CEREBRAL OXIDATIVE-METABOLISM IN FETAL SHEEP WITH PROLONGED AND GRADED HYPOXEMIA

Cerebral oxidative metabolism and associated circulatory responses wer e determined in 14 unaesthetized fetal sheep near term, during a normo xic control period and subsequently, during four days of prolonged and graded hypoxemia induced by progressively lowering maternal inspired oxygen concentration with 1-2% CO2 added; first day 18%, second day 16 %, third day 12-14%, fourth day 10-12%. Preductal arterial and sagitta l vein blood samples were analyzed for oxygen content, blood gas tensi ons and pH. Regional blood flow was measured with a microsphere techni que. Cerebral blood flow increased in a stepwise manner with the grade d reduction in fetal arterial O2 saturation and continued to be well p redicted by blood gas and metabolic alterations, with no adaptive chan ge evident. Cerebral oxidative metabolism remained little changed with chronically induced hypoxemia until arterial O2 saturation was less t han 30% and with fetal acidemia evident when decreased to 70% of normo xic control values. Whether the decrease in oxidative metabolism by th e brain at this time represents an adaptive response whereby growth an d functional alterations lead to a decrease in nonessential energy uti lization or rather a pathological change, remains to be determined.