An overnight increase in CO2 predicts mortality in sleep disordered breathing
Article first published online: 29 JUL 2012
© 2012 The Authors. Respirology © 2012 Asian Pacific Society of Respirology
Volume 17, Issue 6, pages 933–939, August 2012
How to Cite
BRILLANTE, R., LAKS, L., COSSA, G., PETERS, M. and LIU, P. (2012), An overnight increase in CO2 predicts mortality in sleep disordered breathing. Respirology, 17: 933–939. doi: 10.1111/j.1440-1843.2012.02209.x
- Issue published online: 29 JUL 2012
- Article first published online: 29 JUL 2012
- Accepted manuscript online: 5 JUN 2012 09:01AM EST
- Received 23 June 2011; invited to revise 5 January 2012; revised 30 January 2012; accepted 5 March 2012 (Associate Editor: David Hui).
- gas exchange;
- sleep disordered breathing
Background and objective: Sleep disordered breathing (SDB) is highly prevalent but under-recognized. Evidence is accumulating for its role as a predictor of mortality independent of cardiovascular risk factors. The role of hypercapnia in SDB is not known systematically, and between 11 and 43% of patients with SDB develop chronic hypercapnia. Hypercapnia predicts mortality in other respiratory conditions. The role of hypercapnia in independently predicting mortality in patients with SDB after assessing for the presence of airways disease and obesity was investigated.
Methods: The records of 396 consecutive patients were examined retrospectively. Univariate and multivariate analyses were performed using Cox proportional hazards regression to determine the association between gas exchange and polysomnography (PSG) variables and all-cause mortality, adjusted for potential confounders, including age, gender and presence of co-morbidity and airways disease.
Results: The mean age of our patient population was 55 ± 15 years, and the mean body mass index (BMI) was 30.6 ± 6.2 kg/m2. Out of the 322 patient population, 258 were men. After 10 years, 25% had died, following a maximum follow-up of 16.7 years. Mortality among patients with SDB was predicted by a difference between evening and morning PaCO2 (ΔPaCO2) of ≥7 mm Hg and evening hypoxaemia (PaO2 < 65 mm Hg), independent of age and the presence of co-morbidity and airways disease. There was a significant correlation between minimum oxygen saturation (SpO2) and ΔPaCO2 ≥ 7 mm Hg (P = 0.002) and evening PaO2 < 65 mm Hg (P < 0.001).
Conclusions: An overnight increase in CO2 and evening hypoxaemia are independent mortality predictors in SDB. A low minimum SpO2 identifies patients in whom morning and evening arterial blood gases are beneficial.