With the rapid development of neonatal medicine, the survival rate of preterm and low birth weight infants has been increasing, among which the improvement of nutritional conditions has played an important role. since the 1980s, intravenous nutrition has been widely used in neonatal care centers in developed countries to meet the nutritional needs of preterm infants. After 10-20 years of clinical practice and laboratory studies, it is now believed that the dependence on a single intravenous nutrition should be changed and non-nutritive sucking and early microfeeding should be enhanced to improve the nutrition and prognosis of preterm infants in the early nutrition approach. I. Nutritional goals of preterm infants Nutritional goals are the most basic issues in preterm infant nutrition. There is no unified standard that is generally accepted. At present, the ideal nutritional goals include: (1) to achieve recent growth and development standards (with reference to the composition of the fetal body. (2) prevention of feeding-related diseases (feeding intolerance, NEC, viral infections, etc.); (3) achievement of the best long-term results (promotion of neuropsychiatric development, reduction of allergies and atopic diseases, etc.). Reduce the incidence of allergies and atopic diseases and diseases affecting adults such as hypertension, heart disease, hypercholesterolemia, etc.). (2) Clinical management of preterm infant feeding (1) Milk selection: 1. Preterm infant breast milk: Fresh preterm infant breast milk is different from full-term infant breast milk within 1 month after birth: (1) Breast milk protein of 30-34 weeks preterm infant within 10 days after birth: total protein is 47.9mg/ml on the first day after birth, 21.9mg/ml on the 10th day, only whey protein within two days after birth, and only monitored on the 3rd day The ratio of whey to casein was 86:14 on the first day of life, and 70:30 on the 10th day of life (total protein in colostrum of full-term infants was 27 mg/ml, including 15 mg/ml of lactoglobulin and 12 mg/ml of casein). (2) Na content in breast milk per 100 ml was 2.66±0.3 mmol/L. 0.3mmol/L, which decreased to 0.76±0.09mmol/L by the end of 1 month. (3) The fat and lactose content was low, and the calorie content was slightly lower. It is (215±10) kJ per 100 ml of breast milk. (4) The calcium content is low, especially not meeting the growth needs of preterm infants <1500g. Therefore, the amount of protein, sodium and calcium in breast milk of preterm infants has been significantly insufficient after 1 month. Boston Children's Hospital routinely recommends breastfeeding of preterm infants with gestational age less than 32 Weeks/birth weight less than 1500g. 2, preterm formula: The common features of various preterm formula are, for example, per 100ml of formula: (1) protein 1.92-2.2g, whey protein to casein ratio of 60:40 or 70:30, supplying sufficient amount of cystamine. (2) 3.41-4.0g of fat, of which 40% are medium-chain fatty acids, which are easily digested and absorbed. 418.4kJ of linoleic acid is higher than the required amount (300mg), which is beneficial to promote the growth and development of infant brain cells. (3) 60% of carbohydrates are polydextrose, supplying the required heat without increasing blood osmolarity, making milk isotonic 290mOsm/(kg, H2O). (4) Increase the sodium content to supplement the increased renal sodium excretion of preterm infants. (5) Calcium content is 3 times the normal breast milk content, making Ca:P close to 2:1. (6) Vitamin E > 1 IU, protecting cell membranes and preventing lipid peroxidation. Boston Children’s Hospital routinely recommends preterm formula feeding for newborns with gestational age greater than 32 Weeks/birth weight greater than 1500 g. The formula can be used to feed preterm infants, but it lacks many of the growth factors, enzymes, IgA and macrophages found in breast milk. (B) Feeding methods: 1. Early feeding is generally advocated to shorten the time and reduce the degree of physiological weight loss, reduce the incidence of hypoglycemia, and relatively reduce the concentration of blood bilirubin. Birth weight > 1500g, no obvious lung disease infants can start feeding within 12-24 hours after birth. Perinatal asphyxia, maternal gestational hypertensive syndrome or very low birth weight children should delay feeding for at least 72 hours. 2, feeding methods (1) intermittent gastric tube method. (2) Continuous gastric tube method. (3) over the pylorus feeding (through the nasoduodenum or nasojejunal). 3, each dose varies according to body weight: weight ≤ 1000g, 1-2ml/kg; 1001-1500g, 2-3ml/kg; 1501-2000g, 3-4ml/kg; >2000g, 10ml/kg. 4, feeding interval: can be arranged according to body weight, generally weight below 1000g, feed every hour; 1001-1500g, every 1.5 hours. 1500g, once every 1.5 hours; 1501-2000g, once every 2 hours; 2001-2500g, once every 3 hours. 5.Increase the amount of milk ≤ 20ml/kg per day, and the tolerance must be evaluated when increasing the milk. 6.After feeding, it is best to lie on the right side and pat the back to promote gastric emptying. 7.Record fluid intake and output in detail, measure body weight at least once a day, and record feeding type and tolerance. (iii) Feeding tolerance: Each preterm infant has different nutritional needs, and the feeding program should vary from person to person. When increasing the amount of milk. If one of the following conditions occurs, feeding intolerance can be considered: 1. Observe the amount of gastric residue: for infants fed by gastric tube, the amount of residual milk in the stomach should be taken before each feeding, and the normal amount is 0-2 ml/kg. The amount of residue should be reduced or stopped once when the amount exceeds 1/3 of the last feeding or when the amount exceeds 1 h during continuous feeding. 2.Observation of abdominal distension: intermittent measurement of abdominal circumference, fixed measurement site and time. Abdominal circumference increased by 1.5cm with intestinal type should be reduced or stop feeding once. 3, vomiting, abdominal distension, increased gastric residue, gastric residue contaminated with bile, bloody stool or fecal occult blood, suggesting infection or necrotizing small intestinal colitis, should stop feeding through the mouth. 4, the occurrence of apnea and bradycardia increased significantly and stool thinning. Reduced material more than 2% (lactose malabsorption) also suggests feeding intolerance. Gastric residuals above normal and bloating are important indicators of feeding intolerance. To enhance intestinal motility, glycerol liquid enemas several times a day are feasible; if they are ineffective, enema angiography may be chosen as diagnostic treatment when NEC and infection are excluded. If enucleogram is still not effective, erythromycin continuous drip can be chosen. The dosage of erythromycin is 10-20mg/kg/d and changed to 3mg/kg/d after several days, which is 1/10 of the usual amount. The significance of early microfeeding for preterm infants 1. Early microfeeding makes the neonatal intestinal cavity receive nutrition directly, which is necessary for the integrity of gastrointestinal structure and function. 2, early microfeeding will not increase the incidence of aspiration pneumonia, necrotizing small intestinal colitis. 3.Early microfeeding helps to improve feeding tolerance of newborns, promote intestinal motility and bilirubin excretion in feces, reduce the chance of jaundice phototherapy, and reduce physiological weight loss. Non-nutritive sucking and neonatal growth and development 1. Non-nutritive sucking can promote the growth and development of the gastrointestinal tract and the maturation of gastrointestinal function. 2.Non-nutritive sucking can improve the secretion of gastrointestinal hormones in newborns.