Comparison of resting energy expenditure measured with metabolic cart and calculated with predictive formulas in critically ill patients on mechanical ventilation.

The purpose was to compare the resting energy expenditure (REE) measured with the Q-NRG™+ metabolic-cart (MREE) with REE predicted by equations (the Harris-Benedict formula and an equation developed in ward, REE-HB and REE-W, respectively). We also aimed to assess the agreement of the measurements of oxygen consumption ( V ̇ O 2 ) and carbon dioxide production ( V ̇ CO 2 ) at different inspired fractions of oxygen (FiO 2). 27 mechanically ventilated ICU patients were enrolled. V ̇ O 2 and V ̇ CO 2 were measured by Q-NRG™+ during breathing 40% and 60% FiO 2. MREE was compared with REE-W and REE-HB normalized for body weight. V ̇ O 2 was 233.0 (95.2) ml/min and 217.5 (89.8) ml/min at FiO 2 40% and 60%, respectively (NS). V ̇ CO 2 was 199.0 (91.7) ml/min at FiO 2 40%, and 197.5 (85.5) ml/min at FiO 2 60% (NS). The REE estimated from the equations was significantly different from the MREE. The best agreement was found for the Harris-Benedict equation without correction for stress-factors. Harris-Benedict equation corrected overestimates REE. This new metabolic cart Q-NRG™+ provides a concordance of values for V ̇ O 2 and V ̇ CO 2 when measured at different FiO 2 , and is a reliable tool for estimating energy expenditure and assessing the nutritional needs of the patient. This study demonstrates that the estimation of REE using predictive formulas does not allow accurate calculation of metabolic demands in ventilated intensive care patient. However, predictive equations allow for a rapid assessment of REE and calculation of the amount of energy derived from different substrates. • A new metabolic-cart was used to evaluate V ̇ O 2 and V ̇ CO 2 at different FiO 2 in ICU. • This new tool allows the measurement of REE in mechanically ventilated patients. • REE measured by metabolic cart and predicted by formulas have been compared. • REE by formulas does not allow accurate calculation of metabolic demands. [ABSTRACT FROM AUTHOR]