Intraoperative mild hypothermia ameliorates postoperative cerebral blood flow impairment in patients with aneurysmal subarachnoid hemorrhage

OBJECTIVE: Intraoperative mild hypothermia has been used during cerebral aneurysm surgery to reduce ischemic injury induced by temporary vessel occlusion and brain retraction. However, the clinical effects on cerebral hemodynamics are unclear. This study investigated the effects of intraoperative mild hypothermia on cerebral blood flow (CBF) after surgery to treat aneurysmal subarachnoid hemorrhage. METHODS: Twenty-four patients with ruptured internal carotid or middle cerebral artery aneurysms, of preoperative Hunt and Hess Grade II or Ill, underwent aneurysm clipping within 72 hours after the onset of subarachnoid hemorrhage. During surgery, patients were randomly assigned to either intraoperative mild hypothermia (33.5 degrees C, n = 12) or normothermia (37 degrees C, n = 12). Brain single photon emission computed tomography with Tc-99m-hexamethylpropylenamine oxime or (TC)-T-99m-L,L-ethylcysteinate dimer was performed on Days 4, 7, and 14 after subarachnoid hemorrhage. Regional CBF was determined in the basal ganglia and cingulate, frontal, and frontoparietal cortices, using a semiquantitative method. RESULTS: CBF in the frontal cortex ipsilateral to the aneurysm was significantly higher in the hypothermia group than in the normothermia group on Day 4 (P < 0.01) but not Day 7 or 14. There was a similar trend in the ipsilateral frontoparietal cortex, but it was not significant. There were no differences in regional CBF in the ipsilateral cingulate cortex or basal ganglia or in any contralateral region during the study period. CONCLUSION: Intraoperative mild hypothermia may reduce the severity of ischemia induced by intraoperative temporary vessel occlusion and brain retraction, thus ameliorating postoperative CBF impairment.