The Effect of Changes in Maternal pH and PCO2 on the PO2 of Fetal Lambs

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Abstract
The effect on the fetus of changes in maternal PCO2 [carbon dioxide pressure] and pH were studied in sheep. Maternal hyperventilation without changes in PCO2 and PH had no significant effect while hyperventilation associated with nypocapnia and respiratory alkalemia was associated with a consistent decrease in fetal PO2 [oxygen pressure] and SO2 [oxygen saturation]. Fetal PO2 also decreased with maternal metabolic alkalemia indicating that the cnange in maternal pH, rather tha PCO2, was the critical factor influencing fetal PO2. Maternal hypercapnia with acidemia was associated with a significant increase in fetal PO2 and SO2. These changes in fetal PO2 and SO2 were the combined effect of alterations in O2 transfer within the placenta and changes in umbilical blood flow. Prolonged maternal hyperventilation associated with alkalemia resulted in severe fetal hypoxia, metabolic acidosis and fetal distress. Reports concerning parturient women and their fetuses indicate that there is a similar relationship between maternal pH and fetal PO2 in man and that this is of clinical importance.