ABSTRACT
Maternal critical illness and hypoxia affect oxygen delivery to the fetus. The placenta is capable of buffering this impact, first through hemodynamic adaptation, then metabolic adaptation, thereby preserving fetal oxygen supply. The dynamics of oxygen carriage by fetal hemoglobin also protect fetal oxygenation during maternal hypoxemia. Fetal hemodynamic adaptation redistributes blood flow to essential organs, thus sparing the brain from hypoxia. However, below a critical threshold, neither the placenta nor the fetus can protect fetal organs from the consequences of impaired maternal oxygenation, as maternal hemodynamic adaptation reverts blood flow from the uterus to her own essential organs and the fetus is no longer buffered.
Medical management of maternal critical illness must consider the complex physiological changes in cardiorespiratory function occurring during pregnancy, as well as the hemodynamic significance of the placental circuit. In this chapter, we review the susceptibility of pregnant women to respiratory illness, the impact of maternal hypoxia due to illness or altitude on placental function, and the various modes of respiratory and cardiac supportive care used during maternal intensive care, with their impacts on maternal and fetal physiology. We also examine maternal environmental exposures that can alter placental function or fetal oxygen carrying capacity, including wildfire smoke, smoking/vaping, and carbon monoxide intoxication.
