This is a prospective, triple-blind, placebo-controlled, single-center randomized clinical trial to evaluate the efficacy and safety of early oral lactulose for promoting postoperative gastrointestinal functional recovery in patients undergoing appendectomy for complicated appendicitis. Eligible patients aged ≥18 years with complicated appendicitis confirmed by preoperative SAS 2.0 score, intraoperative findings, or postoperative pathology will be randomly assigned 1:1 to receive oral lactulose or placebo on postoperative day 1 and day 2. The primary outcome is time to GI-2 (time from surgery to the later of first defecation or first tolerance of solid food). Secondary outcomes include time to first flatus, defecation rate within 72 hours, postoperative nausea and vomiting, length of hospital stay, medical costs, postoperative complications, and lactulose-related adverse events. A total of 150 patients will be enrolled. This study aims to provide high-level evidence for optimizing postoperative management in patients with complicated appendicitis.

Inclusion Criteria:

• 1.Age ≥18 years.2.Complicated appendicitis confirmed by SAS2.0 score, intraoperative findings, or pathology.3.Undergoing appendectomy (open or laparoscopic).4.Able to provide informed consent and comply with follow-up.

Exclusion Criteria:

• 1.Preoperative intestinal obstruction, IBD, or intestinal tumor.2.Planned postoperative fasting >48 hours.3.Hypersensitivity to lactulose or placebo.4.Severe organ dysfunction (ASA ≥IV).5.Pregnancy or lactation.6.Cognitive or psychiatric disorder impairing follow-up.