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Acute-on-chronic hypercapnic respiratory failure in neuromuscular disease — SCE Respiratory MCQ

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HardHypercapnic Respiratory FailureAcute-on-chronic hypercapnic respiratory failure in neuromuscular diseaseSCE Respiratory

A 46-year-old man with limb-girdle muscular dystrophy is admitted with fever, purulent sputum and increasing orthopnoea. He does not use domiciliary ventilatory support. He is alert, can remove a face mask independently and has no bulbar weakness or haemodynamic instability. Controlled oxygen at 24% maintains SpO₂ at 90%. His respiratory rate is 27 breaths/min. Supine vital capacity is 0.68 L, compared with 1.05 L three months earlier. Arterial blood gases show pH 7.37, PaCO₂ 7.8 kPa, PaO₂ 8.0 kPa and bicarbonate 34 mmol/L. Chest radiography shows left basal atelectasis without pneumothorax. Despite manual assisted coughing and physiotherapy, he has audible retained secretions and a peak cough flow of 130 L/min. He has previously requested invasive ventilation if potentially reversible respiratory failure cannot be managed non-invasively. Which respiratory management plan is most appropriate now?

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

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Correct answer: B — Start pressure-targeted NIV with a mandatory backup rate and mechanical insufflation–exsufflation in HDU or ICU

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

This is acute-on-chronic ventilatory pump failure complicating neuromuscular disease. The near-normal pH reflects renal compensation and must not delay support: he is acutely unwell, hypercapnic, tachypnoeic and has a vital capacity well below 1 L. NIV should therefore be instituted before respiratory acidosis develops. Profound respiratory muscle weakness may cause ineffective patient triggering, favouring pressure-targeted NIV with a mandatory backup rate rather than a purely spontaneous mode. His very low peak cough flow, retained sputum and atelectasis additionally require mechanical insufflation–exsufflation. HDU or ICU is appropriate because deterioration in neuromuscular respiratory failure may be abrupt and invasive ventilation remains within his agreed escalation plan. A is inappropriate because normal pH does not justify observation when hypercapnia and severe neuromuscular weakness are already present. B provides ventilatory support but may fail through ineffective triggering and does not adequately address secretion retention. D would become appropriate if NIV failed, airway protection deteriorated or immediate life-threatening instability developed; none is currently present, so a monitored NIV trial should precede intubation. E may improve oxygenation and cough-assist access but does not reliably correct alveolar hypoventilation from respiratory muscle failure. Oxygen should remain controlled because excessive oxygenation can worsen hypercapnia without treating the underlying pump failure.

Reference: BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults (March 2016; correction June 2017) — https://www.brit-thoracic.org.uk/document-library/guidelines/niv/btsics-guideline-for-the-ventilatory-management-of-acute-hypercapnic-respiratory-failure-in-adults/ Motor neurone disease: assessment and management (NG42) — Recommendations (Published 24 February 2016; updated 23 July 2019) — https://www.nice.org.uk/guidance/NG42/chapter/Recommendations