Actual energy expenditure in patients on extracorporeal membrane oxygenation: a modified indirect calorimetry vs. traditional approaches

Patients on extracorporeal membrane oxygenation (ECMO) are the most severe in ICUs and require complex treatment. Nutritional support (NS) is a vital component of critical care. Indirect calorimetry (IC) is the gold standard for bedside assessment of actual energy expenditure (AEE) in the ICU. However, two “gas exchange points” require monitoring of oxygen consumption and carbon dioxide elimination from lungs and membrane oxygenator. This significantly limits the capabilities of modern IC devices. We developed an original method for estimation of AEE in ECMO patients enabling synchronous gas analysis. Objective. To compare AEE values obtained using a modified indirect calorimetry, predictive equations and empirical approaches in patients on veno-arterial ECMO. Material and methods. A single-center prospective open cohort study included 15 patients on veno-arterial ECMO. AEE was assessed using a modified IC method based on simultaneous measurement of oxygen consumption and carbon dioxide excretion from lungs (via metabolic monitor) and membrane oxygenator (via pneumatic flowmeter and portable capnograph). These data were used to calculate AEE using the J.B. Weir equation. AEE values were compared with empiric data on energy expenditure in accordance with the guidelines of the Federation of Anesthesiologists and Reanimatologists (25 kcal/kg/day) and basal metabolic rate (Harris-Benedict formula). Results. There were 15 measurements. Mean AEE was 2180 [1830—2446] kcal/day (29.2 [24.6—31.2] kcal/kg/day). These values significantly exceeded the recommended empirical value (25 kcal/kg/day, p=0.046) and the calculated BMR according to the Harris-Benedict formula (23.3 [20.5—25] kcal/kg/day, p<0.001). Conclusion. Indirect calorimetry is feasible in ECMO patients with appropriate equipment. Energy expenditure in these patients significantly exceeds the recommended 25 kcal/kg/day and the calculated basal metabolic rate. The effect of ECMO on energy metabolism in critically ill patients requires further research.