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

Background: Critically ill patients are characterized by a hypermetabolic s tate, a catabolic response, higher nutritional needs, and a decreased capac ity 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 bal ance (NB) in mechanically ventilated, critically ill children receiving par enteral nutrition. Design: This was a cross-sectional study in which resting energy expenditur e (REE) and NB were measured and substrate utilization and the metabolic in dex (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), respectivel y. Patients with an MI > 1.1 (n = 19) had a higher fat oxidation than did p atients with an MI < 1. 1 (n = 14; P < 0.05). Patients with lipogenesis (n = 13) had a hip-her carbohydrate intake than did patients without lipogenes is (n = 20; P < 0.05). Patients with a positive NB (n = 12) had a higher pr otein intake than did patients with a negative NB (n = 21; P < 0.001) and l ower 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 carbohydr ate is utilized poorly. A high carbohydrate intake was associated with lipo genesis and less fat oxidation, a negative NB was associated with high oxid ation rates for protein, and a high protein intake was associated with a po sitive NB.