Fetal and neonatal brain oxygen

¹ Developmental and Sensory Physiology Laboratory, Childrens Hospital of Los Angeles, Los Angeles, California

Brain oxygen availability (aO₂) in the mature and immature fetus, neonate, and adult guinea pig was measured by a polarographic technique. Because of the similarity of fetal and maternal brain aO₂ levels at various atmospheric pO₂, and the marked drop in fetal brain aO₂ after surgical and mechanical trauma, it was concluded that under normal physiological conditions fetal blood pO₂ is probably higher than usually reported. As the effects of Apresoline, Pitressin, Adrenalin, and noradrenaline were similar in the adult and neonate shortly after delivery, it was concluded that the different effects seen in the fetus in utero were not due to qualitative differences in reactivity of fetal and maternal tissues. Autonomic reflexes play an important role in the changes in brain aO₂ occurring with increased intracranial pressure. Bradycardia appears early with compression of the head and late in anoxic anoxia. The normal intracranial pressure in the guinea pig was approximately 9 mm Hg and was higher than the hydrostatic pressure of the cochlea, findings which are compatible with the existence of an open channel between cerebrospinal fluid and perilymph.