Applied Comparison of Mindray metabolic system and the GE S/5 metabolic system: Indirect calorimetry in critically ill, mechanically ventilated patients

Objective: Indirect calorimetry is the recommended, most accurate way to measure resting energy expenditure (REE) in critically ill, mechanically ventilated patients. We tested the agreement of two systems: the Mindray metabolic system (the system to be validated) and the GE S/5 metabolic system (the reference system). We also compared the measurements obtained to commonly used predictive equations. Methods: This was a prospective single-center study, in a general 16-bed intensive care unit, with critically ill, mechanically ventilated patients eligible to undergo indirect calorimetry. REE was measured successively during the same session with two 30-min measurements. The agreement and bias between oxygen consumption, carbon dioxide production, REE, and respiratory quotient obtained by Mindray and GE systems were compared using Bland-Altman plots. A priori we defined an acceptable within-method error to be 20% or less and an acceptable between-methods error to be 30% or less, according to Critchley and Critchley. Results: Forty measurements were performed with 16 participants. All measurements were included in the final analysis. The mean REE was 2478 ± 650 kcal/d for the GE system and 2166 ± 415 kcal/d for the Mindray system (P ˂ 0.0001), for a difference of 12.6%. This difference in REE is related to the variations between the two devices in both oxygen consumption and carbon dioxide production. Conclusions: The Mindray metabolic system, compared to the GE S/5 metabolic system (the reference method used), measured REE with a mean difference of 12.6%. The Mindray-measured REE was within an error limit we defined a priori.