The use of stable xenon-enhanced computed tomographic studies of cerebral blood flow to define changes in cerebral carbon dioxide vasoresponsivity caused by a severe head injury

Previous studies using the xenon-133 cerebral blood flow (CBF) method have documented the impairment of CO₂ vasoresponsivity after a severe head injury, but only global values can be obtained reliably with this technique. We studied CO₂ vasoresponsivity using the stable xenon-enhanced computed tomographic CBF method, which provided information about well-defined cortical regions and deep brain structures not available with the xenon-133 method. In 17 patients with admission Glasgow Coma Scale scores of 8 or less, hemispheric CO₂ vasoresponsivity ranged from 1.3 to 8.5% per mm Hg change in partial CO₂ pressure. Lobar, cerebellar, basal ganglia, and brain stem CO₂ vasoresponsivity frequently varied from the mean global value by more than 25%. In all but one patient, local CO₂ vasoresponsivity in one or more of these areas differed from the mean global value by more than 50%. The greatest variability occurred in patients with acute subdural hematomas and diffuse (bihemispheric) injuries. This variability in CO₂ vasoresponsivity has important implications for the effective and safe management of intracranial hypertension that frequently accompanies severe head injury.