An overnight increase in CO2 predicts mortality in sleep disordered breathing.
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.
Department of Thoracic and Sleep Medicine, Concord Hospital, New South Wales, Australia. robert.ruby@bigpond.com
Ruby
R
Brillante
Leon
L
Laks
Gavina
G
Cossa
Matthew
M
Peters
Peter
P
Liu
D000328:Adult; D000368:Aged; D002245:Carbon Dioxide / Q000097:blood; D002423:Cause of Death; D015897:Comorbidity; D005260:Female; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000453:epidemiology*; D000860:Hypoxia / Q000097:blood / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D050177:Overweight / Q000453:epidemiology; D017286:Polysomnography; D015995:Prevalence; D011659:Pulmonary Gas Exchange / Q000502:physiology; D012140:Respiratory Tract Diseases; D012189:Retrospective Studies; D012307:Risk Factors; D012891:Sleep Apnea Syndromes / Q000401:mortality*
D002245:Carbon Dioxide