In view of the increasingly severe aging situation in China, the perioperative brain health of elderly patients has received increasing attention. Postoperative delirium (POD) is a common postoperative complication characterized by acute consciousness and cognitive dysfunction. The incidence of POD in elderly patients undergoing elective non cardiac surgery is 20%\ 45%, which often indicates poor cognitive recovery and becomes a heavy burden for family and society. Although the weight of human brain only accounts for 2% of body weight, the oxygen consumption accounts for 20% of the total oxygen consumption of the whole body. On July 2, 2022, the British Journal of Anaesthesia (Chinese Academy of Sciences Division 1, Anesthesiology Division 1, IF11.719), the top international Journal in the field of anesthesiology, published the scientific research achievements of the first author of the applicant. It was found for the first time that sevoflurane, the most commonly used inhalation anesthetic in clinical practice, can cause the activation of glycolysis and the increase of lactic acid in the brain of elderly non-human primate marmosets, which suggests that general anesthetics will affect brain metabolism in the perioperative period. Therefore, we hypothesized that perioperative changes in brain metabolism might be related to the occurrence of POD in elderly patients. The purpose of this study was to study the relationship between the changes of brain metabolites and POD during perioperative period by noninvasive monitoring of the characteristics of brain tissue metabolites 24 hours before and 24 hours after the operation with hydrogen ion proton magnetic resonance spectroscopy (1-HMRS). In order to complete this purpose, this study plans to collect subjects aged 65\ 90 years who are scheduled to undergo oral and maxillofacial surgery under general anesthesia. The changes of brain metabolites before and after operation were collected by 1-HMRS, and the postoperative delirium related scale was evaluated to analyze the relationship between perioperative changes of brain metabolites and POD.