Middle cerebral artery circulation during carotid surgery

Objective-Perioperative carotid cross-clamping might induce low stump press ures as well as hypoperfusion of the middle cerebral artery. In this study blood flow velocities in the middle cerebral artery were compared with intr aoperative measurements of the poststenotic carotid blood pressure. Design-Forty-one patients with internal carotid artery stenosis were operat ed on without shunting, under general anesthesia. Poststenotic carotid pres sures and middle cerebral artery flow velocities were measured before and d uring cross-clamping. The hemodynamic responses to preoperative carotid com pressions and intraoperative cross-clamping were evaluated. Results-In seven patients the poststenotic carotid blood pressure decreased on clamping despite unchanged or even increased middle cerebral artery blo od flow velocities. In all other patients, pressure changes were significan tly correlated to the decrease in middle cerebral artery blood flow velocit ies. Autoregulatory blood flow velocity responses after preoperative common carotid artery compression were not reproducible by cross-clamping. Conclusions-Stump blood pressure measurements may nest reflect middle cereb ral artery perfusion in about 20% of thrombendarterectomies performed under general anesthesia. A possible explanation might be dimished cerebral auto regulation and changes in collateral flow distributions.