Effect of Exteriorization of the Sheep Fetus on Its Cardiovascular Function

Abstract

Exteriorized sheep or goat fetuses, with placental circulation continuing, have been extensively used for measurements of fetal cardiovascular function. However, the effects of this procedure on fetal cardiovascular function have not been assessed. We inserted vinyl catheters into an umbilical vein, an umbilical or fetal hindlimb artery, and a hindlimb vein. We measured umbilical arterial and venous blood gas tensions, umbilical blood flow using the steadystate diffusion antipyrine method, and fetal arterial and umbilical venous pressures before and after delivery by cesarean section. Following exteriorization, placental vascular resistance consistently increased and umbilical blood flow decreased. Umbilical venous Po₂ increased, but umbilical arterial and venous pH and Pco₂ and arterial Po₂ did not change significantly. Thus exteriorization of the fetus produces major changes in the fetal circulation, but these changes are not indicated by any major alterations in fetal blood gases and pH.