Transfer of lidocaine across the sheep placenta to the fetus. Hemodynamic and acid-base responses of the fetal lamb.

Placental transfer of lidocaine administered to pregnant sheep and removal of the drug from the fetal circulation were determined. Responses of the hemodynamic and acid-base state in the mother and fetus were also studied. Lidocaine readily crossed the placenta and appeared in the fetal blood as early as one minute following injection. Disappearance of lidocaine in the asphyxiated fetus tended to be slower than in the normal one. Lidocaine produced a transient fall in the fetal heart rate which was accompanied by a decrease in blood pH and oxygenation. Lidocaine also reduced umbilical blood flow and, in some instances, uterine blood flow. Decrease in umbilical blood flow was more pronounced in the initially asphyxiated fetus.