Noninvasive Surrogate for Physiologic Dead Space Using the Carbon Dioxide Ventilatory Equivalent: Testing in a Single-Center Cohort, 2017–2023

We sought to evaluate the association between the carbon dioxide ( co2 ) ventilatory equivalent (VEq co2 = minute ventilation/volume of co2 produced per min), a marker of dead space that does not require a blood gas measurement, and mortality risk. We compared the strength of this association to that of physiologic dead space fraction (V D /V t = Pa co2 -mixed-expired P co2 /Pa co2 ) as well as to other commonly used markers of dead space (i.e., the end-tidal alveolar dead space fraction AVDSf = (Pa co2 -end-tidal P co2 )/Pa co2 , and ventilatory ratio VR = (minute ventilation × Pa co2 )/(age-adjusted predicted minute ventilation × 37.5)).