Relation between cerebral oxygen delivery and neuronal cell damage in fetal sheep near term

Asphyxia is one of the major causes for fetal brain damage. Although the quality of life of the so affected children is mostly very limited, the pathogenesis of hypoxic fetal brain damage is poorly understood. Particularly, there is a lack of studies, in which cerebral oxygen delivery is directly correlated to the extent of neuronal cell damage in the same brain specimens. Therefore, we measured cerebral oxygen delivery before (-1 h), during (+3 min & +27 min) and after (+10 min, +4 h, +72 h) 30 min of ischaemia in 5 chronically catheterized normoxemic fetal sheep at 129+/-1 days gestation (term is at 147 days) using the microsphere method. In contrast to previous studies (Williams et al. 1990), we arrested carotid arterial blood flow above the lingual artery for 30 min during surgery. Seventy-two hours later the fetal brains were fixed in vivo under barbiturate anaesthesia of both the fetus and the ewe. After cerebral blood flow analysis neuronal cell damage was assessed with light microscopy in 43 specimens of the fetal brain after cresyl violet/fuchsin staining using a scoring system. After arrest of carotid arterial blood flow cerebral blood flow was reduced by 80%. Neuronal cell damage was focussed on the cerebral cortex. Almost no damage could be detected in deeper parts of the brain. In the cerebrum there was a threshold oxygen delivery of 3 mi O-2/100 g tissue/min, below which neuronal damage occurred. However, there was no correlation between cerebral oxygen delivery and neuronal cell damage in specimens of the cerebrum, in which oxygen delivery was less than 3 mi O-2/100 g tissue/min, suggesting selective vulnerability. Therefore, in addition to the reduction in cerebral oxygen delivery, other variables, e.g. neurotransmitter release, receptor pattern or oxygen radicals, may be involved in the development of brain damage.