Anrikefon-based Patient-controlled Intravenous Analgesia Following Laparoscopic Surgery

Inclusion Criteria: 1. Aged \>= 18 years but \< 75 years; 2. Scheduled to undergo elective laparoscopic colorectal surgery with an expected duration of \>=1 hour; 3. The incisional pain can be covered by the transversus abdominis plane block or rectus sheath block; yet patients still require postoperative patient-controlled intravenous analgesia. Exclusion Criteria: 1. Presence of preoperative cognitive impairment (Mini-Mental State Examination \[MMSE\] score \< 27), or inability to communicate due to language barrier; 2. Body mass index (BMI) \> 30 kg/m² or \< 18 kg/m²; 3. Presence of poorly controlled or untreated comorbidities, including but not limited to the following: hypertension characterized by a resting systolic blood pressure (SBP) \> 180 mmHg and/or diastolic blood pressure (DBP) \> 110 mmHg, coronary artery disease with unstable angina or myocardial infarction within 6 months, heart failure rated as New York Heart Association classification \>= III, severe chronic obstructive pulmonary disease (or in a state of acute exacerbation), severe hepatic insufficiency (Child-Pugh grade C), severe renal insufficiency (estimated glomerular filtration rate \< 30 ml/min/1.73m²), or American Society of Anesthesiologists (ASA) physical status classification \>= IV; 4. Continuous use of opioid analgesics for more than 10 days for any reason, or alcohol abuse (average daily intake of pure alcohol \> 36 g) within 3 months before screening; 5. Preoperative use of opioid or non-opioid analgesics with the interval between the last administration and randomization shorter than five half-lives of the drug or the duration of drug action (whichever is longer); 6. Known allergies or contraindications to opiates or other medications that may be used in this study, such as anesthetics, antiemetics, and nonsteroidal anti-inflammatory drugs (NSAIDs); 7. Anticipated need for postoperative mechanical ventilation； 8. Other conditions that are considered unsuitable for study participation.