Energy Needs of Very Low Birth Weight Infants

 Background
 Meeting Energy Needs of Individual Infants

Background

Many VLBW infants establish appropriate weight gain patterns in the hospital with energy intakes of 120-130 kcal per kg of body weight per day. Infants with cardiac and respiratory problems may have higher energy needs of up to 150 kcal/kg/d.

In full-term, healthy infants energy intakes per unit of body weight fall from about 118 kcal/kg/d at one month of age to about 92 kcal/kg/d at 6 months of age (Fomon, 1993). The DRIs provide equations for estimating energy requirements (EER) for infants and children of normal weight. These equations are based on studies using doubly labeled water and include energy needed for growth. Energy coefficients are included in the equation for children >3 years of age.

Table: Estimated Energy Requirement (EER) Equation for estimating DRI for Energy

Table: Sample EER Calculations at given weight ranges *

Energy needs for VLBW infants may or may not be similar to full-term healthy infants. After the neonatal period, energy needs are influenced by several factors. These include:

• Activity: Some VLBW infants with neurological problems may require less energy intake if movement is limited.
• Resting Energy Expenditure: Resting energy requirements are lower in mechanically ventilated infants who do not need to support the energy cost of breathing.
• Diseases of prematurity: Energy requirements may be increased with ongoing respiratory or cardiac problems.
• Growth: Infants who exhibit catch-up growth may continue to gain weight at rates of 20-30 g per day (see incremental growth). These infants will benefit from higher energy intakes to support and promote growth. Other infants may have lower incremental growth than expected due to limitations imposed by diseases of prematurity or other factors.
• Proportionality of growth. If energy intake is high, some infants may gain weight, but not grow proportionately in length. While some degree of disproportionate weight gain for length may be beneficial in the first months of life, excessive increases in weight for length over a long period indicate a need to reevaluate energy needs.

Meeting Energy Needs of Individual Infants

One approach to ensuring that energy needs are met is to start with an assumption that the infant will need 120-130 kcal/kg/d. Intake recommendations can then be adjusted as indicated by the individual infant's intake and subsequent growth.

In order to achieve an intake of >120 kcal/kg/d the infant must be able to consume a total of more than 180 cc of formula or breastmilk per kg of body weight per day (2.7 oz formula or breastmilk per pound body weight per day). If this level of intake is not possible due to limitations associated with feeding, alternative methods of meeting energy needs should be considered. See section on Enteral Feeding and Concentrating Formula.

The following table provides indications of the total intake that would be required to provide 120 kcal/kg/d with formulas mixed at both 20 and 24 kcal/oz. Twenty kcal per ounce is assigned as a mean value for human milk as well as the energy density of standard infant formula. To achieve a density of 24 kcal/oz, formula is concentrated or supplements are added to breastmilk (see Concentrating Infant Formula).

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