End-tidal-to-arterial pco2 ratio as signifier for physiologic dead-space ratio and oxygenation dysfunction in acute respiratory distress syndrome

Abstract

BACKGROUND: The ratio of end-tidal CO2 pressure to arterial partial pressure of CO2 (PETCO2 /PaCO2 ) was recently suggested for monitoring pulmonary gas exchange in patients with ARDS associated with COVID-19, yet no evidence was offered supporting that claim. Therefore, we evaluated whether PETCO2 /PaCO2 might be relevant in assessing ARDS not associated with COVID-19. METHODS: We evaluated the correspondence between PETCO2 /PaCO2 and the ratio of dead space to tidal volume (VD/VT) measured in 561 subjects with ARDS from a previous study in whom PETCO2 data were also available. Subjects also were analyzed according to 4 ranges of PETCO2 /PaCO2 representing increasing illness severity (≥ 0.80, 0.6–0.79, 0.50–0.59, and < 0.50). Correlation was assessed by either Pearson or Spearman tests, grouped comparisons were assessed using either ANOVA or Kruskal-Wallis tests and dichotomous variables assessed by Fisher Exact tests. Normally distributed data are presented as mean and standard deviation(SD) and non-normal data are presented as median and inter-quartile range (IQR). Overall mortality risk was assessed with multivariate logistic regression. Alpha was set at 0.05. RESULTS: PETCO2 /PaCO2 correlated strongly with VD/VT (r = –0.87 [95% CI –0.89 to –0.85], P < 0.50 was characterized by very high mean ± SD value for VD/VT (0.82 ± 0.05, P