The choice of enteral nutrition, parenteral nutrition, or combination of both depends to a large extent on the patient's gastrointestinal tract function and tolerance to the manner of which nutrition is supplied, usually according to the nature of the disease and patient's statement and the judgment of the doctor. If the patient's cardiopulmonary function is unstable and most of the gastrointestinal tract absorption function is lost or the imbalance of nutrition metabolism is in urgent need of compensation, parenteral nutrition should be chosen. If the gastrointestinal tract is functional or partially functional, it should be safe to have close to enteral nutrition. Enteral nutrition is a physiological feeding pathway, which avoids the risk of central venous intubation. It can also help restore intestinal function. Its advantages are simple, safe, economical and efficient, in accordance with physiological function. There are a variety of enteral nutrition agents.

However, for patients with gastrointestinal tract disease, it is not very easy to choose the right time to give enteral nutrition safely. Some clinical symptoms, such as nausea, fullness, abdominal pain and signs such as diarrhea, reduced bowel pain, abdominal distention, and so on, restrict the use of enteral nutrition. If the patient cannot tolerate the nasogastric tube placement, the nasogastric tube placement is not smooth or the esophagus, or after gastric surgery the original anatomical position change which one is impossible to place the tube, it will limit the enteral nutrition application. At the same time, enteral nutrition can also have complications, including trachea aspiration, nausea, diarrhea, and intestinal blood supply disorders. Therefore, enteral nutrition should not be given when the heart function is in a marginal state or hemodynamics is unstable. Patients with poor enteral nutrition should change the supply mode in time so as not to delay the treatment of nutrition. In short, the most critical and important principle of enteral nutrition is to strictly control the indications, accurately calculate the amount and duration of nutritional therapy, and choose the proper way of nutritional therapy. Parenteral nutrition is an active and effective adjuvant therapy for almost digestive system disease that is inadequate, inappropriate or impossible to feed through the mouth. It is an important step forward in the treatment of diseases, which have benefited patients with digestive diseases such as malnutrition and gastrointestinal dysfunction.

Because parenteral nutrition can produce full feeling syndrome and make gastric peristalsis inhibition, it is advocated that it is necessary to make it slightly hungry for a few days before transition to the intestine. Intravenous infusion of liquid which can keep water and electrolyte balance stimulates gastrointestinal activity. At the same time conditioned reflex with the help of dishes color, fragrance, taste stimulate appetite. Or patients have a pleasant meal with the family. This principle should also be followed for transition from parenteral feeding to enteral nutrition.

Long-term parenteral nutrition can lead to a decline in gastrointestinal function. Therefore, the transition from parenteral nutrition to enteral nutrition must be gradually carried out. This transition can be divided into four stages: ①parenteral nutrition with tube-feeding together; ②tube feeding alone; ③combination of tube feeding and oral feeding; ④normal enteral nutrition. It should be gradually transferred to enteral nutrition to make intestinal cells adapt. When enteral feeding can be tolerated, low concentration should be used first. Slow infusion of essential enteral nutrition or non-essential enteral nutrition is to monitor water, electrolyte balance and nutrient intake (including parenteral and enteral intake). The parenteral nutrition was not completely removed until the enteral nutrition could meet the need of metabolism. Tube feeding was combined with oral feeding and finally the normal enteral nutrition was obtained.