- Briefly, patients are laying down in a supine position on a bed during ongoing measure of ~30 min (see Figure 1) by connecting the calorimeter to the endotracheal tube (invasive mechanical ventilation) or to the facemask (non-invasive mechanical ventilation), or by using a transparent canopy in plexiglas to cover the head while room-air flows through and is mixed with the expirate (spontaneous breathing). This mixture of patient breath and room air is finally collected and analyzed by the IC device for O2 and CO2 concentrations, and used to calculate EE. The first 2 min of data is eliminated as acclimatization artefact. From the remaining ~28 min, a segment of 5 consecutive 1-min measures with 5% coefficient of variation in VO2 and VCO2 is considered as steady state.