Energy expenditure and substrate utilization in mechanically ventilated children

The objective of the study was to determine the value of indirect calorimet ry and nitrogen balance (N balance) in order to evaluate the current feedin g protocols of mechanically ventilated children. The study was designed as a cross-sectional prospective study. in 36 mechanically ventilated children energy expenditure was measured by indirect calorimetry, and total urinary nitrogen excretion (TUN) was determined. Substrate utilization and respira tory quotient (RQ) were calculated from the measured values of oxygen consu mption (Vo(2)), carbon dioxide production (Vco(2)), and TUN. The RQ was com pared with the RQ of the macronutrients administered (RQmacr) according to the modified criteria of Lusk. In results, the total measured energy expend iture (TMEE) showed a wide variation (range 155-272 kJ.kg(-1).d(-1)). The N balance was positive in 20 and negative in 16 patients. The ratio of calor ic intake/TMEE was significantly higher in patients with a positive N balan ce (1.50 +/- 0.06) as compared with those with a negative N balance (0.8 +/ - 0.1, P < 0.001). There was a significant relationship between the differe nce of RQ - RQmacr versus the ratio caloric intake/TMEE (r = 0.72, P < 0.00 1). Carbohydrate and fat utilization were not significantly different in pa tients with a positive or negative N balance. Protein utilization was signi ficantly higher in those patients with a negative N balance. We concluded t hat measurement of TMEE with indirect calorimetry results in accurate deter mination of energy needs in critically ill mechanically ventilated children . Feeding according to or in excess of the TMEE is correlated with a positi ve N balance. A combination of the RQ and the RQmacr can be helpful in diff erentiating under- or overfeeding. (C) Elsevier Science Inc. 1999.