Transfer of lidocaine across the dual perfused human placental cotyledon

Factors affecting lidocaine transfer across the normal term human placenta were studied using the dual perfused isolated single cotyledon. Experiments were performed using perfusates which provided equal protein binding in bo th the maternal and fetal circuits as well as perfusates that approached th e actual in vivo maternal/fetal protein binding gradient. Additional experi ments were performed to investigate the effects of increasing maternal lido caine concentration (5, 10, 40, 80 mu g/mL) on maternal to fetal (M-->F) li docaine transfer across the human placenta. Lidocaine crossed the placenta rapidly in both the M-->F and fetal to maternal (F-->M) directions. When pr otein binding was similar in the two circuits, M-->F transfer ratios (lidoc aine transfer/antipyrine transfer) were significantly lower than the transf er ratios seen in the F-->M direction (0.59+/-0.04 versus 0.84+/-0.06, P<0. 05). Transfer ratios (M-->F: 0.83+/-0.06, F-->M: 0.96+/-0.06) were not redu ced when the physiological maternal/fetal protein binding gradient was pres ent. Lidocaine transfer was not diminished by increasing maternal concentra tions and, in contrast to bupivacaine, was not significantly affected by it s binding.