• Anoopindar K Bhalla, Margaret J Klein, Justin Hotz, Jeni Kwok, Jennifer E Bonilla-Cartagena, David A Baron, Kristen Kohler, Dinnel Bornstein, Daniel Chang, Kennedy Vu, Anabel Armenta-Quiroz, Lara P Nelson, NewthChristopher J LCJLDepartment of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, CA.Department of Pediatrics, Keck School of Medicine, University of Southern California, Los Angeles, CA., and Robinder G Khemani.
• Department of Anesthesiology and Critical Care Medicine, Children's Hospital Los Angeles, Los Angeles, CA.
• Pediatr Crit Care Me. 2024 Sep 1; 25 (9): 784794784-794.

ObjectivesWe 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)]).DesignRetrospective cohort data, 2017-2023.SettingQuaternary PICU.PatientsOne hundred thirty-one children with acute respiratory distress syndrome.InterventionsNone.Measurements And Main ResultsAll dead space markers were calculated at the same 1-minute timepoint for each patient within the first 72 hours of using invasive mechanical ventilation. The 131 children had a median (interquartile range, IQR) age of 5.8 (IQR 1.4, 12.6) years, oxygenation index (OI) of 7.5 (IQR 4.6, 14.3), V D /V t of 0.47 (IQR 0.38, 0.61), and mortality was 17.6% (23/131). Higher VEq co2 ( p = 0.003), V D /V t ( p = 0.002), and VR ( p = 0.013) were all associated with greater odds of mortality in multivariable models adjusting for OI, immunosuppressive comorbidity, and overall severity of illness. We failed to identify an association between AVDSf and mortality in the multivariable modeling. Similarly, we also failed to identify an association between OI and mortality after controlling for any dead space marker in the modeling. For the 28-day ventilator-free days outcome, we failed to identify an association between V D /V t and the dead space markers in multivariable modeling, although OI was significant.ConclusionsVEq co2 performs similarly to V D /V t and other surrogate dead space markers, is independently associated with mortality risk, and may be a reasonable noninvasive surrogate for V D /V t .Copyright © 2024 by the Society of Critical Care Medicine and the World Federation of Pediatric Intensive and Critical Care Societies.

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