It is generally accepted that clinical nutrition support includes the provision of a full range of nutrients to patients by oral, intestinal or parenteral routes. Currently, clinical nutrition includes enteral nutrition and parenteral nutrition. EN refers to complete nutrients administered by tube through the gastrointestinal tract; PN is the intravenous infusion of amino acids, fats and sugars, also known as total parenteral nutrition. In the literature of randomized controlled studies evaluating the clinical effectiveness of PN, the two methods of glucose electrolyte infusion (5% GNS) versus total parenteral nutrition are commonly used. PN support should be given when patients are unable or unwilling to eat normally for various reasons, and when patients with malnutrition or at nutritional risk have inadequate oral delivery of nutrients. Nutritional support is never an emergency management measure and should be administered only after the patient’s vital signs have stabilized according to the specifications of indications and use. A PN main preparations 1, carbohydrate preparations This is the most simple and effective PN preparations, which can provide 50%-60% of the body’s metabolic energy requirements. Glucose is the most commonly used energy preparation for PN, often formulated clinically into 5%, 10%, 50% and other specifications of the injection. Clinically used preparations are also fructose, maltose and sugar alcohols (such as sorbitol and xylitol). But these preparations can not be applied in large quantities for a long time, otherwise it will cause hyperlactatemia, hyperbilirubinemia, hyperuricemia and other metabolic disorders. At present, it is no longer advocated to apply glucose preparations alone, but to combine with fat emulsions to reduce the amount of glucose and avoid the occurrence of glucose metabolism disorders. In addition, when a large amount of glucose is infused, the appropriate amount of insulin needs to be supplemented to make up for the shortage of endogenous insulin, and the daily glucose dosage should not exceed 400g. 2, fat emulsion Fat emulsion is an important energy substance, and the energy supplied can account for 25%-50% of the total energy. At present, there are a variety of fat emulsions, including soybean oil or safflower oil by phospholipid emulsification and the addition of injectable glycerin made of fat emulsion is most commonly used, the solution of fat particles in the particle size and biological characteristics and natural celiac particles are similar, stable physicochemical properties. In addition, the number of carbon atoms of triglycerides varies with the composition of fat emulsions, which can be divided into long-chain triglycerides, medium-chain triglycerides and short-chain triglycerides according to the length of carbon chains. Long-chain triglycerides can provide essential fatty acids and energy for the human body, with a slow oxidative metabolism rate, and are mainly used for the nutrition of patients with renal failure, acute necrotizing pancreatitis, trauma and other serious illnesses, and the treatment of premature infants. However, medium-chain triglycerides are especially suitable for critically ill patients and those with poor liver function, and are safer for neonatal treatment, but they cannot provide essential fatty acids, and large infusion may cause metabolic acidosis and neurological side effects. Clinically, it is safer for some special patients (such as severe trauma, infection, liver insufficiency, etc.) to use a physical mixture of long-chain triglycerides and medium-chain triglycerides in half of the amount to avoid the shortcomings. 3.Amino acid preparation Amino acid is the basic substance for synthesizing protein, which can enter the tissue cells under the condition of sufficient energy supply, participate in the anabolism of protein, and generate enzymes, hormones, antibodies, structural proteins and other substances, thus promoting tissue healing and restoring normal physiological functions. Different amino acid preparations have different clinical effects due to different compositions. Nutritional compounded amino acids are most frequently used, mainly for nutritional support in patients with hyperactive muscle catabolism, digestive system disorders, nutritional deterioration and decreased immune function before and after surgery, trauma, extensive burns, severe infections and other stressful conditions. In addition, the role of individual amino acids such as glutamine in PN has received much attention. When DE support is applied to many conditions, patients may experience a depletion of glutamine in their bodies. Glutamine is the most abundant non-essential amino acid in the body. Exogenous supplementation of glutamine increases its blood concentration, provides important oxidative fuel for rapidly proliferating cells (such as intestinal epithelial cells, lymphocytes and neutrophils) and non-proliferating cells (such as macrophages), promotes glutamine uptake and utilization by intestinal mucosal epithelial cells and their associated lymphocytes, and promotes T-cell synthesis. 4.Vitamins are one of the indispensable components of PN, which are water-soluble and fat-soluble and mainly maintain normal metabolism and physiological functions of human body. Most of the vitamins used in PN are compound preparations. 5. trace elements Trace elements are mainly involved in oxygen storage and electron transfer, and in genetic and free radical regulation. Because the body needs very little trace elements, short-term fasting people do not need to supplement, if the fasting for more than a month should be supplemented, pregnant women also have a mildly increased need for trace elements. 6, electrolytes Electrolytes are an important substance for maintaining water, electrolyte and acid-base balance in the body, keeping the internal environment stable, maintaining various enzyme activities and nerve and muscle stress as well as normal nutrient metabolism. Clinically used preparations include 10% sodium chloride solution, 10% sodium chloride solution, 10% potassium chloride solution, 10% calcium gluconate solution, calcium chloride solution, 25% magnesium sulfate solution, sodium bicarbonate solution, etc. If necessary, monosodium glutamate, potassium glutamate, phosphorus preparations can be added. Phosphorus is closely related to energy metabolism and protein synthesis, not only involved in the formation of bone, and participate in the composition of cell membranes, the body may occur when the lack of hypophosphatemia. 7.Total nutrition mixture Total nutrition mixture (TMA) is made by mixing carbohydrates, fat emulsion, amino acids, vitamins, trace elements, electrolytes and water and other nutrients required for PN in a certain ratio according to the patient’s needs in a glass bottle or plastic bag; The physical and chemical environment of TMA is not conducive to bacterial growth and can reduce the complications of high concentration glucose infusion; in addition, TMA can improve the oxidation of long-chain fatty acids in fat emulsions and avoid the adverse effects of too rapid fat emulsion infusion. In conclusion, TMA brings great convenience and safety to clinical PN support.