Fetal cerebral oxygenation: the role of maternal hyperoxia with supplemental CO2 in sheep.

Abstract

We tested the hypothesis that supplemental CO2 can enhance the effect of maternal oxygen administration on fetal cerebral oxygenation. In near-term fetal sheep (n = 6), we instrumented the cerebral cortex with tissue PO2-laser Doppler flow probes, and placed arterial catheters. Following a 30-minute control period, the ewe breathed 50% O2 for 15 minutes, followed by added 6% CO2 for 15 minutes. We examined fetal cortical tissue PO2, cerebral blood flow (CBF), and fetal and maternal blood gases and related variables. In response to maternal O2 administration, fetal arterial PO2, O2 content, cerebral O2 delivery, and cortical tissue PO2 increased significantly. In response to supplemental CO2 inhalation, fetal cortical tissue PO2 increased further. Fetal CBF also increased in response to the elevated arterial CO2 level. CO2 supplementation of maternal O2 administration enhanced fetal cerebral oxygenation. In contrast, it was considered that during labor maternal hyperventilation with hypocapnia may blunt the effect of maternal O2 inhalation.