Clinical trials

The goal of this clinical trial is to learn if the administration of oxycodone for preventive analgesia works to reduce the chronification of acute postoperative pain in adult participants undergoing major abdominal surgery. The main question it aims to answer is: • Does administration of oxycodone before surgical incision reduce the occurrence of chronic pain or relieve the chronic pain symptoms 3 months after the operation? Researchers will compare oxycodone + parecoxib sodium to placebo + parecoxib sodium combinations to see if oxycodone works to reduce the chronification of acute postoperative pain. Participants will: * Take oxycodone + parecoxib sodium or placebo + parecoxib sodium combinations before the surgical incision * Cooperate with the follow-up staffs and complete some checkups or tests within 3 months after the operation.