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Obesity hypoventilation syndrome — SCE Respiratory MCQ

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HardObesityObesity hypoventilation syndromeSCE Respiratory

A 52-year-old woman with a BMI of 51 kg/m² is reviewed after 4 months of treatment for obesity hypoventilation syndrome. At diagnosis, while clinically stable, her awake PaCO₂ was 7.5 kPa and respiratory polygraphy showed severe obstructive sleep apnoea–hypopnoea syndrome with an apnoea–hypopnoea index of 68 events/hour. Spirometry, chest radiography and thyroid function were normal, and she takes no respiratory-depressant medication. Fixed-level continuous positive airway pressure (CPAP) was started alongside a specialist weight-management programme. Her device download now shows use for 7.3 hours/night, minimal unintentional leak and a residual apnoea–hypopnoea index of 3 events/hour. Daytime sleepiness has improved, but morning headache and exertional breathlessness persist. Awake arterial blood gases on air show pH 7.38, PaCO₂ 7.2 kPa, PaO₂ 7.8 kPa and bicarbonate 33 mmol/L. Overnight monitoring while using CPAP shows sustained transcutaneous hypercapnia and oxygen saturation below 88% for 18% of the recording. Which respiratory treatment plan is most appropriate?

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

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Correct answer: A — Change from CPAP to nocturnal non-invasive ventilation, optimise it, then reassess the oxygen requirement

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

CPAP was an appropriate first-line treatment because she had stable obesity hypoventilation syndrome with severe OSAHS. However, adherence is objectively excellent, leak is minimal and the residual AHI is normal, demonstrating effective control of upper-airway obstruction. Persistent awake hypercapnia, symptoms and sustained nocturnal transcutaneous hypercapnia therefore represent residual hypoventilation despite effective CPAP. NICE recommends changing to non-invasive ventilation when hypercapnia persists during CPAP treatment. D is correct: NIV should be instituted and optimised before deciding whether oxygen remains necessary. A treats hypoxaemia without correcting the uncontrolled hypoventilation. B is inappropriate because obstructive events are already controlled; additional CPAP pressure does not provide pressure-supported ventilation. C is a plausible near-miss, but supplemental oxygen is considered when hypoxaemia persists despite optimal control of both nocturnal hypoventilation and AHI, rather than being added routinely when NIV starts. E correctly recognises the importance of weight management, but weight loss complements rather than replaces timely escalation of ventilatory support; delaying for 6 months leaves established ventilatory failure inadequately treated.

Reference: Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s: section 2, Obesity hypoventilation syndrome (20 August 2021) — https://www.nice.org.uk/guidance/ng202/chapter/2-Obesity-hypoventilation-syndrome Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s: recommendations 2.5.8 and 2.7.6–2.7.8 (20 August 2021) — https://www.nice.org.uk/guidance/ng202/chapter/2-Obesity-hypoventilation-syndrome