Hyperventilation-induced cerebral ischemia in patients with acute brain lesions: demonstration by xenon-enhanced CT.

PURPOSE To examine the possibility that hyperventilation, commonly used to prevent or treat increased intracranial pressure in patients with acute brain lesions, may induce significant cerebral ischemia. METHODS Local cerebral blood flow and vascular reactivity were measured before and after hyperventilation using xenon-enhanced CT in 12 patients with acute brain lesions. RESULTS Five patients showed "paradoxical" reactivity (increased cerebral blood flow during hyperventilation) within the lesions. In five patients, hyperventilation induced ischemia in apparently normal regions of brain. In three patients, areas of luxury perfusion became ischemic during hyperventilation, while in three patients, lesions with moderate ischemia became more ischemic. Most patients showed more than one type of reactivity. CONCLUSIONS These findings document hyperventilation-induced ischemia in acute brain lesions, and demonstrate that this phenomenon affects both injured and apparently intact areas of the brain. Further studies are required to determine the clinical significance of these pathophysiologic changes.