Red blood cell distribution width and mortality in chronic obstructive pulmonary disease patients with acute respiratory failure: a retrospective study

To assess the association between red blood cell distribution width (RDW) levels and mortality in chronic obstructive pulmonary disease (COPD) patients with acute respiratory failure (ARF). We included patients with COPD admitted to the intensive care unit (ICU) across 208 U.S. hospitals between 2014 and 2015. The primary outcomes were ICU and in-hospital mortality. We employed univariable and multivariable logistic regression models to assess the association between RDW and mortality outcomes in COPD patients with ARF. To evaluate potential non-linear relationships, we utilized a generalized additive model (GAM) with smooth curve fitting. Additionally, a two-piecewise linear regression model was applied to identify the inflection point of RDW in relation to mortality risk. Sensitivity analyses were conducted to validate the robustness and reliability of the findings. This study included a total of 3,489 patients, with a mean age of 68.01 ± 11.29 years, of whom 1,669 (47.92%) were male. The RDW ranged from 11.40 to 29.20%, with a median value of 15.10%. The ICU mortality rate was 9.2%, while the in-hospital mortality rate was 15.28%. After adjusting for confounding factors, RDW was positively associated with the risk of ICU mortality in COPD patients with ARF (OR 1.08, 95% CI 1.03-1.14), and it was also positively associated with the risk of in-hospital mortality (OR 1.08, 95% CI 1.04-1.13). Furthermore, we observed a nonlinear relationship between RDW and ICU mortality risk, with a threshold effect. However, we did not find a nonlinear relationship between RDW and in-hospital mortality. Sensitivity and subgroup analyses confirmed the robustness of the relationship between RDW and mortality in COPD patients with ARF. RDW is positively correlated with both ICU mortality and in-hospital mortality in COPD patients with ARF. A nonlinear association was noted between RDW and ICU mortality, whereas a linear association was observed with in-hospital mortality. Further research is needed to investigate the mechanisms underlying these associations and to assess RDW's potential as a prognostic marker for critically ill COPD patients.