Effect of adrenaline on placental transfer of bupivacaine in the perfused in situ rabbit placenta.

Following general anaesthesia, each of 18 pregnant rabbits received an i.v. infusion, at a declining rate, of 0.125% bupivacaine, either plain solution followed by adrenaline (1.25 micrograms ml-1)-containing solution (n = 10) or vice versa (n = 8). All solutions contained antipyrine as an index of placental exchange. In each rabbit, a single fetal sac was opened, the umbilical vessels were cannulated and the placenta was perfused in situ with buffered Krebs solution containing Dextran. Bupivacaine and antipyrine concentrations were measured in effluent perfusate (fetal) and in maternal plasma sampled simultaneously. Mean maternal arterial pressure and mean placental perfusion pressure were not altered by adrenaline. Fetal:maternal concentration (F:M) ratios of antipyrine decreased significantly (P less than 0.05) during the second half of the experiment. In contrast, F:M ratios of bupivacaine were unchanged during the time course of the experiment and unaltered by the addition of adrenaline. It is concluded that neither adrenaline nor minor alterations in maternal placental flow affect placental transfer of bupivacaine.