Energy metabolism, nitrogen balance, and substrate utilization in critically ill children

Am J Clin Nutr. 2001 Nov;74(5):664-9. doi: 10.1093/ajcn/74.5.664.


Background: Critically ill patients are characterized by a hypermetabolic state, a catabolic response, higher nutritional needs, and a decreased capacity for utilization of parenteral substrate.

Objective: We sought to analyze the relation between a patient's metabolic state and their nutritional intake, substrate utilization, and nitrogen balance (NB) in mechanically ventilated, critically ill children receiving parenteral nutrition.

Design: This was a cross-sectional study in which resting energy expenditure (REE) and NB were measured and substrate utilization and the metabolic index (MI) ratio (REE/expected energy requirements) were calculated.

Results: Thirty-three children (mean age: 5 y) participated. Their average REE was 0.23 +/- 0.10 MJ x kg(-1) x d(-1) and their average MI was 1.2 +/- 0.5. Mean energy intake, protein intake, and NB were 0.25 +/- 0.14 MJ x kg(-1) x d(-1), 2.1 +/- 1 g x kg(-1) x d(-1), and -89 +/- 166 mg x kg(-1) x d(-1), respectively. Patients with an MI >1.1 (n = 19) had a higher fat oxidation than did patients with an MI <1.1 (n = 14; P < 0.05). Patients with lipogenesis (n = 13) had a higher carbohydrate intake than did patients without lipogenesis (n = 20; P < 0.05). Patients with a positive NB (n = 12) had a higher protein intake than did patients with a negative NB (n = 21; P < 0.001) and lower protein oxidation (P < 0.01).

Conclusions: Critically ill children are hypermetabolic and in negative NB. In this population, fat is used preferentially for oxidation and carbohydrate is utilized poorly. A high carbohydrate intake was associated with lipogenesis and less fat oxidation, a negative NB was associated with high oxidation rates for protein, and a high protein intake was associated with a positive NB.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adolescent
  • Basal Metabolism
  • Calorimetry, Indirect
  • Child
  • Child, Preschool
  • Critical Illness*
  • Cross-Sectional Studies
  • Dietary Carbohydrates / administration & dosage
  • Dietary Carbohydrates / metabolism*
  • Dietary Fats / administration & dosage
  • Dietary Fats / metabolism*
  • Dietary Proteins / administration & dosage
  • Dietary Proteins / metabolism*
  • Energy Metabolism*
  • Female
  • Humans
  • Infant
  • Male
  • Nitrogen / metabolism*
  • Nutritional Requirements
  • Parenteral Nutrition
  • Respiration, Artificial
  • Substrate Specificity


  • Dietary Carbohydrates
  • Dietary Fats
  • Dietary Proteins
  • Nitrogen