Objective: To construct a perioperative EEG database for elderly patients under general anesthesia and to explore the relationship between their EEG spectrum characteristics and the occurrence and severity of postoperative delirium. Content: This study aims to investigate elderly patients undergoing elective orthopedic surgery under general anesthesia with endotracheal intubation, analyze the changes in the perioperative EEG spectrum and its correlation with the occurrence of postoperative delirium, and explore the relationship between perioperative EEG changes and the occurrence of postoperative delirium. Methods: Patients aged 60 years or older who were scheduled to undergo orthopedic joint replacement or spinal surgery and had a hospital stay of more than 2 days were selected. All patients underwent MMSE and 3D-CAM assessment before surgery. Before anesthesia induction, anesthesia depth monitoring electrodes were placed on the patient's occipital or frontal temporal region, and EEGs were collected in awake and quiet states, under general anesthesia, and during anesthesia recovery. In the PACU, the score was calculated based on the CAM-ICU scale. The patients were assessed with the 3D-CAM scale for awakening once a day at 15:00-20:00 the day before surgery, and twice a day at 9:00-11:00 and 15:00-20:00 during 1-5 days after surgery, or at any time when obvious delirium symptoms appeared, unless discharged from the hospital or taking sedatives (RASS<-3). Ten minutes after the assessment, the occipital EEG was monitored when the patient was conscious and quiet, or when obvious delirium appeared. According to the test results of the 3D-CAM scale, it was determined whether the patient had postoperative delirium, and the patients were divided into the delirium group and the non-delirium group. The EEG characteristics of the two groups of patients were analyzed before, during, and after surgery. Research significance: The results of this study can provide objective indicators and theoretical basis for monitoring and diagnosing the occurrence and development of POD, which can help clinicians to identify patients with increased risk of delirium at an early stage, adjust the plan in time, and change the triggering risk factors of POD.

Preoperative cognitive and delirium assessment:

MMSE scale assesses the patient's preoperative cognitive function status: the total score is 30 points, the higher the score, the better the cognitive function. Considering the impact of education level on MMSE assessment, combined with my country's actual situation and previous studies, we set the assessment criteria for illiterate or most primary and junior high school education levels to ≤17, ≤20, and ≤24, respectively. Individuals below the corresponding standards are considered to have cognitive impairment before surgery.

Preoperative 3D-CAM baseline value for delirium assessment: patients were assessed for delirium using the 3-minute rapid mental confusion assessment method (3D-CAM) between 15:00 and 20:00 the day before surgery.

Postoperative delirium assessment:

During the postoperative PACU period, the score was calculated based on the CAM-ICU scale; 1-5 days after surgery, patients underwent 3D-CAM assessment twice a day at 9:00-11:00 and 15:00-20:00, or at any time when obvious delirium symptoms appeared, unless discharged or taking sedatives (RASS<-3).

Inclusion Criteria:

Patients aged ≥ 60 years, scheduled for orthopedic joint replacement or spinal surgery, ASA grade I-III, expected surgery time ≥ 2 hours, and able to provide written informed consent.

Exclusion Criteria:

1. Patients with central nervous system diseases or mental disorders;
2. patients with severe systemic diseases such as cardiopulmonary, liver and kidney dysfunction, coagulation dysfunction, etc.;
3. patients who frequently use psychotropic drugs, opioids or corticosteroids;
4. patients with a history of intraoperative awareness;
5. patients who are unable to complete preoperative delirium screening due to severe blindness, deafness, illiteracy or Mandarin speaking;
6. patients who are expected to undergo a second operation within 7 days.

Elderly patients undergoing elective orthopedic joint replacement or spinal surgery