1.Characteristics of colorectal cancer with obstruction and the necessity of its perioperative nutritional support Colorectal cancer is a common gastrointestinal tumor, and the symptoms of obstruction may appear successively according to different lesion sites. The patients in this group are all in stage B and C, and 11 cases in stage C account for 65% (11/17). Since cancerous colorectal obstruction is “closed-collar obstruction”, some patients need to undergo emergency surgery, while others need to undergo surgery within a short period of time. The chronic consumption of malignant tumor for a long time, the influence of other underlying diseases, the disturbance of the internal environment such as water, electrolytes and body metabolism due to intestinal obstruction, and the obvious increase of the body’s need for calories and proteins during surgical stress, together with the inability of patients to eat normally, may lead to different degrees of malnutrition. The indexes of Hb, TLC, Alb, PA, TRF serum potassium measured before PN in Table 2 were significantly lower than normal values, suggesting that obstructive colorectal cancer is more prone to metabolic disorders and malnutrition. Due to the special characteristics of tumor diseases, long-term standardized nutritional support cannot be provided before surgery, and short-time nutritional support cannot completely correct the malnutrition associated with patients with obstructive tumors. Malnutrition and hypoproteinemia have been shown to be significantly associated with postoperative morbidity and mortality and complication rates in oncology patients, and nutritional support can improve the tolerance of GI tumor patients to surgical trauma and facilitate bowel preparation. Therefore, reasonable perioperative nutritional support is necessary for patients with obstructive colorectal cancer. 2.Rational application of nutritional support for patients with obstructive colorectal cancer Usually, when malnutrition is caused by benign diseases, enteral nutrition is the preferred route of support, because the purpose of nutritional support is not only to improve nutritional status, but also to restore and maintain gastrointestinal function. Most of the patients with obstructive colorectal cancer have gastrointestinal dysfunction, and the gastrointestinal dysfunction caused by tumor obstruction often needs to be solved by emergency or limited surgery. On the other hand, fasting and gastrointestinal decompression can cause or aggravate the loss of digestive fluid, resulting in different degrees of water and electrolyte imbalance. Therefore, unlike other benign diseases, PN may be the main form of perioperative nutritional support for patients with obstructive colorectal cancer. Since preoperative nutritional support is time-critical, after 24-48h of symptomatic treatment and basic correction of water-electrolyte-acid-base balance disorder after admission, parenteral nutrition can be started even if the obstruction is not relieved, and it is not necessary to wait for the obstruction to It is not necessary to wait until the obstruction is completely relieved before enteral nutrition is performed. Except for some patients with advanced hyperemesis and other underlying diseases, patients with colorectal cancer with obstruction usually have good function of other important organs, and their glucose tolerance and fat contouring ability are basically normal, so they can generally tolerate nutrition support better. In addition, the transition to full volume can be made as soon as possible to facilitate the preoperative nutritional improvement of these patients. Due to the reasonable support program, no liver and kidney function damage caused by nutritional support was found in this group, and the indexes of blood glucose, blood lipid and serum muscle ration did not change significantly compared with those before support (P>0.05). Therefore, for patients with obstructive colorectal cancer, perioperative nutritional support based on parenteral nutritional support and supplying adequate calories and nitrogen is effective and safe.