Very low birth weight (VLBW) infants are at high risk of growth failure as compared with their full-term, age-matched peers. The provision of adequate caloric intake, with proportional carbohydrates, proteins, and lipids, is crucial to optimizing growth of these fragile infants while also optimizing fluid balance. During the first days of life, these infants receive the majority of their nutrition via parenteral nutrition (PN) while enteral feedings are advanced. Careful management of the components of PN is essential to promote adequate postnatal growth and to minimize PN-related complications.
To provide guidance for neonatologists and trainees rotating through the neonatal intensive care unit (NICU), advanced practitioners, neonatal dietitians, and neonatal nurses regarding management of PN for VLBW infants.
As noted above, VLBW infants are at an increased risk for growth failure. Observational studies have noted that VLBW infants with a diagnosis of extrauterine growth failure, defined as weight less than the 10th percentile at a corrected gestational age of 36 weeks, have impaired neurodevelopmental outcomes compared with those infants without a diagnosis of growth failure. Many factors contribute to growth failure in the NICU, and these factors can be divided broadly into inadequate caloric input and excessive caloric output. Ideally, PN would mimic nutrition provided to the fetus in utero. However, during the first few days of life, the administration of optimal PN is often limited by critical illness and metabolic immaturity, combined with fluid intake restriction and limited central IV access for preterm infants, especially those <1 kg at birth. Once enteral feeding is initiated, PN is weaned as the feeding volume is advanced. This transitional period is one of the most nutritionally vulnerable time points for VLBW infants. A retrospective, observational study demonstrated that during this time, protein intake from a combination of total parenteral nutrition (TPN) and enteral feeding is often inadequate. Poor growth velocity during this transitional period is predictive of later diagnosis of growth failure. Given the constraints of administering PN to preterm infants, meticulous attention must be paid when reviewing and prescribing the content of daily PN formulations. In this chapter, we review evidence-based recommendations for early initiation of PN, provision of macronutrients and micronutrients via PN, monitoring guidelines, and considerations for weaning PN during feed advances.
EARLY PARENTERAL NUTRITION
Delay in initiation of PN contributes to the protein deficit that VLBW infants can accumulate. VLBW neonates receiving only dextrose fluids can lose 1% of body protein stores per day. The provision of calories in excess of basal metabolic rates via PN has been shown to improve weight for age to greater than the 10th percentile at 36 weeks. Providing a minimum of 50 kcal/kg, starting within 2 hours of birth, is considered safe and is equivalent to resting metabolic rates, but additional energy is needed to support growth. Neutral nitrogen balance can be achieved with an initial protein intake of 1–1.5 g/kg/day of protein, but 2.5−3 g/kg/day is recommended to promote a positive nitrogen balance and is considered safe.
The total energy requirement for a VLBW infant is determined by basal energy needs as well as the energy required for growth. VLBW infants need 90–115 kcal/kg/day from PN to support both. Provision of adequate energy intake prevents the use of protein as a fuel source and thereby increases its availability for the synthesis of lean mass.
The fetus receives a constant transfer of glucose from the ...