We design this randomized controlled trial to compare the safety and efficacy of Oxycodone and Sufentanil for postoperative patient-controlled analgesia in patients undergoing hip surgery, with a view to finding the optimal postoperative analgesic regime with fewer adverse reactions and promoting patients' rehabilitation.

Hip surgery is a common type of orthopedic surgery. The pathologies are complex, including chronic conditions such as femoral head necrosis, primary hip dysplasia, hip joint osteoarthritis and rheumatoid arthritis, as well as acute diseases such as femoral neck fractures and intertrochanteric fractures. The surgical treatment includes closed reduction and internal fixation, open reduction and internal fixation, hemiarthroplasty (femoral head replacement), and total hip arthroplasty, etc. The population of patients undergoing hip surgery has a high proportion of elderly (>65 years old), with multiple preoperative comorbidities, and significant postoperative pain. We must achieve the balance between the providing sufficient analgesia and minimizing associated adverse reactions perioperatively for such group of patients, therefore promoting patients' rehabilitation.

Sufentanil, a pure μ receptor agonist with active metabolite, is a long-acting strong opioid which has high analgesic efficacy. It is commonly used in anesthesia practice, not only for intraoperative analgesia, but also postoperative pain relief, i.e. a popular drug of choice used for Patient Control Intravenous Analgesia (PCIA). However, sufentanil is associated with high incidence of postoperative nausea and vomiting (PONV), respiratory depression and other adverse reactions, which could negatively affect the patient's analgesic satisfaction, and compromise the course of postoperative recovery. It is important to establish an effective and safe postoperative analgesic regime that can achieve the comparable analgesic efficacy with reduced incidence of adverse reactions. Oxycodone is a semi-synthetic opioid which is extracted from the thebaine, it activates both μ and κ opioid receptors. It has been reported to have good analgesic effect and lower incidence of adverse reactions such as PONV in comparison with Morphine, and could be a reasonable option for PCIA. As Oxycodone can agonize κ receptors and reduce visceral pain, most of the existing studies on Oxycodone are focused on laparoscopic cholecystectomy and other abdominal surgeries, with the average age of study patients is between 40 to 55 years old, and also lack of large sample studies.

Based on the abovementioned literatures, we propose the hypothesis that in hip surgery, compared with Sufentanil PCIA, the equipotency dose of Oxycodone PCIA can achieve the same postoperative analgesic efficacy and may also reduce the incidence of adverse reactions associated with opioids.

Inclusion criteria:

• Patients undergoing unilateral hip surgery, sign the "informed consent form".
• Age above 18 years old, with both genders.

Exclusion criteria:

• Pregnant or lactating women.
• Patient with history of drug abuse, including but not limited to opioids, amphetamines, ketamine, etc.
• Allergic to opioids or any other anesthetic agent.
• History or family history of malignant hyperthermia.
• Have history of nervous system diseases such as peripheral neuropathy, psychiatric mental illness, or postoperative delirium.
• Other conditions that the investigators consider unsuitable for participation in the study, such as Parkinson's disease, unable to communicate, or impairment of cognitive function etc.
• Participation in another trial in the past three months.