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Introduction and ObjectivesObstructive sleep apnoea (OSA) is often undiagnosed and hence untreated. Its prevalence is ever increasing given the escalating obesity of the population. Apnoea/hypopnoea index (AHI) is commonly used to diagnose and classify the severity of OSA. The overnight oximetry, which measures oxygen desaturation index (ODI), is far simpler to measure than a full respiratory polysomnography, but its diagnostic accuracy at predicting OSA has not been formally established. We proposed that in patients with morbid obesity (BMI ≥40), the diagnostic accuracy for establishing an OSA diagnosis using ODI is as effective as AHI.MethodsThe data from the respiratory polysomnography of those individuals with a BMI greater than 40 kg/m2, who were referred between January to December 2015 to the sleep service at St Peter’s Hospital, were reviewed and measures of AHI and ODI were compared.Results79 individuals with a BMI greater than 40 who underwent respiratory polysomnography were identified.Mean age 52 (Age range 21–78)Mean BMI 47.4 (BMI range 40–66.2)Mean AHI 36 (AHI range 2.7–112.1)Mean ODI 36.6 (ODI range 3–105.5)For BMI’s≥40, ODI is as effective as AHI in diagnosing OSA with a strong positive correlation (R2=0.955). For those at the more severe end of the spectrum, the correlation is deeper.Abstract P62 Table 1Positive correlation for AHI and ODI at BMI>40DiscussionThe data provided by a respiratory polysomnography test provides a range of parameters, but polysomnography is resource intensive and requires significant time and expertise to assess properly. SIGN guidance states that oximetry can positively diagnose OSA but cannot exclude it.1 There are multiple benefits to having a simple tool that can identify high-risk individuals that may suffer with OSA including early diagnosis and reduced cost as well as resource utilisation. This is likely to improve patient care with earlier diagnosis and treatment of OSA. Overnight oximetry can safely diagnose OSA in morbidly obese patients. This has the potential to optimise efficiency and reduce cost without impacting patient care.ReferencesChung F, Liao P, Elsaid H, Islam S, Shapiro CM, Sun Y. Oxygen desaturation index from nocturnal oximetry: A sensitive and specific tool to detect sleep-disordered breathing in surgical patients. Anesth Analg2012;114(5):993–1000.SIGN. Management of obstructive sleep apnoea/hypopnoea syndrome in adults: a national clinical guideline. Scottish Intercollegiate Guidelines Network2003.

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