13.1 Energy Needs Across Age & Clinical State

Estimating Pediatric Energy Needs

The anchor reference for healthy children is the Estimated Energy Requirement (EER) from the Institute of Medicine Dietary Reference Intakes (DRIs). The EER is the intake predicted to maintain energy balance in a healthy child of a defined age, sex, weight, height, and physical activity level (PAL), and it deliberately includes an allowance for tissue deposition (growth). For infants 0–36 months the equations are simple and weight-based; for children 3–18 years they incorporate height, age, and an activity coefficient.

DRI EER Equations (IOM)

Physical activity coefficients: for boys — sedentary 1.00, low active 1.13, active 1.26, very active 1.42; for girls — sedentary 1.00, low active 1.16, active 1.31, very active 1.56.

Worked example. A 7-year-old girl, 22 kg, 1.15 m, low active (PA 1.16): EER = 135.3 − (30.8 × 7) + 1.16 × [(10 × 22) + (934 × 1.15)] + 20 = 135.3 − 215.6 + 1.16 × (220 + 1,074.1) + 20 ≈ 1,441 kcal/d.

Energy per Kilogram Declines with Age

A recurring exam concept: resting metabolism and growth velocity per kilogram are highest in early life, so energy needs per unit body weight fall monotonically. A term newborn needs roughly 100–120 kcal/kg/d; by 1 year ~90–100 kcal/kg/d; by school age ~70–80 kcal/kg/d; adolescents converge toward 35–45 kcal/kg/d depending on sex, growth spurt, and activity. Any prescription that gives a teenager the same kcal/kg as an infant signals a dosing error.

Preterm Infant Energy Needs

A stable, growing preterm infant requires approximately 110–130 kcal/kg/d enterally to approximate third-trimester intrauterine accretion (~15–20 g/kg/d weight gain). Extremely low birth weight (ELBW, <1,000 g) infants — with higher resting energy expenditure, greater insensible losses, and immature absorption — may need 130–150 kcal/kg/d. Parenteral energy needs are lower (~90–100 kcal/kg/d) because there is no cost of digestion/absorption and no stool losses. Human milk (~20 kcal/oz unfortified) and standard preterm discharge formulas (22 kcal/oz) typically must be fortified to 24–30 kcal/oz to deliver this within tolerated volumes of ~150–180 mL/kg/d.

Illness, Obesity, and Growth Failure Adjustments

Stress and Activity Factors

Hospitalized and injured children are often prescribed energy as a measured or estimated resting energy expenditure (REE) multiplied by a stress factor. Classic multipliers: uncomplicated surgery ~1.2–1.5, sepsis ~1.2–1.5, traumatic brain injury ~1.3–1.5, and major burns 1.5–2.0 or more. Fever raises REE roughly 10–13% per degree Celsius above 37 °C. A key nuance for the critically ill: sedation, paralysis, and mechanical ventilation reduce activity expenditure, so modern practice favors starting near measured REE and titrating rather than blindly stacking large stress factors — overfeeding carries real harm (hyperglycemia, hypercapnia from excess CO2 production, hepatic steatosis).

Adjusted Body Weight in Obesity

Using actual weight overestimates needs in obesity because adipose tissue is less metabolically active than lean mass; using ideal weight underestimates them. The common compromise is adjusted body weight (AdjBW) = IBW + (0.25 to 0.5) × (actual weight − IBW). Example: a 15-year-old at 90 kg with an IBW of 60 kg gives AdjBW = 60 + 0.25 × 30 = 67.5 kg (factor 0.25) or 75 kg (factor 0.5). Know that the correction factor varies by institution and guideline; the exam tests the construct, not a single mandated coefficient.

Indirect Calorimetry vs Predictive Equations

Indirect calorimetry measures oxygen consumption (VO2) and carbon dioxide production (VCO2) to compute energy expenditure (via the Weir equation) and the respiratory quotient (RQ; fat oxidation ~0.7, mixed ~0.85, carbohydrate 1.0, lipogenesis >1.0). It is the gold standard in mechanically ventilated, critically ill children because predictive equations — EER, Schofield, WHO, White — routinely deviate 20–30% or more from measured values in this population. Indications include failure to wean from ventilation, unexpected growth failure on calculated feeds, severe trauma or burns, and suspected over- or underfeeding. Limitations: air leaks around uncuffed endotracheal tubes, FiO2 >0.60, chest tube leaks, and dialysis invalidate measurements.

Failure to Thrive: Energy Density Strategies

For infants and toddlers with failure to thrive (FTT) who cannot consume adequate volume, raise energy density rather than volume: concentrate formula stepwise from 20 → 22 → 24 → 27 → 30 kcal/oz (standard formula and mature human milk are ~20 kcal/oz ≈ 0.67 kcal/mL), fortify expressed human milk, and add modulars — vegetable oil (~8–9 kcal/g), medium-chain triglyceride (MCT) oil (~7.7 kcal/mL, useful with cholestasis or fat malabsorption), glucose polymers, or protein modulars when the protein-to-energy ratio must be preserved. Recalculate protein and micronutrient adequacy whenever density is raised, increase osmolality gradually, and verify actual intake with calorie counts before escalating.