Predictive Value of Gastrointestinal Blood Flow for Enteral Nutrition Intolerance in Critically Ill Patients

Inclusion Criteria: * Age \> 18 years old. * Expected duration of enteral nutrition support \> 7 days. * Patients or their legal representatives sign the informed consent form. Exclusion Criteria: * History of major gastrointestinal surgery such as subtotal gastrectomy and gastrointestinal anastomosis. * Contraindications to abdominal point-of-care ultrasound (POCUS) examination (e.g., recent large-area abdominal burns, dressings blocking movement, open abdomen). * Presence of severe gastrointestinal diseases such as gastroparesis, intestinal obstruction, digestive tract perforation, and gastrointestinal bleeding upon admission. * Presence of severe peripheral vascular disease or valvular heart disease. * Pregnant or lactating women.