Is Transcranial Doppler Useful in the Detection of Internal Carotid Artery Cross-Clamp Intolerance?

The aim of this study was to test the hypothesis that a drop in the systolic blood flow velocity in the middle cerebral artery of 70% or more, measured by transcranial Doppler, is a better criteria in the detection of cross-clamp intolerance than electroencephalogram (EEG) and somatosensory evoked potential (SSEP) monitoring. After exclusion of patients with a recent stroke, urgent procedures and combined procedures, a transcranial Doppler with compression test was scheduled in 85 patients. In 13 patients the drop was 70% or more and in these patients a transcranial Doppler was also performed during the reconstruction of the internal carotid artery (the study group) under general anaesthesia. A shunt was used because of EEG and SSEP abnormality in one patient. No changes were observed in the remaining patients and no intraoperative strokes were seen. The transcranial Doppler monitoring was unreliable in three patients. During cross-clamp, the systolic blood flow velocity in the middle cerebral artery dropped less than 70% in four and 70% or more in six patients. It is concluded that using a drop of 70% or more of the systolic blood flow velocity in the middle cerebral artery during internal carotid artery cross-clamp, as an indicator of cross-clamp intolerance, will lead to unnecessary shunting.