The Prognostic Value of PaCO2 on the Response to Noninvasive Ventilation in Patients with AECOPD Complicated by Type II Respiratory Failure

Abstract

Background Acute exacerbation of chronic obstructive pulmonary disease (AECOPD) complicated by Type II respiratory failure frequently requires noninvasive ventilation (NIV). However, 10–25% of patients fail NIV and require intubation. The optimal timing and threshold of partial pressure of arterial carbon dioxide (PaCO2) for predicting NIV failure remain unclear. Methods In this two-center retrospective cohort study of 676 patients with AECOPD and Type II respiratory failure treated with NIV between 2012 and 2025, we used multivariable logistic regression and restricted cubic spline (RCS) analysis (4 knots at the 5th, 35th, 65th, and 95th percentiles) to assess the dose-response relationship between 24-hour post-treatment PaCO2 and NIV failure. Results NIV failure occurred in 73 patients (10.8%). After full adjustment for age, heart rate, white blood cell count, hemoglobin, albumin, blood urea nitrogen, D-dimer, and baseline HACOR score, each 1 mmHg increase in 24h PaCO2 was associated with 3% higher odds of NIV failure (OR 1.03, 95% CI 1.01–1.06). RCS analysis revealed a nonlinear L-shaped association (overall P < 0.001; nonlinear P < 0.01), with a threshold at 60.2 mmHg. Below this threshold, no significant association was observed; above it, odds increased markedly; this threshold requires further external validation in independent patient populations. After adjustment for confounding variables, the fully‑adjusted multivariable model yielded an AUC of 0.805 (95% CI 0.751–0.860). Conclusion A 24-hour post-treatment PaCO2 exceeding 60.2 mmHg identifies patients at high risk for NIV failure. This readily available bedside measure may guide escalation decisions in AECOPD with Type II respiratory failure.