Cerebral oxygen metabolism after aneurysmal subarachnoid hemorrhage

Previous studies of cerebral oxygen metabolism and extraction in patients with subarachnoid hemorrhage (SAH) have yielded conflicting results. We used positron emission tomography (PET) to measure the regional cerebral metabolic rate for oxygen (rCMRO₂). oxygen extraction fraction (rOEF), and cerebral blood flow (rCBF) 16 times in 11 patients with aneurysmal SAH. All studies were performed preoperatively: no patient had hydrocephalus or intracerebral hematoma on brain CT. Eight patients with no arteriographic vasospasm who were studied on days 1-4 post-SAH had a significant 25% reduction in global CMRO₂ compared to age-matched controls, and no significant change in global OEF, sug-gesting a primary reduction in CMRO₂ caused by SAH. Four patients studied seven times during arteriographic vasospasm had significantly increased rOEF with unchanged CMRO₂ in arterial territories affected by arteriographic vasospasm compared to territories without vasospasm. indicative of cerebral ischemia without infarction. No brain regions studied with PET were infarcted on follow-up CT. We conclude that the initial aneurysm rupture produces a primary reduction in CMRO₂, and that subsequent vasospasm causes ischemia.