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

Abstract

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·kg-1 · d-1 and their average MI was 1.2 ± 0.5. Mean energy intake, protein intake, and NB were 0.25 ± 0.14 MJ·kg-1·d-1, 2.1 ± 1 g±kg-1·d-1, and -89 ± 166 mg·kg-1·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.