Cardiac output and blood flow volume redistribution during acute maternal hypoxia in fetal sheep

Abstract

Objective: Acute hypoxia is one of the main causes of poor neonatal outcome. The aim of this study was the investigation of cardiac output (CO) and blood flow redistribution following induction of acute hypoxia in a fetal sheep model.

Method: We investigated 10 fetal sheep between 108 and 130 days of gestation. Acute hypoxia was induced by reducing the O₂ saturation in the ventilated gas mixture of the maternal sheep to ∼75%. The CO, placental fraction of CO, Doppler parameters in the ductus venosus (DV), umbilical artery (UA) and vein (UV) were measured.

Results: The fetal pO₂ decreased from 47.1 (7.19; 7.35) to 6.89 (6.78; 7.11) mm Hg [P=0.01, median, (95% CI)] during hypoxia. Fetal pH and BE were also significantly reduced. The DV/UV fraction increased from 15.3 (11.5; 19.8) to 51.1 (35.9; 62.1) (P=0.0001). The combined cardiac output [1228.1 (1024.3; 1686.4) vs. 987.8 (834, 1261) mL min^–1], the placental fraction of the CO [31.5 (26; 42.1) vs. 26.9 (20.6; 29.3)%] and the right to left (R/L) heart ratio [1.76 (1.5; 2.2) vs. 1.3 (1.1; 1.6)] significantly decreased during hypoxia.

Conclusions: Acute hypoxia significantly increases the proportion of the placental blood passing through the DV and reduces the placental fraction of CO and the R/L heart ratio. These findings could be used as early signs of acute fetal hypoxia.