Energy expenditure and caloric targets during continuous renal replacement therapy under regional citrate anticoagulation. A viewpoint

Abstract

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 CO 2 production (VCO 2 ) and O 2 consumption to calculate resting energy expenditure (REE) with the Weir equation. VCO 2 measurements are influenced by CRRT because CO 2 is exchanged during the blood purification process. CO 2 exchange also depends on type of pre-and/or postdilution fluid(s). CO 2 dissolves in different forms with dynamic but unpredictable impact on VCO 2 . 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.

MECCIAS trial: Metabolic consequences of continuous veno-venous hemofiltration on indirect calorimetry

“…The pathways to metabolize the excess of exogenous added citrate and resulting metabolites in the Krebs cycle could cost energy which may explain the increased REE during citrate predilution compared to saline predilution. Then, it is probably not used as a source of energy [15]. This is in contrast with current opinions that citrate should be added towards the non-intentional calories and deducted from the targeted caloric support [14].…”

“…CVVH has an impact on true REE, true V_CO 2 and V_O 2 as all these variables were lower without CVVH although the latter did not reach a statistically significant difference. The pathways advocated to alter REE during CVVH are metabolic impact of citrate [15] and the dialytrauma concept with immunologic activation and heat loss [13]. The dialytrauma concept [15] seems to have little impact on REE as there is little difference in REE between CVVH without citrate predilution and without CVVH.…”

“…The pathways advocated to alter REE during CVVH are metabolic impact of citrate [15] and the dialytrauma concept with immunologic activation and heat loss [13]. The dialytrauma concept [15] seems to have little impact on REE as there is little difference in REE between CVVH without citrate predilution and without CVVH. Development of CVVH filter technology have shown indeed to even remove cytokine production and immunologic reactions compared to earlier generations of filters [15,27].…”

“…The dialytrauma concept [15] seems to have little impact on REE as there is little difference in REE between CVVH without citrate predilution and without CVVH. Development of CVVH filter technology have shown indeed to even remove cytokine production and immunologic reactions compared to earlier generations of filters [15,27]. This confirms previously reported findings where no statistically significant difference in REE was found during intermittent hemodialysis with heparin [12].…”

“…CRRT-induces "dialytrauma" [13] which may alter metabolism. Citrate, the preferred anticoagulant for CRRT [14)], has direct impact on the patient's metabolism through interaction with the Krebs cycle [15,16].…”