Complicated intra-abdominal infection (cIAI) triggers dysregulated systemic inflammation and immune paralysis leading to high organ failure and death risk. Ulinastatin is a protease inhibitor with anti-inflammatory properties, but its dose-related effects on immune-inflammation of cIAI patients remain unclear. This single-center single-blinded three-arm randomized controlled pilot study enrolls adult cIAI patients (≥18 years, SOFA≥2) at Fujian Medical University Union Hospital. Eligible patients are randomized into low-dose ulinastatin, high-dose ulinastatin and normal saline placebo groups (1:1:1, 5 days intravenous treatment plus standard care), total planned enrollment 165 participants after 10% dropout adjustment. Primary endpoint is Day5 change of Systemic Immune-Inflammation Index (SII); secondary outcomes include serial inflammatory biomarkers, SOFA variation, organ dysfunction, hospitalization duration, 28-day mortality and safety profiles. This pilot aims to clarify ulinastatin's immune-modulating effect and inform future large RCT design.
Able to provide written informed consent voluntarily.
Age ≥ 18 years old, any gender.
Diagnosed with severe complicated intra-abdominal infection (cIAI) within 48 hours, consistent with the 2025 expert consensus for cIAI diagnosis. Diagnosis is confirmed by clinical symptoms (fever, abdominal pain, distension, etc.), abdominal imaging (CT/ultrasound/MRI), intraoperative findings, or positive pathogen culture of abdominal drainage fluid.
Baseline Sequential Organ Failure Assessment (SOFA) score ≥ 2 points.
Severe immune deficiency conditions, including AIDS, prior solid organ or bone marrow transplantation, HIV infection with CD4 count < 200 cells/mm³, long-term high-dose glucocorticoid therapy (prednisone > 20 mg/day), ongoing chemotherapy for malignant tumors, or absolute neutrophil count < 1000 cells/mm³.
Severe irreversible underlying diseases, including chronic renal failure requiring dialysis, Child-Pugh grade C liver disease, liver disease with severe portal hypertension, or acute liver failure.
Patients with active malignant tumors, pregnancy, or severe psychiatric disorders.
American Society of Anesthesiologists (ASA) physical status grade IV or above.