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Review
. 2021 Jan 12;9(1):8.
doi: 10.1186/s40560-021-00524-0.

Energy expenditure and indirect calorimetry in critical illness and convalescence: current evidence and practical considerations

Hanneke Pierre Franciscus Xaverius Moonen  1 , Karin Josephina Hubertina Beckers  1 , Arthur Raymond Hubert van Zanten  2   3
Affiliations
Review

Energy expenditure and indirect calorimetry in critical illness and convalescence: current evidence and practical considerations

Hanneke Pierre Franciscus Xaverius Moonen et al. J Intensive Care. .

Abstract

The use of indirect calorimetry is strongly recommended to guide nutrition therapy in critically ill patients, preventing the detrimental effects of under- and overfeeding. However, the course of energy expenditure is complex, and clinical studies on indirect calorimetry during critical illness and convalescence are scarce. Energy expenditure is influenced by many individual and iatrogenic factors and different metabolic phases of critical illness and convalescence. In the first days, energy production from endogenous sources appears to be increased due to a catabolic state and is likely near-sufficient to meet energy requirements. Full nutrition support in this phase may lead to overfeeding as exogenous nutrition cannot abolish this endogenous energy production, and mitochondria are unable to process the excess substrate. However, energy expenditure is reported to increase hereafter and is still shown to be elevated 3 weeks after ICU admission, when endogenous energy production is reduced, and exogenous nutrition support is indispensable. Indirect calorimetry is the gold standard for bedside calculation of energy expenditure. However, the superiority of IC-guided nutritional therapy has not yet been unequivocally proven in clinical trials and many practical aspects and pitfalls should be taken into account when measuring energy expenditure in critically ill patients. Furthermore, the contribution of endogenously produced energy cannot be measured. Nevertheless, routine use of indirect calorimetry to aid personalized nutrition has strong potential to improve nutritional status and consequently, the long-term outcome of critically ill patients.

Keywords: Critical illness; Energy expenditure (EE); Indirect calorimetry (IC); Intensive care unit (ICU); Metabolism; Resting energy expenditure (REE).

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Conflict of interest statement

Prof. Dr. Van Zanten reported having received honoraria for advisory board meetings, lectures, research, and travel expenses from Abbott, Baxter, BBraun, Cardinal Health, Danone-Nutricia, Fresenius Kabi, Mermaid, Lyric, and Nestlé-Novartis. Inclusion fees for patients in clinical trials were paid to the local ICU research foundation.

Figures

Fig. 1
Fig. 1
Components of energy expenditure
Fig. 2
Fig. 2
Progressing concepts of energy expenditure in critical illness. a Historical concept of energy expenditure in critical illness. b Current understanding of energy expenditure in critical illness and the contribution of various energy sources
Fig. 3
Fig. 3
Insertion of a disposable flowmeter into the patient circuit of a mechanic-ventilation system (QNRG®, Cosmed, Italy)
Fig. 4
Fig. 4
Use of a flow-dilution canopy hood to measure gas exchange in a spontaneously breathing patient (QNRG®, Cosmed, Italy)
See this image and copyright information in PMC

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