Effects of maternal hyperventilation on uterine blood flow and fetal oxygenation and acid base status

Abstract

Changes in uterine blood flow and fetal oxygenation were studied in unanesthetized pregnant ewes following mechanical hyperventilation with hypocapnia. In order to evaluate the individual effects of maternal hypocapnia and positive pressure ventilation, CO2 was added to the inspired air during mechanical ventilation to produce normocapnia and hypercapnia. Uterine blood flow decreased approximately 25% during all hyperventilation periods. Since the reduction in uterine blood flow was unrelated to changes in maternal Pa(CO2) (range 17 to 64 torr) or pH (range 7.74 to 7.24), the decrease probably was caused by the mechanical effect of IPPB. Maternal respiratory alkalosis, on the other hand, decreased fetal arterial oxygen saturation 23%.