maternal and fetal protein binding was equal, the maternal to fetal (M-->F) transfer was significantly greater (P < 0.05) than that in the fetal to maternal (F-->M) direction. When the perfusates were modified to simulate actual in vivo plasma protein concentrations, bupivacaine transfer was shown to be related to the degree of protein binding found in the two circuits. In the open studies, bupivacaine transfer was similar at all concentrations investigated, unaffected by mepivacaine, and related to the pH of the fetal perfusate. A concentration effect was seen within the placental tissue at the end of the experiment. Conclusions Bupivacaine placental transfer characteristics suggest passive diffusion rather than active drug transport and appear to be influenced by the maternal and fetal plasma protein binding, fetal pH, and placental uptake.

Increasing the resting lower esophageal sphincter (LES) tone is a useful method of preventing gastroesophageal reflux. The effects of a new antiemetic, domperidone, on LES were studied in 28 subjects. Group I included eight normal nonpregnant control subjects. The remaining 20 pregnant women were divided into two groups, Group II and III--ten parturients without and ten with symptoms of heartburn. Domperidone increased LES pressure by 19, 11 and 10 cm H2O in Groups I, II and III, respectively (P less than 0.05). Domperidone may be a valuable premedicant in some patients to decrease the chance of gastro-esophageal reflux.