The contribution of the external carotid artery to cerebral perfusion in carotid disease

Purpose: In the presence of carotid occlusion, the external carotid artery (ECA) becomes an important source of cerebral blood flow especially if the circle of Willis is incomplete. The contribution of the ECA to hemispheric blood flow in patients with severe ipsilateral carotid stenosis has never been previously investigated. Methods: One hundred eight patients were monitored during sequential cross-clamping of the external (ECA) and then ipsilateral internal carotid artery (ICA) during carotid endarterectomy using transcranial Doppler sonography (TCD) (Neuroguard CDS, Los Angeles, Calif), to measure middle cerebral artery blood flow velocity, and near-infrared spectroscopy, to measure regional cerebral oxygen saturation (CsO2) (Invos 3100A; Somanetics, Troy, Mich). Results: On the ipsilateral ECA cross-clamp, the median fall in CsO2 was 3% (interquartile range, 1%0-4%; P <.0001). On addition of the ICA cross-damp there was a further fall of 3% and a total fall of 6% (3%-9%; P <.0001). The median percentage fall in middle cerebral artery blood now velocity on ECA clamping was 12% (4Yo-24%; P <.0001); on ICA clamping it was 48% (25%-74%; P <.0001). Falls in TCD on ECA clamping were greater with increasing severity of ipsilateral ICA stenosis. The correlation between CsO2 and TCD on external clamping, although less strong than that on internal clamping, was statistically significant r = 0.32; P =.01; Spearman rank correlation). Conclusions: The falls in TCD and CsO2 were of a similar order of magnitude and must therefore reflect a fall in cerebral perfusion. The ipsilateral ECA contributes significantly to intracranial blood flow and oxygen saturation in severe carotid stenosis.