Background & aims: The new indirect calorimeter developed in the framework of the ICALIC project was first evaluated in ventilation mode. This second phase aimed to compare its ease of use and precision with another commonly used device in spontaneously breathing adult patients using a canopy hood or a face mask.

Methods: The time required to measure resting energy expenditure (REE) with Q-NRG® in canopy and face mask mode was compared with Quark RMR® in canopy mode by sequential measurements in 45 and 40 spontaneously breathing adult patients, respectively. Their precision was assessed at different time intervals, using coefficients of variation (CV%) and repeated measures one-way ANOVA. Agreement between the two devices was evaluated by correlation coefficients, Bland-Altman plots, and paired t-test. Patients' characteristics potentially affecting the measurement were assessed using linear regression analysis.

Results: REE measurement with Q-NRG® was faster than Quark RMR® (19.7 ± 2.9 min vs 24.5 ± 4.3 min, P < 0.001). In canopy mode, Q-NRG® gave values similar to Quark RMR®, with 73% of patients achieving a steady state (CV% <10%) within the 5-15 min interval. In face mask mode, Q-NRG® was less stable than Quark RMR® in canopy mode, and steady state was achieved in only 40% of the patients within the 5-15 min interval. Correlation between the two devices was stronger when Q-NRG® was used in canopy than in face mask mode, with Pearson coefficients of 0.96 and 0.86, respectively. Compared to Quark RMR® in canopy mode, systematic bias±1.96∗SD with Q-NRG® was -14 ± 236 kcal/day in canopy and 73 ± 484 kcal/day in face mask mode. Q-NRG® in face mask mode overestimated REE by 150 ± 51 kcal/day in men compared to Quark RMR® in canopy mode.

Conclusions: Q-NRG® in canopy mode made it possible to save at least 5 min compared to Quark RMR® while maintaining the same measurement precision. However, its use in face mask mode could lead to REE overestimation in men and, therefore, should not be recommended in the clinical setting.

Trial registration: ClinicalTrials.gov no. NCT03947294.