Hyperthermia Prevent Metabolic and Cerebral Flow Responses to Hypoxia in the Fetal Sheep

Abstract

Objective: Fetal brain temperature has been found to decrease during hypoxia, strongly suggesting a reduction in cerebral O₂ consumption and increases in cerebral blood flow. These responses may protect the brain in part against hypoxic injury. This study was undertaken to examine whether these compensatory mechanisms are lost during fetal hyperthemia.

Methods: Intermittent fetal hypoxemia was induced by administering low-O₂ gas mixtures to nine neart-term ewes Fetal brain and body core temperature responses were measured with and without fetal hyperthermia induced by circulating warm water through a plastic coil looped about the fetus in utero.

Results: In normothermic fetuses, fetal brain temperature relative to core decreased during a 30-minute period of hypoxia and then returned to normal during recovceyr. This response may be explaiend by a combination of cerebral hypometabolism and increased cerebral blood flow. However, in hyperthemic fetuses (intrauterine warming for 1 hour, raising body core and brain temperatures 0.66 ± 0.06 and 0.61 ± 0.10C, respectively) a subsequent period of hypoxia no longer induced a reduction in brain temperature relative to body core.

Conclusion: When temperature of the fetal sheep is elevated, as may occur with maternal fever, prolonged exercise, and elevated environmental temperatures, the fetal brain is less well protected against hypoxic injury.