Transcutaneous auricular vagus nerve stimulation (taVNS) is a novel non-invasive neuromodulation technique. Existing evidence suggested that taVNS improves pain management, sleep quality, inflammatory responses, and gastrointestinal recovery after surgery. This study is designed to test the hypothesis that perioperative use of taVNS may improve quality of recovery in patients after major noncardiac surgery.

The evolution of quality improvement initiatives, such as Enhanced Recovery After Surgery (ERAS) protocols, has shifted perioperative management paradigms toward prioritizing patient-centered subjective experiences such as quality of recovery over traditional outcomes such as mortality, morbidity, or physiological parameter recovery. Poor quality of recovery after surgery not only diminishes patient satisfaction but also correlates with increased 30-day postoperative complications, prolonged hospital stays, and elevated medical expenses.

The vagus nerve is a major component of the parasympathetic nervous system and is a critical relay for neuro-metabolic signals between the abdominal viscera and the brain. The ear is the only area where the vagus nerve is distributed on the body surface, and the auricular branch of the vagus nerve can project to nerve centers such as nucleus of solitary tract in the brainstem and the nucleus coeruleus in the midbrain.

Transcutaneous auricular vagus nerve stimulation (taVNS) can stimulate the auricular branch of the vagus nerve through surface electrodes located in the cymba conchae, and thus activate the vagus nerve circuit, regulate the activity of the brainstem, thalamus, and other brain regions, and regulate the related peripheral organs. Available evidences showed that taVNS reduces inflammatory response to surgery through cholinergic anti-inflammatory pathways, improves analgesia by reducing inflammation and activating serotonin and endorphins analgesic pathways, and promotes gastrointestinal function by regulating peristalsis and secretion of the digestive system; it was also found effective in improving sleep quality and relieving anxiolytic and depressive symptoms. The use of taVNS is relative safe; the incidence of adverse event is low and mainly included transient earache, headache, and local tingling, with no causal association to serious adverse events.

The investigators hypothesize that the application of taVNS in patients undergoing major noncardiac surgery may improve early postoperative quality of recovery.

Inclusion Criteria:

1. Aged ≥18 years but <85 years.
2. Scheduled for elective or limited-time noncardiac surgery with expected duration ≥2 hours.

Exclusion Criteria:

1. Lesions or infections of the auricle skin.
2. Recent or long-term use of cholinergic or anticholinergic medications.
3. Neurosurgery.
4. Expected mechanical ventilation with intubation for ≥1 day after surgery.
5. Diagnosed schizophrenia, epilepsy, Parkinson's disease, or myasthenia gravis before surgery.
6. Preoperative left ventricular ejection fraction (LVEF) <30%, or those with sick sinus syndrome, sinus bradycardia (heart rate <50 beats per minute), atrioventricular block of grade II or above, or implanted pacemaker.
7. Inability to communicate due to coma, severe dementia, or language barrier before surgery, or unable to cooperate with intervention.
8. American Society of Anesthesiologists physical status grade >IV, or estimated survival <24 hours.