The goal of this observational study is to evaluate whether intraoperative dexmedetomidine use is associated with postoperative delirium in adults undergoing cardiac surgery. The study includes two linked components. First, researchers will analyze routinely collected clinical data from patients who underwent cardiac surgery at Tongji Hospital between January 2015 and December 2025. Second, archived plasma samples from a previously established observational cohort will be tested for matrix metalloproteinase-8 (MMP-8), a blood protein involved in inflammation and tissue injury. Researchers will compare patients who received dexmedetomidine during surgery with patients who did not receive dexmedetomidine. The decision to administer dexmedetomidine was made by the attending anesthesiologist based on the patient's clinical condition and routine anesthetic practice and was not assigned by the study protocol. The study will examine the associations among intraoperative dexmedetomidine use, perioperative changes in MMP-8, and postoperative delirium.