The goal of this pilot study is to test the hypothesis that liposomal bupivacaine extends the duration of paravertebral block in patients undergoing radical nephrectomy, achieving improved analgesia compared to conventional bupivacaine. The main questions it aims to answer are:

• Area under curve of numeric rating scale of pain from 12 to 72 h after surgery.
• Cumulative opioid consumption during the period of 12 to 72 h after surgery.

Random numbers will be generated by an independent biostatistician in a 1:1 ratio, sealed in sequentially numbered opaque envelopes, and stored by a study coordinator. Only anesthesiologists who perform paravertebral block know group allocation but are not involved in other parts of the trial. Patients, other health-care team members, and investigators for data collection and outcome assessment are masked from group assignments.

Paravertebral block will be performed with either liposomal bupivacaine or plain bupivacaine. The efficacy of nerve block will be assessed every 5 minutes after local anesthetic injection. We will evaluate pain severity, opioid consumption, and occurrence of adverse events at the following timepoints, i.e., end of surgery, 30 minutes after surgery, and 2, 6, 12, 24, 36, 48, 60, and 72 hours after surgery. Additionally, occurrence of complications, quality of recovery, and subjective sleep quality will be assessed during hospital stay after surgery.

Inclusion Criteria:

• Age between 18 and 70 years old.
• Scheduled for laparoscopic-assisted unilateral radical nephrectomy.
• Agree to undergo regional nerve blockade and receive patient-controlled intravenous analgesia after surgery.

Exclusion Criteria:

• Renal cancer with venous thrombus of grade II or higher, or cases that may convert to open surgery.
• Body mass index ≥30 kg/m² or ≤15 kg/m².
• Severe renal dysfunction (serum creatinine >442 μmol/L or requiring renal replacement therapy), severe liver dysfunction (Child-Pugh class C), or American Society of Anesthesiologists class ≥IV.
• Contraindications for deep nerve block, including severe spinal deformity or history of spinal surgery, severe coagulation abnormalities (international normalized ratio >1.7, activated partial thromboplastin time >4 seconds above normal, platelet count <80×10⁹/L), trauma or infection at the planned puncture site, or severe lumbar back pain.
• Chronic opioid dependence and long-term use of various analgesics for more than 3 months.
• Preoperative inability to communicate due to severe dementia, language barriers, or end-stage diseases.
• Preoperative concomitant central nervous system and/or peripheral nervous system diseases.
• Planned endotracheal intubation and admission to the intensive care unit after surgery.
• Known allergy to local anesthetics.
• Other conditions that are deemed unsuitable for trial participation by the attending surgeons or investigators.