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COPD–OSAHS overlap syndrome — SCE Respiratory MCQ

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HardContinuous Positive Airway PressureCOPD–OSAHS overlap syndromeSCE Respiratory

A 67-year-old man with smoking-related COPD reports loud snoring, witnessed apnoeas, morning headache and sleepiness while driving. His COPD is clinically stable on optimised inhaled therapy, with no exacerbation for 4 months. His BMI is 27 kg/m², and he takes no opioids or sedatives. Post-bronchodilator FEV1 is 43% predicted. An awake arterial blood gas on air shows pH 7.38, PaCO2 6.9 kPa and PaO2 8.4 kPa. He does not meet criteria for long-term oxygen therapy. Respiratory polygraphy shows an apnoea–hypopnoea index of 52 events/hour, comprising predominantly obstructive events, with an oxygen desaturation index of 54 events/hour. Oxygen saturation is below 90% for 34% of the recording, with a nadir of 78%. Transcutaneous CO2 remains between 6.7 and 6.9 kPa throughout sleep, without a sustained sleep-related rise. Which initial nocturnal respiratory-support plan is most appropriate?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: E — Commence nocturnal CPAP; reassess gas exchange and add oxygen only if hypoxaemia persists after optimisation.

Explanation lettering: D = shown as A · C = shown as B · A = shown as C · E = shown as D · B = shown as E

This is COPD–OSAHS overlap syndrome with severe, predominantly obstructive sleep-disordered breathing. Although he has mild awake hypercapnia, his PaCO2 is 6.9 kPa and therefore does not exceed the NICE severe-hypercapnia threshold of 7.0 kPa. Moreover, transcutaneous monitoring shows no sustained nocturnal CO2 rise to indicate nocturnal hypoventilation. CPAP is therefore the appropriate initial ventilatory modality. The substantial nocturnal hypoxaemia does not justify adding oxygen at initiation. Much of it may result from recurrent upper-airway obstruction, and NICE recommends optimising control of apnoea and nocturnal hypoventilation with CPAP or non-invasive ventilation before adding oxygen. Oxygen should be considered if clinically important hypoxaemia persists after PAP optimisation and other causes have been addressed. A is inappropriate because modest stable hypercapnia at or below 7.0 kPa, without nocturnal hypoventilation, does not establish a need for non-invasive ventilation. C introduces oxygen before determining the response to CPAP. D combines two premature escalations: non-invasive ventilation despite the absence of severe hypercapnia or nocturnal hypoventilation, and oxygen before PAP optimisation. E may improve saturation but does not treat the severe obstructive events, sleep fragmentation or associated safety-critical sleepiness; oxygen alone can also obscure the desaturation signal without correcting upper-airway obstruction.

Reference: NG202, section 3: COPD–OSAHS overlap syndrome (Published 20 August 2021; checked 18 August 2026) — https://www.nice.org.uk/guidance/ng202/chapter/3-COPDOSAHS-overlap-syndrome NG202, recommendations 3.5.5 and 3.7.6 (Published 20 August 2021; checked 18 August 2026) — https://www.nice.org.uk/guidance/ng202/chapter/3-COPDOSAHS-overlap-syndrome