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 both the maternal and fetal circuits as well as perfusates that approached the actual in vivo maternal/fetal protein binding gradient. Additional experiments were performed to investigate the effects of increasing maternal lidocaine concentration (5, 10, 40, 80 microg/mL) on maternal to fetal (M--F) lidocaine transfer across the human placenta. Lidocaine crossed the placenta rapidly in both the M--F and fetal to maternal (F--M) directions. When protein binding was similar in the two circuits, M--F transfer ratios (lidocaine transfer/antipyrine transfer) were significantly lower than the transfer ratios seen in the F--M direction (0.59+/-0.04 versus 0.84+/-0.06, P0.05). Transfer ratios (M--F: 0.83+/-0.06, F--M: 0.96+/-0.06) were not reduced when the physiological maternal/fetal protein binding gradient was present. Lidocaine transfer was not diminished by increasing maternal concentrations and, in contrast to bupivacaine, was not significantly affected by its binding.