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Obesity hypoventilation syndrome with acute-on-chronic hypercapnic respiratory failure — SCE Respiratory MCQ

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HardRespiratory FailureObesity hypoventilation syndrome with acute-on-chronic hypercapnic respiratory failureSCE Respiratory

A 56-year-old woman with a BMI of 58 kg/m² is admitted with increasing daytime somnolence and breathlessness. Her family describes several years of loud snoring, witnessed apnoeas and morning headaches, but she has never undergone sleep assessment. She has no smoking history or known obstructive lung disease. She is rousable, follows commands and can remove a face mask independently. Her respiratory rate is 22 breaths/min, SpO₂ is 89% while receiving controlled oxygen, and she is haemodynamically stable. There is an elevated jugular venous pressure and marked bilateral peripheral oedema. Chest radiography shows reduced lung volumes without focal consolidation. Echocardiography shows right ventricular dilatation with preserved left ventricular systolic function. Arterial blood gases show pH 7.36, PaCO₂ 9.0 kPa, PaO₂ 7.6 kPa and bicarbonate 39 mmol/L. She has received no sedative medication. Which immediate respiratory management plan is most appropriate?

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

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Correct answer: B — Start bilevel non-invasive ventilation with controlled oxygen targeting 88–92% and intravenous diuresis in a high-dependency or intensive care unit

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

The obesity, awake hypercapnia, markedly elevated bicarbonate and typical sleep-disordered breathing symptoms indicate obesity hypoventilation syndrome with chronic ventilatory failure. Her new somnolence, hypoxaemia and right-heart failure with fluid retention indicate acute decompensation despite the absence of respiratory acidosis. BTS/ICS guidance identifies an important exception to the usual pH-based NIV threshold: hospitalised obese hypercapnic patients with daytime somnolence, sleep-disordered breathing or right-heart failure may require NIV even when pH is at least 7.35. Oxygen should be controlled to 88–92%. Fluid overload commonly contributes to ventilatory failure in OHS and may be underestimated, making active diuresis appropriate. Because NIV failure is more frequent and intubation can be difficult, acute NIV should be delivered in an HDU/ICU environment. A delays ventilatory support for diagnostic testing, which should not precede treatment of acute ventilatory failure. B is attractive because CPAP is first-line for stable OHS with severe OSAHS, but bilevel NIV is preferred during acute ventilatory failure to improve ventilation and hypercapnia. C treats oxygenation without adequately supporting alveolar ventilation. D would be appropriate if she could not protect her airway, were unstable or failed NIV; none of these applies, so a closely monitored NIV trial is preferable.

Reference: BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults (March 2016; correction June 2017) — https://thorax.bmj.com/content/71/Suppl_2/ii1 BTS/ICS Guideline for the Ventilatory Management of Acute Hypercapnic Respiratory Failure in Adults (March 2016) — https://www.brit-thoracic.org.uk/clinical-resources/guidelines/niv/ Obstructive sleep apnoea/hypopnoea syndrome and obesity hypoventilation syndrome in over 16s: obesity hypoventilation syndrome (20 August 2021) — https://www.nice.org.uk/guidance/NG202/chapter/2-obesity-hypoventilation-syndrome