This study aims to address the challenges of enteral nutrition support in critically ill ICU patients with varying gastrointestinal function. We'll use bedside Doppler ultrasound to monitor superior mesenteric artery (SMA) blood flow changes post - feeding, exploring its correlation with Acute Gastrointestinal Injury (AGI) and other hemodynamic indicators. Our goals are to identify the patterns of SMA blood flow changes, establish a predictive model linking SMA blood flow reactivity to AGI risk, and propose individualized enteral nutrition strategies based on intestinal hemodynamics. Through this innovative approach, we hope to enhance the safety of enteral nutrition, reduce AGI incidence, and improve patient outcomes.

Inclusion Criteria:

• Adults aged ≥18 years and ≤80 years.
• Admitted to the study with a expected stay of more than 72 hours.
• Require initiation of enteral nutrition support.

Exclusion Criteria:

• Pre-existing severe gastrointestinal diseases.
• Patients with gastrointestinal bleeding.
• Patients with bowel obstruction.
• Pregnant or lactating women.
• Patients with contraindications to bedside Doppler ultrasound.

The study population will be selected from adult patients admitted to the ICU. Participants will be those aged between 18 and 80 years old, with an expected ICU stay of more than 72 hours after enrolled, and who require the initiation of enteral nutrition support. These patients are at risk of gastrointestinal dysfunction and acute gastrointestinal injury (AGI), making them suitable candidates for a study focused on optimizing enteral nutrition strategies and monitoring gastrointestinal blood flow.