Determination of the Effective Dose of a Single Intravenous Dose of Tegileridine Fumarate for Postoperative Analgesia After Orthopedic Surgery: A Up-and-Down Sequential Allocation Study

The goal of this clinical trial is to determine the 90% effective dose (ED90) of a single intravenous injection of tegileridine fumarate for postoperative analgesia in adult patients aged 18-75 years with American Society of Anesthesiologists (ASA) physical status I-III undergoing orthopedic surgery, including spinal fusion surgery, femoral fracture fixation, and total knee arthroplasty. The main questions this study aims to answer are: What is the ED90 of a single intravenous dose of tegileridine fumarate for achieving adequate postoperative analgesia, defined as a Numeric Rating Scale (NRS) pain score ≤ 3 within 30 minutes after awakening from anesthesia without the need for rescue analgesia? Participants will: Receive a single intravenous injection of tegileridine fumarate during skin closure at the end of surgery. Start with an initial dose of 0.5 mg, with subsequent doses adjusted upward or downward in 0.1 mg increments for the next participant based on the analgesic response of the preceding participant, following a biased-coin up-and-down sequential dose allocation design. Be closely monitored during the postoperative recovery period for pain intensity, vital signs (including heart rate, blood pressure, respiratory rate, and oxygen saturation), and adverse reactions such as nausea, vomiting, respiratory depression, agitation, and other opioid-related side effects. This study aims to identify an optimal single-dose regimen of tegileridine fumarate that provides effective postoperative analgesia with an acceptable safety profile, thereby improving postoperative pain control and promoting enhanced recovery in patients undergoing orthopedic surgery.