A cross-sectional survey of nocturnal hypoxaemia in patients with Cryptogenic Fibrosing Alveolites (CFA)

Background: Two previous pilot studies (n=13 and n=11) have reported that a high proportion of patients with severe interstitial lung disease have nocturnal hypoxaemia. Since nocturnal hypoxaemia may cause symptoms, and is amenable to correction, we have surveyed nocturnal oxygenation in a representative sample of patients with CFA. Methods: We attempted to identify all patients with CFA attending Nottingham City Hospital using a combination of Lung Function records, in-patient records and local diagnostic databases. Cases were confirmed if our established diagnostic criteria were met and we included patients with connective tissue diseases. Nocturnal hypoxaemia was assessed at home using the Minolta Pulsox 31 system (Scientific Instruments, Oxford), and only continuous recordings of 5 hours or more were accepted for analysis. The Epworth sleepiness score, spirometry and resting daytime capillary blood gases were completed prior to each overnight study. Our main outcome measures were: mean SaO ₂ and the proportion of study time spent <90% SaO ₂. Results: Of 67 patients identified, 48 patients took part; 11 refused, 2 did not reply, 5 were too ill to come to hospital and one was on continuous oxygen treatment. There were 31 males (65%), the mean age was 68 years. Mean percent predicted FVC was 87% and mean PaO ₂ was 9.3kPa. Mean overnight SaO ₂ was 92.5% (95%CI 91.3 to 93.8) and the mean proportion of sleep time spent <90% SaO ₂ was 13.4% (95%CI 6.8 to 20.1). There were 21 patients who spent more than 2% of sleep time <90% SaO ₂ and these studies were designated abnormal. The Epworth score was higher for patients with abnormal studies (6.8 versus 10.7, p=0.002), and inversely correlated with mean overnight SaO ₂ (p=0.04). Conclusion: Nocturnal hypoxaemia is common in people with CFA and appears to be correlated with daytime sleepiness.