This is a single-center, randomized, controlled, double-blind clinical trial. A total of 148 patients undergoing elective open upper abdominal surgery will be included and randomly assigned 1:1 to receive ultrasound-guided erector spinae plane block with liposome bupivacaine plus bupivacaine hydrochloride or bupivacaine hydrochloride alone. The primary outcome is the AUC of resting pain scores from 0 to 72 hours postoperatively. This study aims to evaluate the analgesic efficacy and safety of liposome bupivacaine and provide a long-acting and safe postoperative analgesia strategy.

Inclusion Criteria:

1. Patients scheduled for elective open upper abdominal surgery, including open liver, gastric and pancreatic surgery.
2. Patients receiving general anesthesia with tracheal intubation.
3. Aged from 18 to 80 years old.
4. Patients with American Society of Anesthesiologists (ASA) physical status class Ⅰ-Ⅲ.
5. Patients who can understand the trial content, are willing to strictly follow the clinical research protocol and complete the trial, and voluntarily sign the informed consent form.

Exclusion Criteria:

1. Pregnant or lactating women.
2. Patients complicated with severe primary diseases of the lung, liver, kidney, cardiovascular system and hematopoietic system.
3. Bleeding tendency or coagulation dysfunction, defined as international normalized ratio (INR) ≥ 1.4, activated partial thromboplastin time > 38 s, or platelet count < 80×10⁹/L.
4. Patients with aggravated cardiac diseases (complex congenital heart disease, heart failure and valvular disease) or pulmonary insufficiency.
5. Skin infection at the puncture site for erector spinae plane block (ESPB).
6. Previous history of neurological or psychiatric diseases, with inability to read, understand and communicate.
7. Current obstructive or restrictive pulmonary disease.
8. Patients with BMI greater than 30 kg/m².
9. Drug abuse, long-term regular use of analgesics, or allergy to the study drugs.
10. Patients who refuse to provide informed consent.
11. Those enrolled in other randomized controlled trials simultaneously or with other conditions unsuitable for participation in this trial.