The effect of transcutaneous auricular vagus nerve stimulation on postoperative delirium in elderly patients undergoing lower extremity orthopedic surgery

INTERVENTION: The transcutaneous auricular vagus nerve stimulation group (taVNS) group:Place the stimulating electrode on the concha subvessel and another ear clip to the earlobe.;Control group:Two electrode clamps attached to the earlobe and the heli Xrespectively ; CONDITION: Postoperative delirium PRIMARY OUTCOME: The incidence of postoperative delirium; SECONDARY OUTCOME: Gut microbiota;Neutrophil extracellular trap biomarkers;Postoperative gastrointestinal function indicators; INCLUSION CRITERIA: 1.Patients aged >= 60; 2. ASA grade II or III; 3. Scheduled for elective lower extremity orthopedic surgery.