Postischemic treatment with hypothermia improves outcome from incomplete cerebral ischemia in rats

It is known that hypothermia can improve outcome when induced during ischemia. We evaluated whether hypothermia can decrease ischemic injury if it is induced after incomplete ischemia. Rats were anesthetized with 1.4% inspired isoflurane, and ischemia was produced by right carotid ligation combined with hemorrhagic hypotension to 30 mm Hg for 30 min. Hypothermia (31 degrees C) was induced or normothermia (37 degrees C) was maintained for 1 h after completion of the ischemic challenge. Isoflurane anesthesia was maintained during this period. Five of 15 normothermic rats and 3 of 15 hypothermic rats died of stroke after ischemia. For all rats tested, hypothermic-treated animals had a significantly better neurologic outcome than normothermic rats (p less than 0.05). Histopathology showed a correlation of r = 0.67 (p less than 0.05) with neurologic outcome, and neuronal damage was significantly worse in normothermic compared with hypothermic rats (p less than 0.05). These results show that postischemic hypothermia will decrease neuronal injury and improve neurologic outcome associated with incomplete ischemia.