Thi investigators aims to observe the impact of perioperative body temperature and the noise of operating room on postoperative delirium for elderly patients undergoing abdominal surgery. And based on this study the investigators aimed to explore the potential risk factors of postoperative delirium for elderly patients undergoing abdominal surgery.

Inclusion Criteria:

• Age 65-90 years old;
• ASA I-III;
• Patients who plan to undergo elective abdominal surgery under general anesthesia;
• Volunteer to participate in this study and sign informed consent.

Exclusion Criteria:

• Patients with known mental illness or lack of communication or cognitive impairment before operation;
• Severe vision, hearing, language impairment or other reasons unable to communicate with visitors;
• Severe dysfunction of important organs such as heart, brain, lung, liver, kidney, etc.;
• Long-term use of sedatives, antidepressants or alcoholism;
• Patients with severe postoperative complications and admitted to intensive care unit;
• Patients who refused or failed to complete the cognitive function test.
• Patients who could not cooperate with the study for any other reason.

Elderly patients who underwent abdominal surgery under general anesthesia.