RESUMO
BACKGROUND: Indirect calorimetry (IC) is the gold standard for measuring energy expenditure in critically ill patients However, continuous renal replacement therapy (CRRT) is a formal contraindication for IC use. AIMS: To discuss specific issues that hamper or preclude an IC-based assessment of energy expenditure and correct caloric prescription in CRRT-treated patients. METHODS: Narrative review of current literature. RESULTS: Several relevant pitfalls for validation of IC during CRRT were identified. First, IC measures CO2 production (VCO2) and O2 consumption to calculate resting energy expenditure (REE) with the Weir equation. VCO2 measurements are influenced by CRRT because CO2 is exchanged during the blood purification process. CO2 exchange also depends on type of pre- and/or postdilution fluid(s). CO2 dissolves in different forms with dynamic but unpredictable impact on VCO2. Second, the effect of immunologic activation and heat loss on REE caused by extracorporeal circulation during CRRT is poorly documented. Third, caloric prescription should be adapted to CRRT-induced in- and efflux of different nutrients. Finally, citrate, which is the preferred anticoagulant for CRRT, is a caloric source that may influence IC measurements and REE. CONCLUSION: Better understanding of CRRT-related processes is needed to assess REE and provide individualized nutritional therapy in this condition.
