Transauricular Vagus Nerve Stimulation Frequencies for Postoperative Pain

The goal of this clinical trial is to learn whether different frequencies of transauricular vagus nerve stimulation (tVNS) can reduce postoperative pain and opioid consumption in adults undergoing abdominal or urologic surgery. It will also evaluate the effects of tVNS on recovery quality, autonomic function, and treatment safety. The main questions it aims to answer are: Does transauricular vagus nerve stimulation reduce postoperative opioid consumption during the first 24 hours after surgery? Do different stimulation frequencies (high-frequency and low-frequency tVNS) produce different effects on postoperative pain and autonomic responses? Is transauricular vagus nerve stimulation safe and well tolerated in surgical patients? Researchers will compare high-frequency tVNS, low-frequency tVNS, and sham stimulation (inactive stimulation) to determine their effects on postoperative pain and opioid requirements. Participants will: Be randomly assigned to receive high-frequency tVNS, low-frequency tVNS, or sham stimulation. Receive two 30-minute stimulation sessions, one before anesthesia and one after surgery in the post-anesthesia care unit. Undergo assessments of postoperative pain, opioid consumption, need for rescue analgesics, postoperative nausea and vomiting, heart rate changes, and quality of recovery. Be monitored for adverse events related to the intervention during the study period. A total of 174 participants will be enrolled in this single-center, randomized, double-blind, sham-controlled clinical trial.