FMT for Feeding Intolerance Due to Gastrointestinal Dysfunction in Critically Ill Patients (FMT-FIT)

Inclusion Criteria:

1. Aged 18 to 70 years inclusive, regardless of ethnicity or gender;
2. Female participants are either non-fertile (i.e., physiologically incapable of pregnancy, including women with ≥2 years of menopause) or have no pregnancy plans;
3. Have been admitted to the ICU for ≥24 hours;
4. Expected ICU stay ≥7 days after study enrollment;
5. Screened positive for ≥1 manifestation of gastrointestinal dysfunction (intra-abdominal hypertension [IAH], massive gastric retention, diarrhea, lower gastrointestinal paralysis, bowel dilatation); enteral nutrition is then implemented under the guidance of the enteral feeding intolerance (FI) score, and participants with persistent FI after a 3-day trial are formally enrolled;
6. Participants can actively cooperate or passively complete relevant examinations and follow-up procedures;
7. Have signed a written informed consent form.

Exclusion Criteria:

1. Severe systemic infection in the early resuscitation phase, with hemodynamic instability, insufficient tissue perfusion, or severe fluid-electrolyte and acid-base imbalances;
2. Patients assessed by clinicians as having a high risk of death within 5 days, or those with restricted treatment decisions;
3. Active gastrointestinal bleeding, perforation, or other conditions with severe intestinal barrier impairment;
4. Patients unable to tolerate enteral nutrition meeting 50% of caloric requirements due to severe diarrhea, significant fibrotic intestinal stenosis, massive gastrointestinal bleeding, or high-output enterocutaneous fistula;
5. Planned or recent abdominal surgery (within 14 days prior to enrollment);
6. Current diagnosis of fulminant colitis or toxic megacolon;
7. Neutropenia (neutrophil count < 1500 cells/µL);
8. Patients with congenital or acquired immunodeficiency disorders;
9. Recent receipt of high-risk immunosuppressive or cytotoxic agents, e.g., rituximab, doxorubicin, or medium-to-high-dose corticosteroids (≥ 20 mg/day prednisone equivalent) for a duration of > 4 weeks;
10. Pregnant or lactating women;
11. Participation in another clinical trial as a subject at the time of enrollment or within 3 months prior to enrollment;
12. Doubtful validity of informed consent: subjects with mental illness, intellectual disability, poor motivation, or other factors that restrict the validity of informed consent for participation in this study.