TRANSCRANIAL DOPPLER FOR DETECTION OF CEREBRAL-ISCHEMIA DURING CAROTID ENDARTERECTOMY

We evaluated transcranial Doppler sonography (TCD) for the detection of cerebral ischaemia during carotid endarterectomy in 30 male and 14 female patients with ipsilateral focal cerebro-vascular symptoms. Surgery was performed during halothane-nitrous oxide anaesthesia with moderate hypocapnia. Eight patients had a temporary shunt owing to contralateral occlusion or a stump pressure below 40 mmHg, and/or EEG flattening. Transcranial Doppler sonography was followed intra-operatively together with electro-encephalography (EEG), internal carotid artery (ICA) pressures and cerebral blood flow (CBF). Middle cerebral artery mean flow velocity (V(mean)) was 38 (22-96) cm s-1 (median and range) and decreased during cross-clamping to 28 (10-60) cm s-1 (p < 0.0001). After removal of the clamp it increased to 42 (20-102) cm s-1 (p < 0.0001). A V(mean) clamp of less than 30 cm s-1 together with a V(mean) clamp:V(mean) pre-clamp ratio of less than 0.6 showed an accuracy with respect to CBF below 20 ml 100 g-1 min-1 of 89%. A V(mean) clamp:V(mean) pre-clamp ratio below 0.4 detected all patients with EEG flattening (n = 3) (accuracy 97%). The corresponding level of accuracy obtained with stump pressure was 80%. The results indicate that middle cerebral flow velocity enables an increase in the accuracy of detecting cerebral ischaemia during carotid endarterectomy.