The incidence of postoperative delirium was determined according to the Confusion Assessment Method (CAM) diagnostic algorithm. The algorithm consists of four clinical criteria: (1) acute onset and fluctuating course, (2) inattention, (3) disorganized thinking, and (4) altered level of consciousness. To define a patient as having delirium, both the first and the second criteria have to be present, as well as either the third or the fourth criteria. The CAM-ICU will be used for patients who are intubated in the postoperative period.

Electroencephalogram data were acquired using a 32-channel electroencephalogram recording system (Brain Products, Germany). A 5 min, baseline, eyes-closed recording was conducted at the preoperative holding room when the patient was at rest. Recording of electroencephalogram was commenced before the start of anesthetic induction and was stopped before discharge of the patient from the operating room. We defied delta (1 to 3 Hz), theta (4 to 7 Hz), alpha (8 to 12 Hz), and beta (13 to 40 Hz) frequency bands. And then, the relative power of each frequency bands to the total power of the sum is calculated.

Identify biomarkers (such as Ubiquitin carboxyl-terminal hydrolase L1 (UCH-L1), brain-derived neurotrophic factor (BDNF), and metalloproteases-9 (MMP-9) )of delirium and neural damage through changes in circulating plasma proteins and molecules