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(2)O; positive end-expiratory pressure: 3cmH(2)O) at FiO(2) of 21%, 50%, 85%, and 21% for 15 minutes at each FiO(2). Mean EE, oxygen consumption (VO2), and CO2 production (VCO2) 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 VCO2 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 VO2 and for VCO2 at 85% FiO(2). Conclusion Both systems measured EE, VO2, and VCO2 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).