Transauricular Vagus Nerve Stimulation Frequencies for Postoperative Pain

Postoperative pain remains a major challenge in perioperative care and is associated with delayed recovery, increased healthcare utilization, and greater opioid consumption. Despite advances in multimodal analgesia, opioid medications continue to play a central role in postoperative pain management and may be associated with adverse effects such as nausea, vomiting, respiratory depression, and prolonged recovery. Therefore, the development of effective non-pharmacological adjunctive strategies is of considerable clinical interest.

Transauricular vagus nerve stimulation (tVNS) is a non-invasive neuromodulation technique that stimulates the auricular branch of the vagus nerve through the external ear. Experimental and clinical studies suggest that vagal stimulation may modulate pain perception through activation of central autonomic pathways, enhancement of descending inhibitory pain mechanisms, and regulation of inflammatory responses. Previous clinical trials have demonstrated promising effects of tVNS on acute and chronic pain conditions, including reductions in postoperative pain scores.

However, the optimal stimulation parameters for perioperative analgesia remain uncertain. In particular, the influence of stimulation frequency on clinical outcomes and autonomic responses has not been adequately investigated. Different stimulation frequencies may activate distinct neural pathways and produce different effects on pain modulation and autonomic regulation.

This study is designed to evaluate the effects of different frequencies of transauricular vagus nerve stimulation applied before and after surgery in adult patients undergoing elective surgical procedures. In addition to assessing postoperative opioid requirements, the study will explore the relationship between autonomic responses and postoperative recovery. The findings may contribute to the optimization of non-pharmacological analgesic strategies and support the incorporation of transauricular vagus nerve stimulation into multimodal perioperative pain management protocols.

Inclusion criteria

• Adults aged 18 to 59 years.
• Undergoing elective abdominal or urologic surgery.
• American Society of Anesthesiologists (ASA) physical status I-III.
• Able and willing to provide written informed consent.

Exclusion criteria

• History of neurological disorders.
• History of psychiatric disorders.
• Inability to understand study procedures.
• Pregnancy.
• Cognitive impairment.
• Communication difficulties that interfere with study assessments.
• Auricular dermatitis or skin lesions at the stimulation site.
• Pre-existing cardiac arrhythmia.
• Chronic opioid use.
• Implanted electronic medical devices, including pacemakers.