Indirect calorimetry in mechanically ventilated patients. A systematic comparison of three instruments

Abstract

Background & aims: Indirect calorimetry is the gold standard in determining energy expenditure to dose nutritional therapy for critically ill patients. The most commonly used system for indirect calorimetry in the ICU setting (Deltatrac Metabolic Monitor) is no longer in production. The aim of this study was to compare two new instruments for IC (Quark RMR, CCM Express) to the Deltatrac in mechanically ventilated patients.

Methods: Sequential measurements with all three instruments were performed in randomized order on 24 mechanically ventilated ICU patients. Resting energy expenditure (REE), respiratory quotient (RQ), oxygen consumption and carbon dioxide production were recorded during a stable 10-30 min period.

Results: There was no difference in mean REE measurements between Deltatrac, 1749 ± 389 kcal/24 h and Quark RMR, 1788 ± 494 kcal/24 h (P = 0.166). CCM Express produced 64% higher mean REE values (2876 ± 656 kcal/24 h) than Deltatrac (P < 0.0001). All instruments registered different values for RQ and expiratory minute volume.

Conclusion: Available instruments for indirect calorimetry give conflicting estimates of energy expenditure in mechanically ventilated patients. Whilst the Quark RMR compares better with the Deltatrac than CCM Express, the mechanisms behind this difference needs to be further explored.