Reliability of, and Agreement Between, two Breath-by-Breath Indirect Calorimeters at Varying Levels of Inspiratory Oxygen

Background: Indirect calorimetry (IC) is considered the accurate way of measuring energy expenditure (EE). IC devices often apply the Haldane transformation, introducing errors at inspiratory oxygen fraction (FiO ₂) >60%. The aim was to assess measurement reliability and agreement between an unevaluated IC (device 2) (Beacon Caresystem, Mermaid Care A/S, Noerresundby, Denmark) not using Haldane transformation and an IC that does (device 1) (Ecovx, GE, Helsinki, Finland) at varying FiO ₂. Methods: Twenty healthy male subjects participated, with 16 completing the study (33 ± 9 years, 83.3 ± 16 kg, 1.83 ± 0.08 m). Subjects were mechanically ventilated in pressure support (3cmH ₂O; positive end-expiratory pressure: 3cmH ₂O) at FiO ₂ of 21%, 50%, 85%, and 21% for 15 minutes at each FiO ₂. Mean EE, oxygen consumption (VO ₂), and CO ₂ production (VCO ₂) were compared within and between devices across FiO ₂ levels. Results: Device 2 showed within-device EE significant differences at 21% vs 50% FiO ₂ and device 1 for VCO ₂ at 50% vs. 85% FiO ₂. For all variables, both devices showed reliable measurements at 21% and 50% FiO ₂, but at 85%, FiO ₂ bias and limits of agreement increased. Between devices, there were significant differences for EE at both 21% and 85% FiO ₂ for VO ₂ and for VCO ₂ at 85% FiO ₂. Conclusion: Both systems measured EE, VO ₂, and VCO ₂ at 21%–85% FiO ₂ reliably but with bias at 85% FiO ₂. The devices were in agreement at 21% and 50% FiO ₂, but further studies need to confirm accuracy at high FiO ₂.