B79-01 Nocturnal and Exertional Hypoxaemia and Quantifying the Hypoxic Burden in Fibrotic Interstitial Lung Disease: Baseline Observations From a Multicentre Clinical Study

Abstract Prolonged hypoxaemia is associated with adverse outcomes in interstitial lung disease (ILD) with long-term oxygen therapy prescribed largely on evidence extrapolated from chronic obstructive pulmonary disease (COPD). Data supporting ambulatory oxygen therapy (AOT) in ILD are limited, showing improvements in health-related quality of life (HRQoL) but no consistent benefit in exercise capacity or survival. Nocturnal desaturation is associated with a greater deterioration in HRQoL and increased mortality, yet evidence for nocturnal oxygen prescription remains sparse. This study aims to determine whether nocturnal and exertional hypoxaemia predict functional decline in fibrotic ILD, as measured by six-minute walk test (6MWT), using hypoxic burden metrics that integrate both the depth and duration of desaturation alongside conventional physiological measures. We report baseline data from 160 participants in a multicentre observational study. Eligibility required a multidisciplinary diagnosis of fibrotic ILD with ≥10% fibrosis on CT, the ability to complete a 6-minute walk test (6MWT) and no resting oxygen requirement. Baseline assessments included lung function testing, 6MWT, blood biomarkers, and HRQoL questionnaires, repeated at planned follow-up at 6 and 12 months. Diagnoses include idiopathic pulmonary fibrosis (IPF, n = 40), systemic autoimmune rheumatic disease-associated ILD (SARD-ILD, n = 39), hypersensitivity pneumonitis (HP, n = 27), idiopathic non-specific interstitial pneumonitis (NSIP, n = 15), and sarcoidosis (n = 14). Participants with IPF and idiopathic NSIP are older and predominantly male, whereas those with HP, SARD-ILD, and sarcoidosis are significantly younger and predominantly female. Forced vital capacity (FVC) was lower in HP than IPF. Apparentdifferences in 6-minute walk distance (6MWD) by radiological pattern were lostafter multiple comparison testing. Otherwise no significant differences betweenILD diagnosis, radiological pattern, FVC, transfer factor for carbon monoxide(TLCO), 6MWD, or nocturnal hypoxic burden (measured as area below pre-eventbaseline and 90% saturation) were seen. Hypoxic burden below pre-event baseline correlated poorly with FVC %predicted (r = -0.086), TLCO %predicted (r = 0.030), 6MWD (r = 0.121) and time spent under 90% (T 90%) (r = 0.286), but strongly with 4% oxygen desaturation index (4%ODI) (r = 0.912). Similarly, hypoxic burden below 90% correlated weakly with FVC (r = -0.195), TLCO (r = -0.222), 6MWD (r = -0.289) and 4%ODI (r = 0.270), with strong correlation to T 90% (r = 0.952). Baseline data demonstrate significant age and sex variation between ILD subtypes with no significant physiological variation observed. Follow up data from this study will help determine whether nocturnal and exertional hypoxaemia, including hypoxic burden formulations, can better predict functional decline in fibrotic ILD. This abstract is funded by: None