Figure 2. Preoperative carbon dioxide reactivity compared to intraoperative TCD results with cases presenting critical SEP changes marked (X). TCD changes were defined critical in case of post/preclamping Vm-MCA ratio less or equal to 0.4 (broken vertical line). Carbon dioxide reactivity cut-off point (1.5%/mmHg) is indicated by the horizontal broken line. Eleven patients were excluded because of preoperative carbon dioxide testing results (n = 7), missing TCD data postclamping (n = 2), technical defect of the SEP machine (n = 1), and critical SEP changes before ICA clamping (n = 1).