Indirect calorimetry: best results with close monitoring of the carbon dioxide fraction in exhaled air

Purpose: This study describes methods to improve resting energy expenditure (REE) estimated by the indirect calorimetry by evaluating predictors for the achievement of steady-state conditions (SSC). Methods: Cross-sectional study carried out with 20 women (30.2 ± 4.1 years; 27.8 ± 6.7 kg/m2). Indirect calorimetry was performed with the Quark RMR® calorimeter, during a 15-min period. VO2 consumption and VCO2 production were measured and data was collected every 5 s. Specific spreadsheet was used to compute the values of Steady REE and Software REE (deltaREE). Bias and concordance between values were assessed by the Bland-Altman plot and Lin’s correlation coefficient. Results: There is an almost perfect concordance between Software REE and Steady REE (p = 0.001). Steady% was important for predicting deltaREE while variation of carbon dioxide exhaled (CVFECO2) was significant to predict Steady%. Also, CVFECO2 was strongly and significantly correlated with the CV of VO2 (r = 0.83, p = 0001) and with the CV of VCO2 (r = 0.9, p = 0001). Conclusion: FECO2 should be sustained without huge variations to ensure SSC when using a calorimeter based on the canopy dilution technique with spontaneous breathing patients of similar characteristics. Also, these results suggest that since SSC occurs at least one time in the test, the Software REE may be considered reliable. © 2020, Springer Nature Switzerland AG.