Arterial blood gases will show PCO2 levels of 25-30 mmHg. There will also be an increase in oxygen demand by the maternal organs, the placenta and the growing fetus. As the uterus enlarges the abdominal organs are displaced upwards causing diaphragm elevation. Because of the increased oxygen demand and the reduction in FCR there is a decreased oxygen reserve predisposing the pregnant patient to hypoxia. It would not be unreasonable to assume that all pregnant trauma patients are hypoxic.
Hypoxia can lead to vasoconstriction of uterine blood flow to the fetus.
Supplemental oxygen should always be provided and do not hesitate to assist ventilations when necessary. It is important to be aware that during pregnancy, vascular congestion in the upper respiratory passages makes the pregnant patient more prone to nasopharyngeal bleeding. Inserting nasal airways or nasal endotracheal tubes should be performed with extreme caution or avoided altogether. To accommodate this, the cardiac output increases 1-1.5 liters per minute. Toward term the blood pressure will return to prepregnancy levels.