The effect of graded hypothermia on hypoxic-ischemic brain damage: a neuropathologic study in the neonatal rat.

To investigate the relationship between neuropathologic damage and cerebral metabolic alterations during hypothermia in the neonatal animal, 7 day old Sprague-Dawley rats were subjected to unilateral common carotid artery ligation and hypoxia at 37 degrees C, 29 degrees C, and 21 degrees C. At 37 degrees C, animals had extensive infarction of tectum and ipsilateral cerebral hemisphere, and marked depletion of brain ATP. At 29 degrees C, there was no significant change in brain ATP; neuropathologic damage was limited to a few areas of necrosis in the deeper layers of cerebral cortex. No histologic injury was seen in the 21 degrees C group of rats. Profound hypothermia may prevent cerebral edema and visible neuropathologic damage associated with hypoxic-ischemic injury by decreasing cerebral metabolic demands. Moderate hypothermia confers a partial, but incomplete degree of protection; whereas during normothermia, the full extent of hypoxicischemic injury is manifest.