• Yewon Chung, Frances L Garden, Adelle S Jee, Subash Srikantha, Saurabh Gupta, Peter R Buchanan, Peter W Collett, Guy B Marks, and Hima Vedam.
• Department of Respiratory and Sleep Medicine, Liverpool Hospital, Sydney, New South Wales, Australia.
• Intern Med J. 2017 Oct 1; 47 (10): 1136-1141.

BackgroundEvidence-based screening tools are required for detection of daytime hypercapnia in high-risk patient populations.AimsTo determine the validity of supine awake oximetry as a test for daytime hypercapnia and severe sleep disordered breathing (SDB) in super-obese patients.MethodsThis was a cross-sectional diagnostic test evaluation of super-obese adults (body mass index >50 kg/m2 ) presenting to Liverpool Hospital, Australia, between 2009 and 2015 for diagnostic polysomnography (PSG) and arterial blood gas measurement. Supine awake oxygen saturation (SpO2 ) was determined using oximetry measurements from the first three awake epochs of raw PSG data. Sensitivity and specificity of SpO2 for detecting patients with daytime hypercapnia (PaCO2 >45 mmHg) and severe SDB (respiratory disturbance index (RDI) >30 events/h) were assessed at various cut-off points and displayed using a receiver operating characteristic (ROC) curve. Area under the ROC curve and positive and negative predictive values (PPV and NPV) in the present patient population were derived.ResultsOf 52 patients, 23 (44%) had daytime hypercapnia. SpO2 measured awake in the supine position was associated with the presence of daytime hypercapnia but not with the presence of severe SDB. Overall, awake supine SpO2 <91.2% had 34.8% sensitivity, 96.6% specificity and 88.8% PPV, and SpO2 <96.7% had 87.0% sensitivity, 20.7% specificity and 66.7% NPV for the presence of daytime hypercapnia.ConclusionAwake supine oximetry is an easily performed test that may have novel use in identifying patients at high risk of respiratory failure. Future studies are required to evaluate prospectively its role in screening patients at risk of daytime hypercapnia.© 2017 Royal Australasian College of Physicians.

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