Effects of transcutaneous auricular vagus nerve stimulation on postoperative delirium induced by tourniquet application in elderly patients undergoing lower extremity surgery

INTERVENTION: taVNS intervention group: The observation group used the vagus nerve stimulator and the disposable stimulation electrode was attached to the distribution area of the auricular branch of the vagus nerve in the left auricle (the posterior 1/3 of the concha cavity); the stimulation parameters were: continuous wave, frequency 20 Hz, pulse width 200 µs, initial current intensity 2 mA, adjusted gradually to 5 8 mA and maintained with the standard of "the patient feels slight tingling and numbness without obvious discomfort". Intervention time: 1. The first day before surgery: a single intervention was performed in the ward for 30 min; 2.The operation day: the intervention was started 30 minutes before anesthesia induction and continued until 30 minutes after tourniquet deflation after the end of surgery, and the intraoperative stimulation intensity was maintained at 80% of the preoperative tolerance intensity (to avoid excessive intensity due to the patient's insensitivity to stimulation under anesthesia); 3.The first day after surgery: a single intervention was performed in the ward for 30 min with the same current intensity as the first day before surgery.;Control group:The control group wore the same stimulation electrodes and equipment as the observation group, with the same electrode placement position and intervention duration as the observation group; after the patient reported feeling slight tingling and numbness, the device current output was turned off immediately, without effective electrical stimulation throughout the process, and only the device was kept on to ensure the effectiveness of blinding.; CONDITION: postoperative delirium PRIMARY OUTCOME: Occurrence of postoperative delirium (POD);Perioperative and rehabilitation indicators; SECONDARY OUTCOME: Cognitive function;Serological indicators; INCLUSION CRITERIA: 1. Age >= 65 years, any gender; 2. Scheduled for lower limb orthopedic surgery, with planned use of a tourniquet during surgery; 3. American Society of Anesthesiologists (ASA) classification I–III; 4. Basic normal cognitive function before surgery, MoCA score >= 26, MMSE score >= 24; 5. Patient or their legal representative is fully informed and has signed written informed consent.