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Life-threatening acute asthma — MRCEM SBA MCQ

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HardRespiratory emergenciesLife-threatening acute asthmaMRCEM SBA

A 29-year-old woman with asthma attends the emergency department with worsening wheeze. Her usual best peak expiratory flow (PEF) is 540 L/min. On arrival it is 205 L/min. She receives oxygen-driven nebulised salbutamol and ipratropium and oral prednisolone 40 mg. Thirty minutes later she remains breathless, and her PEF is 145 L/min. Her respiratory rate is 29/min and SpO₂ is 95% on oxygen. An arterial blood gas shows pH 7.38 and PaCO₂ 5.1 kPa. She is alert and maintaining respiratory effort. Which is the most appropriate next management plan?

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

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Correct answer: B — Continue frequent nebulised salbutamol, give intravenous magnesium sulphate and seek urgent critical-care assessment.

Her PEF has fallen from approximately 38% to 27% of her usual best despite initial treatment. A PEF below 33% is a life-threatening feature. PaCO₂ of 5.1 kPa is not reassuring: a value in the normal range during a severe asthma attack is itself a life-threatening blood-gas marker. The falling PEF warrants urgent critical-care assessment while oxygen-driven nebulised bronchodilation continues. Following senior consultation, intravenous magnesium sulphate is the appropriate adjunct; the Royal Cornwall guideline specifies 2 g over 20 minutes. ([doclibrary-rcht.cornwall.nhs.uk](https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/Respiratory/AcuteExacerbationsOfAsthmaInAdultsClinicalGuideline.pdf)) A retains an essential treatment but misses the required escalation and assessment before deciding on ward placement. C is plausible because a senior clinician may consider aminophylline in refractory asthma, but magnesium has not yet been given. D is plausible in an exceptionally difficult attack, particularly when inhaled treatment cannot be delivered reliably; inhaled delivery is feasible here, so intravenous salbutamol is not the preferred next adjunct. E addresses possible respiratory support but does not replace the indicated pharmacological escalation. She has neither hypercapnic acidosis nor failing respiratory effort requiring an immediate ventilation decision. ([transformationpartners.nhs.uk](https://www.transformationpartners.nhs.uk/wp-content/uploads/2017/10/British-guideline-on-the-management-of-asthma.pdf))

Reference: Acute Exacerbation of Asthma in Adults Clinical Guideline, version 4.0 (June 2026) — https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/Respiratory/AcuteExacerbationsOfAsthmaInAdultsClinicalGuideline.pdf British guideline on the management of asthma: quick reference guide (October 2014) — https://www.transformationpartners.nhs.uk/wp-content/uploads/2017/10/British-guideline-on-the-management-of-asthma.pdf Asthma pathway (BTS, NICE, SIGN), NG244 (27 November 2024) — https://www.nice.org.uk/guidance/ng244?UID=46637734320251613825