To investigate the clinical significance of the eosinophil-to-neutrophil ratio (ENR) in predicting the efficacy of noninvasive positive pressure ventilation (NIPPV) in elderly patients with acute exacerbation of chronic obstructive pulmonary disease (AECOPD).

A total of 146 elderly AECOPD patients who received NIPPV treatment in our hospital from January 2022 to January 2025 were enrolled. Twenty-six patients with NIPPV failure were assigned to the observation group and 120 with successful treatment to the control group. The changes in ENR, acute physiology and chronic health evaluation Ⅱ(APACHEⅡ) score, Charlson comorbidity index (CCI), and ROX index were compared between the two groups before NIPPV initiation (T₀), and at 2 hours (T₂), 6 hours (T₆), and 12 hours (T₁₂) after initiation. Spearman correlation analysis was used to assess the relationship between ENR and arterial blood gas parameters. Receiver operating characteristic (ROC) curves were employed to evaluate the predictive value of ENR for NIPPV efficacy. Multivariate logistic regression analysis was performed to identify influencing factors of NIPPV failure, and restricted cubic spline (RCS) analysis was applied to explore the dose-response relationship between ENR and NIPPV failure risk.

At T₀, eosinophil percentage [0.10% (0.00%, 0.62%) vs. 0.40% (0.00%, 1.50%)] and ENR [0.12×10^-2(0.00×10^-2, 0.79×10^-2) vs. 0.52×10^-2(0.00×10^-2, 2.33×10^-2)] in the observation group were lower than those in the control group (P<0.01). At T₂, eosinophil percentage [0.17% (0.00%, 0.68%) vs. 0.50% (0.10%, 1.50%)] and ENR [0.23×10^-2 (0.00×10^-2, 0.92×10^-2) vs. 0.58×10^-2 (0.11×10^-2, 2.33×10^-2)] remained lower in the observation group (P<0.01). No significant difference in ENR was observed between the two groups at T₆ and T₁₂ (P>0.05). At T₀, ENR was significantly positively correlated with PaO₂ (r=0.651, P<0.001), but not significantly correlated with pH, PaCO₂, or HCO₂^-. The area under the ROC curve (AUC) for T₀ ENR to predict NIPPV failure was 0.781 (95% CI: 0.705~0.845), with an optimal cutoff value of <0.350×10^-2, yielding a sensitivity of 84.62% and specificity of 88.33%. The AUC for T₂ ENR was 0.731 (95%CI: 0.651~0.801), with a cutoff value of <0.391×10^-2. Multivariate logistic regression showed that APACHE Ⅱ score ≥15(OR=1.148, P=0.003) and CCI ≥4 (OR=1.236, P=0.013) were risk factors for NIPPV failure, whereas T₀ ENR (OR=0.591, P=0.004) and ROX index (OR=0.783, P=0.002) were protective factors. RCS analysis indicated a nonlinear relationship between ENR and NIPPV failure risk (P for nonlinearity=0.0586). The combined model incorporating APACHE Ⅱ, CCI, ROX index, and T₀ ENR predicted NIPPV failure with an AUC of 0.907 (95%CI: 0.845~0.947, P<0.001), sensitivity of 84.62%, and specificity of 88.33%. During hospitalization, NIPPV failure occurred in 26 patients (17.81%); 10 patients (38.46%) in the observation group died in-hospital, while no deaths occurred in the control group.

ENR can predict the risk of NIPPV failure in AECOPD patients. A T₀ ENR<0.350×10^-2 before NIPPV initiation warrants cautious management.