Background:Critically ill patients usually are catabolic, as assessed by nitrogen balance (NB) studies. When indirect calorimetry (IC) and total urinary nitrogen (TUN) are done simultaneously; carbohydrate (CHO), protein (PROT), and fat utilization can be calculated. Methods: This study measured NB and substrate utilization in 20 critically ill children(mean PRISM and TISS scores of 8±5 and 30±7 respectively) on mechanical ventilation (MV), in relation to their resting energy expenditure(REE) and caloric intake (Cal In.). All patients were receiving TPN or enteral nutrition when evaluated. REE was measured by IC (mass spectrometry) and TUN by the Kjeldahl method. Expected energy requirements (EER) were obtained from Talbot's tables. REE/EER index > 1.1 defined a hypermetabolic state. Substrate utilization rates were calculated using the Consolazio formulas. Studies were done at the time of the first evaluation and repeated (n=48). The correlation was measured by Pearson's correlation coefficient. Values are mean±SD.

Table 1 No caption available.
Full size table

Conclusions: Moderately critically ill children on mechanical ventilation are hypermetabolic, and in negative nitrogen balance. This population preferentially uses fat for oxidation, carbohydrate is poorly utilized, and the increased urinary nitrogen excretion is correlated with the hypermetabolic state. We speculate that the nutritional intake in this population should contain less carbohydrate.

Results: See table.