Hyperthermia prevents metabolic and cerebral flow responses to hypoxia in the fetal sheep

OBJECTIVE: Fetal brain temperature has been found to decrease during hypoxi a, strongly suggesting a reduction in cerebral O-2 consumption and increase s in cerebral flow. These responses may protect the brain in part against h ypoxic injury. This study was undertaken to examine whether compensatory me chanisms are lost during fetal hyperthermia. METHODS: Intermittent fetal hypoxia was induced by administering low O-2 ga s mixtures to nine near term ewes. Fetal brain and body core temperature we re 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 recovery. This response may be explained by a combination of cerebra l hypometabolism and increased cerebral blood flow. However, in fetuses(int rauterine 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 l onger induced a reduction in brain temperature relative to body core. CONCLUSION: When temperature of the fetal sheep is elevated, as may occur w ith fever, prolonged exercise, an elevated environmental temperatures, the fetal brain is less well protected against hypoxic injury. Copyright (C) 20 00 by the Society for Gynecologic Investigation.