Alveolar Dead Space Fraction Discriminates Mortality in Pediatric Acute Respiratory Distress Syndrome

Objectives: Physiologic dead space is associated with mortality in acute respiratory distress syndrome, but its measurement is cumbersome. Alveolar dead space fraction relies on the difference between arterial and end-tidal carbon dioxide (alveolar dead space fraction = (PacoPetco₂)/Paco. We aimed to assess the relationship between alveolar dead space fraction and mortality in a cohort of children meeting criteria for acute respiratory distress syndrome (both the Berlin 2012 and the American-European Consensus Conference 1994 acute lung injury) and pediatric acute respiratory distress syndrome (as defined by the Pediatric Acute Lung Injury Consensus Conference in 2015). Design: Secondary analysis of a prospective, observational cohort. Setting: Tertiary care, university affiliated PICU. Patients: Invasively ventilated children with pediatric acute respiratory distress syndrome. Interventions: None. Measurements and Main Results: Of the 283 children with pediatric acute respiratory distress syndrome, 266 had available Petco₂. Alveolar dead space fraction was lower in survivors (median 0.13; interquartile range, 0.06-0.23) than nonsurvivors (0.31; 0.19-0.42; p < 0.001) at pediatric acute respiratory distress syndrome onset, but not 24 hours after (survivors 0.12 [0.06-0.18], nonsurvivors 0.14 [0.06-0.25], p = 0.430). Alveolar dead space fraction at pediatric acute respiratory distress syndrome onset discriminated mortality with an area under receiver operating characteristic curve of 0.76 (95% CI, 0.66-0.85; p < 0.001), better than either initial oxygenation index or PaoFio In multivariate analysis, alveolar dead space fraction at pediatric acute respiratory distress syndrome onset was independently associated with mortality, after adjustment for severity of illness, immunocompromised status, and organ failures. Conclusions: Alveolar dead space fraction at pediatric acute respiratory distress syndrome onset discriminates mortality and is independently associated with nonsurvival. Alveolar dead space fraction represents a single, useful, readily obtained clinical biomarker reflective of pulmonary and nonpulmonary variables associated with mortality.