Hypoxemia severity and survival in ILD and COPD on long-term oxygen therapy : The population-based DISCOVERY study

BACKGROUND AND AIM: Whether long-term oxygen therapy (LTOT) improves survival in interstitial lung disease (ILD) is unclear. A recent study reported similar survival in ILD patients with severe hypoxemia on LTOT vs. moderate hypoxemia without LTOT, and proposed that LTOT could be indicated in ILD already at moderate hypoxemia. The aim of this study was to compare survival by severity of hypoxemia in patients with ILD and COPD, respectively, treated with LTOT. METHODS: A population-based, longitudinal study of adults starting LTOT for ILD or COPD 1987-2018. Transplant-free survival was compared between moderate (PaO2 7.4-8.7 kPa) and severe (PaO2<7.4 kPa) hypoxemia using Cox regression, adjusted for age, sex, BMI, smoking status, WHO performance status, year of starting LTOT, diagnosis of heart failure, ischemic heart disease and diabetes mellitus. RESULTS: In total, 17,084 patients were included, with ILD and moderate (n = 470) or severe hypoxemia (n = 2,408), and COPD with moderate (n = 2,087) or severe hypoxemia (n = 12,119). Compared with in COPD, ILD patients on LTOT had lower transplant-free survival after one year (41.9 vs. 67.1%) and two years (20.3 vs. 46.5%). In COPD worse hypoxemia was associated with slightly increased risk of death/lung transplantation, aHR 1.07 (1.00-1.14), a difference not shown in ILD, aHR 0.91 (0.80-1.03). CONCLUSION: Transplant-free survival did not differ in ILD patients between moderate and severe hypoxia despite LTOT