CEREBRAL METABOLISM DURING SUSTAINED HYPOXEMIA IN PRETERM FETAL SHEEP

OBJECTIVE: The purpose of this study was to determine the effect of su stained hypoxia with resulting metabolic acidosis on cerebral metaboli sm in the preterm ovine fetus. STUDY DESIGN: Twelve fetal sheep were s tudied 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 co ntent, blood gases and pH, glucose, and lactate. Cerebral blood flow w as measured with the microsphere technique. RESULTS: Induced hypoxemia resulted in a variable degree of fetal acidemia that was entirely met abolic. Although cerebral oxidative metabolism was well maintained thr oughout 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 consum ed nor produced during the control period, by 8 hours of hypoxic study a significant efflux of lactate from the brain was evident, which con tinued into the recovery period. CONCLUSION: Sustained hypoxemia resul ts in an increase in the anaerobic metabolism of glucose by the preter m fetal brain independent of any change in cerebral oxidative metaboli sm, which may give rise to an accumulation of lactic acid and contribu te to neurologic impairment.