The relative risk of shunting versus not shunting during carotid endarterectomy was analyzed retrospectively in 1935 cases undergoing carotid endarterectomy for carotid ulcerative stenosis. The need for shunting was based on a correlation between electroencephalographic changes and a fall in cerebral blood flow below the critical level required for adequate perfusion during the period of carotid occlusion. Patients were divided into four risk categories for surgery, based on medical and neurological risks and angiographic findings. Shunts were required in 30% of the low risk group and 56% of the high risk group. Based on the severity of reductions of cerebral blood flow during the period of carotid occlusion it is concluded that 12% of all patients would have sustained a major deficit, 15% a minor or transient deficit, and 20% a transient deficit without shunting. The risk of shunting 792 cases in this series was 0.5%. Overall minor morbidity, major morbidity, and mortality each approximated 1% in this series.
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