We followed with interest the discussion [1, 2] fueled by the study of Stapel et al. [3] who reported fairly accurate assessment of energy expenditure (EE) in critically ill patients based on ventilator-derived carbon dioxide production (VCO2). The proposed technique is elegant and valid but has inherent limitations. It is applicable in patients who are in one way or another ventilator-dependent but not in spontaneously breathing yet oxygen-dependent subjects. We concur that VO2 is the most relevant variable for EE measurement. However, the most accurate and precise estimation of EE in a critically ill population can only be obtained by sampling of inspired and expired oxygen/carbon dioxide concentrations and measuring expired gas flow. This is the core task of indirect calorimetry [4].
Initiative has been undertaken to develop a ‘full option’, easy-to-use, accurate, and affordable indirect calorimeter. The project is supported by the European Society of Intensive Care Medicine and the European Society of Parenteral and Enteral Nutrition [5] and has actually reached Technology Readiness Level. It is probably only a matter of time before such a device will render all current mathematical uproar obsolete.
Abbreviations
- EE:
-
Energy expenditure
- VCO2 :
-
Carbon dioxide production
References
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See related research by Stapel et al. http://ccforum.biomedcentral.com/articles/10.1186/s13054-015-1087-2
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De Waele, E., Honoré, P.M. & Spapen, H.D. VCO2 calorimetry: stop tossing stones, it’s time for building!. Crit Care 20, 399 (2016). https://doi.org/10.1186/s13054-016-1575-z
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DOI: https://doi.org/10.1186/s13054-016-1575-z