Maternal, fetal and placental distribution of lidocaine-epinephrine and bupivacaine after epidural administration for cesarean section

Bupivacaine and lidocaine are both lipophilic drugs, bupivacaine being more lipophilic and protein-bound. Our earlier studies, using human placenta perfused in vitro, showed that increased placental binding of bupivacaine restricts fetal transfer compared to the higher fetal transfer of lidocaine. However, placental tissue concentrations of local anesthetics have not been determined in the clinical context. Term parturients were randomized to receive either 2% lidocaine-epinephrine (n = 10) or 0.5% bupivacaine (n = 10) through a lumbar epidural catheter for elective cesarean section. Total drug concentrations of lidocaine and bupivacaine in maternal and umbilical plasma and placental tissue were determined. There was a higher incidence of maternal hypotension in the lidocaine-epinephrine group than in the bupivacaine group (7/10 vs 1/10, P < 0.05). At delivery, fetal/maternal ratios for total concentrations of lidocaine and bupivacaine were similar (0.49 vs 0.42. The mean placental tissue/maternal plasma concentration ratio of lidocaine was higher than that of bupivacaine (1.45 vs 1.01, P < 0.05). The mean amount of the drug retained in the placenta per unit of dose (mg/kg) was also higher in the lidocaine-epinephrine group, although this difference did not reach statistical significance (0.46 mg/unit dose vs 0.40 mg/unit dose). Values for area under the concentration-time curves per unit of dose were similar. In conclusion, maternal plasma concentrations, fetal/maternal concentration ratios and placental tissue binding of lidocaine resembled those of bupivacaine after epidural administration. These findings are probably explainable by the effect of maternal hypotension on the distribution of lidocaine.