Critically ill patients admitted to the intensive care unit (ICU) frequently present with gastrointestinal dysfunction and are at elevated risk of malnutrition. Gastrointestinal dysfunction is correlated with adverse clinical outcomes, including prolonged mechanical ventilation duration, extended ICU length of stay, and increased 90-day mortality.

In critically ill ICU patients, severe gut microbiota dysbiosis and intestinal barrier impairment may occur due to the burden of primary critical illnesses, as well as the administration of proton pump inhibitors and antibiotics. This cascade contributes to a high prevalence of gastrointestinal dysfunction, alongside profound gut-derived systemic inflammatory responses and organ damage. Given the pivotal role of gut microbiota in maintaining intestinal homeostasis, fecal microbiota transplantation (FMT) holds promise as a novel therapeutic strategy for enteral feeding intolerance secondary to gastrointestinal dysfunction in critically ill ICU patients.

This study intends to deliver FMT via a nasojejunal tube to critically ill patients with gastrointestinal dysfunction admitted to the ICU. Its objectives are to evaluate the intervention's effects on gastrointestinal function recovery and the alleviation of enteral feeding intolerance, while also assessing its impacts on intestinal barrier function, gut microbiota composition and metabolic profiles, serum metabolite signatures, immune-inflammatory responses (including lymphocyte subsets, cytokines, C-reactive protein, and procalcitonin), ICU delirium, ICU sleep quality, and clinical outcomes (encompassing ICU mortality, in-hospital mortality, 28-day all-cause mortality, 90-day all-cause mortality, 90-day readmission rate, and 90-day incidence of secondary infections).

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.