Decreased transcranial Doppler carbon dioxide reactivity is associated with disordered cerebral metabolism in patients with internal carotid artery stenosis

Abstract

Purpose: The hemodynamic effect of stenosis of the internal carotid artery (ICA) can be assessed by measuring, with transcranial Doppler (TCD), the carbon dioxide (CO 2 ) reactivity of the cerebral vessels. The aim of this study was to determine whether a decreased CO 2 reactivity is associated with a compromised cerebral metabolism, as evaluated with 1H magnetic resonance spectroscopy (MRS). Methods: Sixty-six patients with unilateral or bilateral stenosis of the ICA, who were scheduled for carotid endarterectomy (CEA) and who had undergone both a TCD CO 2 reactivity test and a MRS examination, were included in this study. The ICA stenosis on one side (CEA side) was always more than 70%, and the extent of the stenosis on the contralateral side varied. Results: The CO 2 reactivity and the N-acetyl aspartate (NAA)/choline ratio were correlated in both hemispheres (r = .43; P < .001). Patients with an ICA occlusion contralateral to the CEA side are especially at risk for disordered cerebral hemodynamics and metabolism; in the contralateral hemisphere, the mean CO 2 reactivity and NAA/choline ratio were abnormal (18% and 1.52, respectively), and lactate was present in 85% of the patients. Changes indicative of disordered hemodynamics were found more often in symptomatic than in asymptomatic patients. Conclusion: A decreased CO 2 reactivity appears to be associated with a disordered cerebral metabolism. Patients with severe bilateral ICA stenosis are at risk for disordered cerebral metabolism and hemodynamics. Therefore, the indication for CEA based on the degree of ICA stenosis and clinical grounds might be refined with an additional test, such as the TCD CO 2 reactivity test. (J Vasc Surg 1999;30:252-60.)