Cerebral blood flow, internal carotid artery pressure, and the EEG as a guide to the safety of carotid ligation.

Twenty patients with aneurysms of the internal carotid artery underwent temporary clamping, in turn, of the internal and then the common carotid artery. Cerebral blood flow, internal carotid artery pressure, and the EEG were recorded to assess the probability of cerebral ischaemia after permanent ligation. With this method of monitoring the cerebral circulation, 17 of the 20 patients had a permanent carotid ligation without neurological deficit; in the other three ligation was contraindicated. Although a correlation was observed between the reduction of cerebral blood flow and the fall in internal carotid artery pressure caused by temporary clamping (P<0·01), the scatter of data was too wide to predict cerebral blood flow from the change in carotid artery pressure. Similarly, EEG slowing was usually associated with low cerebral blood flow but exceptions occurred. Ligation was safe when, during temporary clamping, cerebral blood flow exceeded 40 ml/100 g/min, but was deemed unsafe when flow was less than 20 ml/100 g/min. In the range 20-40 ml/100 g/min, consideration of the internal carotid artery pressure permitted more patients to be safely ligated than if the decision had rested on changes in cerebral blood flow alone.