Postoperative delirium (POD) is a common perioperative complication, which can lead to adverse outcomes. Patients undergoing carotid endarterectomy (CEA) were elderly, complicated with vascular risk factors, cognitive dysfunction, some also had a history of stroke, and the circulation fluctuated greatly during the operation, often resulting in hypoperfusion of cerebral tissue and hypoxia. Therefore, they're the high-risk group of POD. Near-infrared Spectroscopy (NIRS) can continuously and noninvasively monitor local cerebral oxygen saturation (SctO2) to identify the mismatch of oxygen supply and demand in brain tissue. However, for CEA patients, the association between intraoperative SctO2 changes and POD remains unclear. This study intends to explore the association between them and determine the SctO2 threshold for predicting POD. We will monitor SctO2 intraoperatively, follow up and collect data postoperatively.