Transcutaneous Auricular Vagus Nerve Stimulation for Preventing Acute Kidney Injury in Patients Undergoing Cardiac Surgery With Cardiopulmonary Bypass

Inclusion Criteria: * Age ≥18 years * Scheduled for elective cardiac surgery with cardiopulmonary bypass under general anesthesia * Baseline estimated glomerular filtration rate (eGFR) ≥60 mL/min/1.73 m² (CKD-EPI formula) * American Society of Anesthesiologists (ASA) physical status classification I-III * New York Heart Association (NYHA) functional classification I-III * Able to understand and cooperate with study procedures * Willing to participate and provide written informed consent. For participants unable to read or sign due to incapacity or illiteracy, consent may be obtained from a legally authorized representative or witnessed by an impartial third party as per ethical guidelines Exclusion Criteria: * Solitary kidney, history of kidney transplantation, pre-existing renal replacement therapy, or pre-existing acute kidney injury (KDIGO criteria) * Contraindications to transcutaneous auricular vagus nerve stimulation, including active infection, dermatitis, skin breakdown, or severe psoriasis in the bilateral auricular region; allergy to silicone, electrode gel, or device materials; uncontrolled arrhythmia, symptomatic bradycardia, sick sinus syndrome, second- or third-degree atrioventricular block, implanted pacemaker or defibrillator; carotid sinus hypersensitivity; uncontrolled epilepsy; or active peptic ulcer disease * Received vagus nerve stimulation, auricular acupuncture, or transcutaneous electrical nerve stimulation within 1 month prior to enrollment * Long-…