BACKGROUND:
The ratio of end-tidal CO2 pressure to arterial partial pressure of CO2 (
) 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
might be relevant in assessing ARDS not associated with COVID-19.
METHODS:
We evaluated the correspondence between
and the ratio of dead space to tidal volume (VD/VT) measured in 561 subjects with ARDS from a previous study in whom
data were also available. Subjects also were analyzed according to 4 ranges of
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:
correlated strongly with VD/VT (r = –0.87 [95% CI –0.89 to –0.85], P < .001). Decreasing
was associated with increased VD/VT and hospital mortality between all groups. In the univariate analysis, for every 0.01 decrease in
, mortality risk increased by ∼1% (odds ratio 0.009, 95% CI 0.003–0.029, P < .001) and maintained a strong independent association with mortality risk when adjusted for other variables (odds ratio 0.19, 95% CI 0.04–0.91, P = .039).
< 0.50 was characterized by very high mean ± SD value for VD/VT (0.82 ± 0.05, P < .001) and high hospital mortality (70%).
CONCLUSIONS:
Using
as a surrogate for VD/VT may be a useful and practical measurement for both management and ongoing research into the nature of ARDS.
