Metabolic complications: (1) Abnormal water metabolism: The most common type of enteral nutrition support is hypertonic dehydration, with a clinical incidence of about 5-10%. This complication occurs mostly in tracheotomized patients, comatose and frail elderly patients, and young children, because these patients often have combined renal insufficiency. These patients are more prone to dehydration if they are on hypertonic and high-protein formulas for gastrointestinal nutrition support. Once this complication occurs, it is important to monitor electrolytes and adjust them accordingly, in addition to adding water to the gastrointestinal nutrition solution as appropriate. In some patients with cardiac, renal and hepatic dysfunction, especially in elderly patients, water and sodium intake should be strictly limited during the implementation of enteral nutrition support, otherwise water retention will occur. (2) Abnormal glucose metabolism: Hyperglycemia or hypoglycemia may occur during enteral nutrition support. Those who receive high calorie feeding, or decreased glucose tolerance under stress can lead to hyperglycemia or diabetes. Non-ketotic hypertonic hyperglycemia is most often seen in patients during acute episodes of diabetes or in those with past occult diabetes, mainly due to a relative lack of insulin. Non-ketotic hyperosmolar hyperglycemia is mostly preventable with close monitoring. Once this complication occurs, the original nutritional solution should be discontinued immediately and exogenous insulin should be used to control blood glucose, and then re-institute intragastric nutritional support after blood glucose stabilization. Hypoglycemia mostly occurs in patients who apply elemental diet for a long time and stop suddenly. Slowly stopping enteral nutrition or supplementing with appropriate amount of sugar in other forms after stopping can avoid the occurrence of hypoglycemia. (3) Electrolyte and trace element abnormalities: The most common abnormality is blood potassium, which is mainly caused by high potassium content in some nutrition solutions or poor renal function of patients. Hypokalemia is commonly caused by catabolic state, depletion of lean tissue groups in the body, metabolic alkalosis, or failure to supplement potassium in a timely manner due to the need for insulin. When high doses of diuretics are applied and ADH levels are increased, attention should be paid to prevent the occurrence of hyponatremia. Deficiencies of serum trace elements zinc and copper, but generally rarely appear clinically as typical symptoms. Once the deficiency of trace elements appears, it can be easily corrected with proper supplementation. At present, enteral nutrition commercial preparations all contain a certain amount of trace elements, which can meet the daily needs of patients for trace elements. (4), acid-base balance disorder: acid-base balance disorder is less common in enteral nutrition, mainly related to the application of inappropriate preparations or to the primary disease. In patients with chronic obstructive pulmonary disease or patients who have just stopped mechanical assisted ventilation and have difficulty in carbon dioxide expulsion, hypercarbia can occur with excessive caloric or high carbohydrate intake. Therefore, in patients mentioned above, overfeeding should be avoided, and special preparations for pulmonary diseases should be selected to increase the proportion of calories from fat and decrease the proportion of calories from carbohydrates. (5), abnormal liver function: when gastrointestinal nutrition support is performed, it is often accompanied by elevated transaminases. However, once the gastrointestinal nutritional support is discontinued, liver function can be restored. This transaminase elevation is non-specific, which may be caused by the breakdown of amino acids in the nutrient solution into the liver, resulting in toxicity to hepatocytes, or may be caused by the absorption of a large amount of nutrient solution into the liver, stimulating the new activity of the enzyme system in the liver. (6), re-feeding syndrome: re-feeding syndrome for the depletion state to provide nutritional support after the emergence of metabolic, physiological change phenomenon, manifested as low phosphorus, low magnesium, low potassium and sugar metabolism abnormalities and imbalance, and further lead to the body organs and systems abnormalities. The best treatment for refeeding syndrome is prevention. Before nutritional support, electrolyte balance should be corrected, circulatory volume should be gradually restored, and the manifestations of heart failure should be closely monitored; and then nutritional support should be started, starting from low doses and progressing gradually, while water, electrolytes and metabolic responses should be closely monitored.