infant nutrition

Initiating and maintaining the growth infants withe extremely low birth weight (ELBW) is a continuing challenge. Infants are commonly weighed daily, and body length and head circumference are usually measured weekly to track growth. The growth rate often lags because of complications such as pulmonary disease and sepsis.
An additional contributing factor is inadequate caloric and protein intake. Concern that early feeding may be a risk factor for necrotizing enterocolitis (NEC) often defers initiation of enteral feeding, although nutritional management of such infants is marked by a lack of uniformity of practice.

Parenteral nutrition

Parenteral nutrition may provide the primary source of energy and protein in infants with extremely low birth weight in the first few weeks after birth. Optimal parenteral nutrition is achieved by use of a specialized solution consisting of amino acids, dextrose (sugar), minerals, and electrolytes, called total parenteral nutrition (TPN). A 20% lipid emulsion is often run separately to complete the nutrition of the infant. Lipid intake may vary from 1-4g/kg/day (as tolerated) and should be started in the first 24 hours of life for optimal nutrition.
Theoretical concerns regarding infection and hyperbilirubinemia frequently lead to a delay in the initiation of lipid supplementation.
Because these infants lose at least 1.2g/kg/day of endogenous protein, they require at least that amount of amino acid and 30kcal/kg/day to maintain protein homeostasis. Recommendations advocate for initiation of protein supplementation within the first 12-24 hours to avoid protein catabolism.
Some investigators postulate that total daily need to approximate fetal protein accretion rates in these infants may be as high as 4g/kg/day. Evidence to date suggests that early and higher amino acid provision is well tolerated by most infants with extremely low birth weight. Such provision of amino acids will positively affect the plasma amino acid concentrations during the first postnatal week but does not necessarily translate into a significant difference in postnatal growth in the first 28 days.^{[9, 10]}
These infants also need essential amino acids, such as cysteine, and may require glutamine, found in human breast milk but not always present in parenteral nutrition mixtures.
Trace minerals, such as iron, iodine, zinc, copper, selenium, and fluorine, are beneficial as well. Early evidence suggests that chromium, molybdenum, manganese, and cobalt may need to be added to the nutritional regimen, especially in infants who require long-term parenteral nutrition. Some centers also add L-carnitine.
Prolonged use of parenteral nutrition may result in cholestasis and elevated triglyceride levels. To reduce these complications, regular laboratory tests are usually obtained to evaluate liver function, alkaline phosphatase levels, and triglyceride levels.

Enteral nutrition

Enteral feeding is often begun when the infant is medically stable, using small-volume trophic feeding (approximately 10mL/kg/day) to stimulate the gastrointestinal (GI) tract and prevent mucosal atrophy. Bolus feedings every 2-4 hours may begin as early as day 1. If tolerated, as evidenced by minimal gastric residuals and clinical stability, feeding may increase by as much as 10-20mL/kg/day, although feeding practices widely vary. Although bolus feeding may appear to be more physiologically appropriate, infants who do not tolerate the volume of the bolus may be continuously fed.
Clinical studies have consistently demonstrated that infants who are fed earlier and are advanced according to a feeding plan have less incidence of infection and achieve full enteral feeds sooner than counterparts who are less systematically treated. Although the fear of precipitating necrotizing enterocolitis (NEC) remains widespread, randomized, controlled trials have repeatedly failed to show any relationship between feeding practices (ie, age at initiation, rapidity of advancement, caloric density) and the occurrence of NEC.
Breast milk is considered to be the best choice for enteral feeding and has been shown to have protective effects against NEC. Infants with low birth weight have a high need for macronutrients and micronutrients that approaches intrauterine needs; at the same time, their functionally immature GI tract precludes adequate enteral intake.
Despite its many immunologic and nutritional advantages, an exclusive diet of unfortified breast milk may provide insufficient quantities of energy, protein, calcium, and phosphorous to support the goals of intrauterine bone mineralization and growth rates in small, premature infants. Consequently, breast milk must be fortified to provide additional calories, protein, and minerals to promote proper growth. Failure to provide adequate amounts of these essential nutrients, especially calcium and phosphorus, may result in protein malnutrition, hyponatremia, osteopenia of prematurity, or rickets.
Human milk may be supplemented by adding liquid or powder commercially available fortifiers, premature infant formulas, modular supplements, or vitamin/mineral supplements. Commercially available multinutrient fortifiers include Enfamil Human Milk Fortifier (Mead Johnson Nutritionals; Evansville, Indiana) or Similac Human Milk Fortifier (Ross Products, Abbott Laboratories; Columbus, Ohio), both of which are powders. The 2 formulations have some significant differences in their compositions, which may be clinically important. Similac Natural Care Liquid Fortifier (Ross Products) is also available.
Comparisons of the nutrient content and source of macronutrients of these fortifiers have been published. Potential complications of human milk fortifiers include nutrient imbalance, increased osmolarity, and bacterial contamination. Numerous specially formulated preterm formulas are available that have been shown to promote proper growth when breast milk is not available.
Balance of nutrients is very important in early nutrition. Studies suggest that a high carbohydrate neonatal diet is linked to greater weight gain and reduced insulin sensitivity in extremely preterm infants, making them at risk for metabolic syndrome later in life.