Delayed carotid shunt occlusion detected by electroencephalographic monitoring

Little has been recorded in the anesthesia literature concerning the changes in the electroencephalogram (EEG) that may occur during carotid endarterectomy many minutes after shunt placement and restoration of flow and that may be attributed to "delayed" shunt occlusion or cerebral emboli. We describe a patient in whom EEG changes indicative of cerebral ischemia occurred at the time of carotid clamping. The changes resolved promptly after placement of a carotid shunt but recurred 11 minutes later. Because of the EEG changes, the carotid shunt was evaluated and found to have become occluded. EEG monitoring was crucial to the detection of shunt occlusion in the absence of other systemic changes or surgical difficulties. The rapidity and magnitude of the changes in the EEG suggest that, if the occlusion had not been discovered and the patency of the shunt restored, the patient would have been at increased risk for neurologic injury.