Defining a CT phenotype of severe COPD patients who develop hypercapnia

Background: Chronic hypercapnic respiratory failure (CHRF) is common in patients with severe COPD. However, not all patients become hypercapnic. A better understanding of the underlying pathophysiology contributing to the development of CHRF in COPD is needed. Aims: To explore a CT phenotype which can be linked to hypercapnic COPD patients. Methods: 909 COPD patients from 2 previously established COPD cohorts were included (NCT04023409 + NCT03053973). Patients were grouped as normocapnic (PaCO2 <6kPa) or hypercapnic (PaCO2 ≥6kPa). Quantitative assessment of the CT-scans allowed for the distinction between different CT phenotypes, based on air trapping-, emphysema-, and airway pathology parameters. Results: Expiratory lung volume, emphysema- and air trapping scores were similar in both groups (table 1). Pi10 on the other hand, a measure of airway wall thickness, was found to be significantly higher in the hypercapnic patients. The correlation between Pi10 and PaCO2 was also significant (p=0.001). Conclusions: It appears that a higher average airway wall thickness is associated with the presence of hypercapnia in COPD, while scores related to emphysema were not. This might imply that predominant airway disease might predispose to chronic hypercapnia. Future research is needed to investigate whether selection of patients for therapeutic options, such as chronic non-invasive ventilation, might be improved by including CT phenotyping. Table1. CT parameters in normocapnic and hypercapnic COPD patients.