Umbilical vein infusion of prostaglandin I2 increases ductus venosus shunting of oxygen‐rich blood but does not increase cerebral oxygen delivery in the fetal sheep

Abstract

Key points The ductus venosus (DV) is a dynamic fetal shunt that allows substrate-rich blood from the umbilical vein to bypass the hepatic circulation. In vitro studies suggest a direct role of prostaglandin I₂ (PGI₂) in the regulation of DV tone; however, the extent of this regulation has not been determined in utero. 4D flow and T₂ oximetry magnetic resonance imaging can be combined to determine blood flow and oxygen delivery within the fetal circulation. PGI₂ increases DV shunting of substrate-rich blood but this does not increase cerebral oxygen delivery. Abstract During fetal development, the maintenance of adequate oxygen and nutrient supply to vital organs is regulated through specialized fetal shunts. One of these shunts, the ductus venosus (DV), allows oxygen-rich blood to preferentially stream from the placenta toward the heart and brain. Herein, we combine magnetic resonance imaging (MRI) techniques that measure blood flow (4D flow) and oxygen saturation (T₂ oximetry) in the fetal circuit to determine whether umbilical vein infusion of prostaglandin I₂ (PGI₂, regulator of DV tone ex utero) directly dilates the DV and thus increases the preferential streaming of oxygen-rich blood toward the brain. At 114–115 days gestational age (dGA; term = 150 days), fetal sheep (n = 6) underwent surgery to implant vascular catheters in the fetal femoral artery, femoral vein, amniotic cavity and umbilical vein. Fetal MRI scans were performed at 119–124 dGA. 4D flow and T₂ oximetry were performed to measure blood flow and oxygen saturation across the fetal circulation in both a basal state and whilst the fetus was receiving a continuous infusion of PGI₂. The proportion of oxygenated blood that passed through the DV from the umbilical vein was increased by PGI₂. Cerebral oxygen delivery was unchanged in the PGI₂ state. This may be a result of decreased flow from the right to left side of the heart as blood flow through the foramen ovale was decreased by PGI₂. We have shown that although PGI₂ acts on the DV to increase the proportion of oxygen-rich blood that bypasses the liver, this does not increase cerebral oxygen delivery in the fetal sheep.