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Life-threatening acute asthma — MRCEM SBA MCQ

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HardResuscitation and critical illnessLife-threatening acute asthmaMRCEM SBA

A 29-year-old woman with asthma presents with marked breathlessness. Her best peak expiratory flow (PEF) is 480 L/min. She receives oxygen titrated to an SpO₂ of 94–98%, oxygen-driven nebulised salbutamol and ipratropium, and oral prednisolone. Thirty minutes later she remains alert and able to speak in short phrases, but her PEF has fallen from 210 to 150 L/min. Her respiratory rate is 32/min, SpO₂ is 96% on oxygen, and an arterial blood gas shows pH 7.37 and PaCO₂ 5.3 kPa. There is no clinical evidence of pneumothorax. Which management plan is most appropriate now?

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Correct answer: C — Give intravenous magnesium sulphate, intensify nebulised salbutamol, and request immediate senior and critical care review.

Her PEF has fallen to approximately 31% of her personal best despite initial treatment: this is a life-threatening feature, not a reassuring response to bronchodilators. A PaCO₂ of 5.3 kPa is also concerning in an acute asthma attack; a ‘normal’ value can signal failing ventilation rather than recovery. An SpO₂ of 96% while receiving oxygen does not negate either finding. UK acute-asthma guidance supports more frequent or continuous nebulised salbutamol, consideration of a single intravenous magnesium sulphate infusion, and urgent senior and critical care involvement. Her deteriorating PEF also warrants close reassessment and preparation for escalation. ([nice.org.uk](https://www.nice.org.uk/guidance/qs25/documents/briefing-paper)) A provides bronchodilators and repeat testing but understates the urgency and misses escalation. B delays critical care review until hypercapnia develops; non-invasive ventilation is not the preferred next step in this alert patient. D uses aminophylline ahead of the recommended magnesium-and-senior-review sequence and proposes an insufficient level of care. E might become necessary if respiratory effort, consciousness or gas exchange deteriorates, but she is currently alert and maintaining ventilation, so immediate intubation is not the best next action. ([nice.org.uk](https://www.nice.org.uk/guidance/qs25/documents/briefing-paper))

Reference: Asthma (QS25) briefing paper, Appendix 6: Management of acute severe asthma in adults in hospital (2018) — https://www.nice.org.uk/guidance/qs25/documents/briefing-paper Asthma pathway (BTS, NICE, SIGN), NG244 (Last reviewed 27 November 2024) — https://www.nice.org.uk/guidance/ng244/resources/asthma-pathway-bts-nice-sign-pdf-66143956599493