Identification of Hemodynamic Patients for EC-IC Bypass Surgery

Abstract

Recurrent ischemic symptoms from a hemisphere where the internal carotid artery (ICA) is occluded are either embolic or hemodynamic. Distinguishing between these two etiologies is not possible on clinical grounds alone, although multiple, brief attacks including limb shaking are suggestive of hemodynamic origin (Levine et al. 1989). In particular, when the symptoms occur in relation to orthostatic changes, a clinical suspicion of an inadequate regional flow arises. Nevertheless, in most of these patients the setting of clinical symptoms alone and even when supplemented by angiography and CT will not identify the hemodynamic cases, and additional studies are needed. Measurement of CBF during CO₂ inhalation (Levine et al. 1989; Norrving et al. 1982) or after intravenous administration of acetazolamide (Vorstrup et al. 1986) has been used to evaluate the cerebral vasodilatory capacity. The development of positron emission tomography has permitted concomitant measurement of CBF, oxygen extraction fraction, and cerebral metabolism for oxygen (CMRO₂), which identifies critically perfused areas during baseline conditions. In addition, measurement of CBF and cerebral blood volume (CB) can be applied for this purpose (Gibbs et al. 1984).