Carbon dioxide reactivity in the evaluation of cerebral ischemia.

Carbon dioxide reactivity, as measured by transcranial Doppler, has been determined in a group of patients with carotid artery disease and compared to a control group. CO2 reactivity was readily evaluated using transcranial Doppler by having the patients breathe 5% CO2 via a rebreathing circuit. There were significant differences (P less than 0.01) between the symptomatic patients and asymptomatic controls, as well as between symptomatic and asymptomatic hemispheres (P less than 0.05) in the patients with carotid artery disease. Five patients had revascularization procedures with all showing improved CO2 reactivity in the symptomatic and asymptomatic hemispheres. The improvement occurred early in patients after carotid endarterectomy. Two patients demonstrated improved reactivity at 6 to 13 months after extracranial-to-intracranial bypass. Transcranial Doppler has proven to be an easily performed and repeatable method of evaluating CO2 reactivity and its response to treatment.