Cerebral metabolism during sustained hypoxemia in preterm fetal sheep.

Abstract

The purpose of this study was to determine the effect of sustained hypoxia with resulting metabolic acidosis on cerebral metabolism in the preterm ovine fetus. Twelve fetal sheep were studied at 0.75 of gestation during a normoxic control period, after 1 and 8 hours of sustained hypoxemia, and again after a 1-hour recovery period. Cerebral arteriovenous differences were analyzed for oxygen content, blood gases and pH, glucose, and lactate. Cerebral blood flow was measured with the microsphere technique. Induced hypoxemia resulted in a variable degree of fetal acidemia that was entirely metabolic. Although cerebral oxidative metabolism was well maintained throughout the study, cerebral glucose consumption was variably increased when measured after 1 hour of sustained hypoxemia, with a subsequent decrease after 1 hour of recovery. Although lactate was neither consumed nor produced during the control period, by 8 hours of hypoxic study a significant efflux of lactate from the brain was evident, which continued into the recovery period. Sustained hypoxemia results in an increase in the anaerobic metabolism of glucose by the preterm fetal brain independent of any change in cerebral oxidative metabolism, which may give rise to an accumulation of lactic acid and contribute to neurologic impairment.