Maternal hypocapnia and fetal hypoxia.

    

    Maternal hypocapnia, conversely, may be associated with fetal hypoxia and acidosis.

Try to avoid hyperventilation during general anesthesia!

    Three mechanisms have been suggested for this:

•  maternal hypocapnia (< 25 mmHg) causes uterine and umbilical vessel vasoconstriction;

• mechanical hyperventilation increases intrathoracic pressure and reduces venous return as well as cardiac output and thus reduces uteroplacental blood flow; 

•  maternal alkalosis shifts the oxygen–hemoglobin dissociation curve to the left, reducing fetal extraction of oxygen.

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