Abstract
We studied the reversibility of the cortical function after temporary occlusion during aneurysm surgery by monitoring the direct cortical response (DCR).
DCR changes were studied in 43 aneurysm patients. There were no changes in PaO2, PaCO2, body temperature, and blood pressure during monitoring. The threshold was 3±1.1 mA, the latency 21.3±5.1 msec, and the amplitude 627±425 μV. Maximal depression of the amplitude occurred within 8 minutes. The DCR did not change in common carotid artery (CCA) occlusion (16 cases). In bilateral anterior cerebral artery (bil. A1) occlusion (8 cases), middle cerebral artery (M1) occlusion (17 cases), internal carotid artery (ICA) occlusion (1 case) and ICA + A1+M1 occlusion (1 case), based on the reduction rate of the amplitude and how long reduction lasted, changes in the DCR could be classified into 5 groups. Group 1 (4 cases): The amplitude of DCR restored before declamping. Group 2 (7 cases): Reduction rate of less than 70%. Group 3 (9 cases): Reduction rate of more than 70% lasting up to 20 minutes. Group 4 (5 cases): Reduction rate of more than 70% lasting more than 20 minutes. Group 5 (2 cases): DCR disappeared for more than 30 minutes (one case of bil. A1 occlusion, one case of ICA+A1+M1 occlusion). When the reduction rate was less than 70%, or was more than 70% and lasted up to 20 minutes (Groups 1, 2 and 3), the amplitude of the DCR was restored completely. But, when the reduction rate greater than 70% and lasted for more than 20 minutes (Group 4), the amplitude of the DCR was not completely restored. When the DCR disappeared for more than 30 minutes, the amplitude of the DCR was never restored, and postoperative computed tomographic scan revealed low density (infarction) in the perfused area (Group 5). It is concluded that monitoring of the DCR is useful during temporary occlusion and when the reduction rate of the DCR amplitude is more than 70%, the safe critical time of ischemia is within 20 minutes.
