1.Basic principles Nutritional support should be considered when transferred to ICU for ≥ 24 hours and hemodynamically stable; unless disease limitation or treatment needs, in principle, enteral nutrition should be the mainstay; for those who cannot tolerate enteral nutrition, a combined enteral and parenteral route can be adopted; absolute contraindications of enteral nutrition: mechanical, paralytic intestinal obstruction, intestinal fistula; relative contraindications: short bowel syndrome, inflammatory bowel disease, pancreatitis, cholecystitis; Percutaneous fistula for enteral nutrition needing more than 2 months; PICC for parenteral nutrition needing more than 1 month. 2. Choice of modality Transoral nutrition: without tracheal intubation, awake, obeying instructions, cooperative, swallowing function, normal digestive function. Enteral nutrition: with tracheal intubation, abnormal swallowing function, normal intestinal function. Parenteral nutrition via central vein: abnormal intestinal function, or inability of gastrointestinal indwelling catheter or fistula; Parenteral nutrition via peripheral vein: abnormal intestinal function, or inability of gastrointestinal indwelling catheter or fistula, central vein placement is contraindicated. 3. Monitoring (1) Weight calculation Ideal weight Male=50+0.91*(height cm-152.4) Female=45.5+0.91*(height cm-152.4) (2) Nutritional monitoring Nutritional monitoring items and monitoring frequency Items Initial stable Blood routine Every other day Once a week Blood sugar TID TID