Independent factors associate with hospital mortality in patients with acute exacerbation of chronic obstructive pulmonary disease requiring intensive care unit admission: Focusing on the eosinophil-to-neutrophil ratio

Background Factors associated with hospital mortality are unclear in patients with acute exacerbation of COPD (AECOPD) requiring intensive care unit (ICU) admission. We aimed to characterize these patients and identify factors associated with hospital mortality. Patients and methods We used a retrospective observational case-control design and recruited patients between January 2015 and March 2017. Of 146 patients enrolled, 24 (16.4%) died during their hospital stay, while 122 survived. Results Multivariate logistic regression analyses revealed factors associated with hospital mortality: age (adjusted odds ratio [AOR] 1.12, 95% CI: 1.03-1.23), C-reactive protein (CRP) level >7.5 mg/dL at the emergency room (AOR 4.52, 95% CI: 1.27-16.04), peak eosinophil-to-neutrophil ratio (ENR) x10(2) on days 8-14 of treatment (AOR 0.22, 95% CI: 0.08-0.63), and in-hospital complications (AOR 4.23, 95% CI: 1.12-15.98) (all P<0.05). After receiver operating characteristic curve analyses, cutoff level for peak ENRx10(2) was 0.224. To examine the synergistic effects of CRP level and peak ENR, we divided patients into four groups: (G0, reference group) Peak ENRx10(2) >0.224 on days 8-14 and initial CRP <7.5 mg/dL; (G1) Peak ENRx10(2) >0.224 on days 8-14 and initial CRP >7.5 mg/dL; (G2) Peak ENRx10(2) <0.224 on days 8-14 and initial CRP <7.5 mg/dL; and (G3) Peak ENRx10(2) <0.224 on days 8-14 and initial CRP >7.5 mg/dL. For G2 and G3 patients, the AOR of mortality was significantly different from that of the reference group (G2: AOR 10.00, P = 0.020; G3: AOR 61.79, P<0.001). The relationship between 28-day mortality and the four groups was statistically significant (log-rank test, P<0.001). Conclusion Older age, initial CRP >7.5 mg/dL, peak ENR on days 8-14, and in-hospital complications were associated with hospital mortality in patients with AECOPD requiring ICU admission. Patients with both biomarkers, initial CRP >7.5 mg/dL, and peak ENRx10(2) <0.224 on days 8-14 of treatment, had an increased risk of hospital mortality.