Application of simultaneous monitoring of cortical EEG and scalp EEG during anterior circulation aneurysm surgery

Objective To develop a simple and effective method for monitoring cortical ischemia after temporary occlusion of the parent arteries during anterior circulation intracranial aneurysm surgery. Methods Fifty-two patients with anterior circulation aneurysm （58 aneurysms） received craniotomy from April to November 2008, and at the same time, cortical electroencephalography （EEG） and scalp EEG were monitored during the surgery. According to the international 10/20 electrode placement system, scalp electrodes were placed on O1, O2, P3, P4, T5, and T6 for monitoring the changes in the depth of anesthesia. A cortical strip electrode was placed on the cortical surface supplied by the artery that was possibly blocked during the operation, which was used to monitor the possible cortical ischemia. For patients who had cortical EEG suppression after the temporary occlusion of the parent arteries were compared with the changes of scalp EEG. Whether there were ischemic events in the corresponding supply territory after vascular occlusion were observed after surgery. Results Of the 58 aneurysms, 40 aneurysms and 41 major arteries were occluded temporarily. After being occluded temporarily in 19 arteries of 18 patients, cortical EEG changed significantly, while scalp EEG did not change significantly. Only 9 patients had ischemic events in the corresponding supply territories after the occlusion in the cortical EEG significant change group. The changes in the depth of anesthesia had the consistent impact on cortical and scalp EEG. Conclusions Simultaneous monitoring of cortical and scalp EEG is a simple and effective method for monitoring cortical ischemia during anterior circulation intracranial aneurysm surgery, and may effectively identify the effect of anesthesia on EEG. Key words: electroencephalography;  intracranial aneurysm;  anesthesia;  monitoring, intraoperative