Correlation of Continuous Electroencephalograms With Cerebral Blood Flow Measurements During Carotid Endarterectomy

During an 11-month period, 81 endarterectomies under a carefully controlled level of general anesthesia were monitored with continuous electroencephalograms (EEG) and intermittent regional cerebral blood flow (CBF) measurements. There was a high correlation between the CBF (milliliter per 100 gm per minute) during carotid occlusion and alterations in the EEG: no EEG change was seen with the flow above 30 ml/100 gm brain per minute, major changes were not seen with a flow between 18 and 30 ml, and changes invariably occurred with a flow below 17 ml. The degree of EEG change reflected the severity of flow reduction but was always reversible with the placement of a shunt. The EEG at the termination of the surgery corresponded with the patient's neurological state in that all EEG tracings were normal or unchanged as compared to the preoperative tracing and no neurological worsening occurred in any patients studied. The EEG is a valuable monitoring technique that indicates when a shunt is required and informs the surgeon of the state of cerebral function not only during occlusion but also throughout the entire operative procedure.