Cerebral circulation and metabolism in the acute stage of subarachnoid hemorrhage

Object. The mechanism of reduction of cerebral circulation and metabolism i n patients in the acute stage of aneurysmal subarachnoid hemorrhage (SAH) h as not yet been fully clarified. The goal of this study was to elucidate th is mechanism further. Methods. The authors estimated cerebral blood flow (CBF), cerebral metaboli c rate of oxygen (CMRO2), O-2 extraction fraction (OEF), and cerebral blood volume (CBV) preoperatively in eight patients with aneurysmal SAH tone man and seven women, mean age 63.5 years) within 40 hours of onset by using po sitron emission tomography (PET). The patients' CBF, CMRO2, and CBF/CBV wer e significantly lower than those in normal control volunteers. However, OEF and CBV did not differ significantly from those in control volunteers. The significant decrease in CBF/CBV, which indicates reduced cerebral perfusio n pressure, was believed to be caused by impaired cerebral circulation due to elevated intracranial pressure (ICP) after rupture of the aneurysm. In t wo of the eight patients, uncoupling between CBF and CMRO2 was shown, stron gly suggesting the presence of cerebral ischemia. Conclusions. The initial reduction in CBF due to elevated ICP, followed by reduction in CMRO2 at the time of aneurysm rupture may play a role in the d isturbance of CBF and cerebral metabolism in the acute stage of aneurysmal SAH.