Supine awake oximetry as a screening tool for daytime hypercapnia in super-obese patients

Evidence-based screening tools are required for detection of daytime hypercapnia in high-risk patient populations.

To determine the validity of supine awake oximetry as a test for daytime hypercapnia and severe sleep disordered breathing (SDB) in super-obese patients.

This 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.

Of 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.

Awake 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.