Transplacental diffusion of ethanol under steady state conditions

The placental clearances of ethanol and antipyrine, uterine and umbilical blood flows (ml/min) were measured in six chronic sheep preparations. The two substances were infused simultaneously at constant rate into the fetal inferior vena cava. In the steady state, blood samples were obtained from the fetal abdominal aorta, common umbilical vein, maternal uterine vein and maternal femoral artery and analysed for the blood concentrations of ethanol and antipyrine. The clearance of ethanol (CE) was related to uterine (F) and umbilical (f) blood flows according to the regression equation: CE = -26 + 0.88 (F x f)/(F + f), (r = 0.987). The ethanol/antipyrine clearance ratio ranged between 1.21 and 0.97 (mean 1.07, 95% confidence limits 1.01-1.14) These data support the hypothesis that the placental clearance of ethanol is primarily flow-limited.