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Salbutamol-associated lactic acidosis during treatment of acute asthma — MRCEM SBA MCQ

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HardRespiratory emergenciesSalbutamol-associated lactic acidosis during treatment of acute asthmaMRCEM SBA

A 28-year-old woman with asthma presents with marked breathlessness. Her initial peak expiratory flow (PEF) is 180 L/min; her documented personal best is 500 L/min. She receives oral prednisolone, nebulised ipratropium and repeated 5 mg nebulised salbutamol doses. Ninety minutes later, she is still breathing at 30/min, but can speak in full sentences, has good bilateral air entry with little wheeze, and her PEF is 410 L/min. Her SpO₂ is 97% on air, blood pressure is 124/78 mmHg and temperature is 36.8°C. Arterial blood gas analysis shows pH 7.43, PaCO₂ 3.2 kPa, bicarbonate 16 mmol/L and lactate 6.1 mmol/L; lactate was 1.6 mmol/L on arrival. She is alert and well perfused, and chest radiography shows no consolidation. Salbutamol is still being given every 20 minutes. What is the most appropriate next management plan?

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Correct answer: A — Space salbutamol to as-needed doses and observe with repeat PEF and lactate.

Her initial PEF was 36% of personal best, warranting treatment for acute severe asthma. It has risen to 82%, with improved speech and air entry and satisfactory oxygenation. The persistent tachypnoea therefore does not, by itself, establish ongoing severe bronchospasm. The new lactate rise and low bicarbonate after repeated salbutamol are consistent with beta₂-agonist-associated lactic acidosis; compensatory hyperventilation can be mistaken for treatment failure. Space salbutamol rather than intensifying it, while observing her and repeating PEF, lactate and clinical assessment. Other causes of lactataemia must remain under review. ([medicines.org.uk](https://www.medicines.org.uk/emc/product/10257/smpc?utm_source=openai)) **B** risks perpetuating the suspected drug effect despite objective improvement in airflow. **C** is a reasonable escalation when severe asthma responds poorly to initial bronchodilators, not when PEF and examination have substantially improved. **D** does not address the apparent cause of tachypnoea: she is alert, oxygenating adequately and hypocapnic rather than developing hypercapnic ventilatory failure. **E** is premature. Although PEF exceeds a usual discharge threshold, she remains tachypnoeic with substantial new lactataemia and needs reassessment before disposition. ([doclibrary-rcht.cornwall.nhs.uk](https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/Respiratory/AcuteExacerbationsOfAsthmaInAdultsClinicalGuideline.pdf))

Reference: Salbutamol 2 mg/mL nebuliser solution — Summary of Product Characteristics, section 4.4 (18 November 2025) — https://www.medicines.org.uk/emc/product/10257/smpc Acute Exacerbation of Asthma in Adults Clinical Guideline V4.0 (June 2026) — https://doclibrary-rcht.cornwall.nhs.uk/DocumentsLibrary/RoyalCornwallHospitalsTrust/Clinical/Respiratory/AcuteExacerbationsOfAsthmaInAdultsClinicalGuideline.pdf Conundrum in an asthma exacerbation (2016) — https://casereports.bmj.com/content/2016/bcr-2016-214360.full?sid=19fe9691-0e99-43df-bcd0-e3a5b5c0ade7