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Acute exacerbation of COPD: oxygen titration after initial blood gases — MRCEM SBA MCQ

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EasyRespiratory emergenciesAcute exacerbation of COPD: oxygen titration after initial blood gasesMRCEM SBA

A 68-year-old man with established COPD attends the emergency department with increased breathlessness and sputum production. His usual resting SpO₂ is 96% on air, and he has no history of hypercapnic respiratory failure or non-invasive ventilation. Oxygen was started through a 28% Venturi mask while blood gases were obtained. He is alert and haemodynamically stable; SpO₂ is now 90%. Arterial blood gas analysis on 28% oxygen shows pH 7.40, PaCO₂ 4.8 kPa, bicarbonate 23 mmol/L and PaO₂ 8.1 kPa. Bronchodilators and systemic corticosteroids have been started. What is the most appropriate oxygen and blood-gas monitoring plan now?

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

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Correct answer: E — Titrate oxygen to SpO₂ 94–98% and repeat arterial blood gases in 30–60 minutes.

The initial 88–92% target is appropriate while blood gases are pending in a patient with COPD. Here, however, both pH and PaCO₂ are normal. He has neither previous hypercapnic respiratory failure requiring ventilatory support nor a usual stable SpO₂ below 94%. The British Thoracic Society oxygen guideline therefore supports changing the target to 94–98%. COPD remains a risk factor for developing hypercapnia after oxygen is increased, so arterial blood gases should be repeated in 30–60 minutes to check for a rising PaCO₂ or falling pH. ([thorax.bmj.com](https://thorax.bmj.com/content/72/Suppl_1/ii1?utm_source=openai)) **A** retains the precautionary oxygen target despite the reassuring blood gas and history. It would be appropriate if he had previously required ventilatory support for hypercapnic failure. **B** selects the appropriate target but omits the early repeat gas; that approach better fits a patient without risk of hypercapnic respiratory failure. **C** retains the inappropriate target and delays reassessment. **D** corrects the target but waits too long for the first repeat gas after increasing oxygen. NICE also recommends documenting inspired oxygen concentration with blood gases and repeating measurements according to the response to treatment. ([nice.org.uk](https://www.nice.org.uk/guidance/ng115/chapter/Recommendations))

Reference: BTS guideline for oxygen use in adults in healthcare and emergency settings (2017) — https://thorax.bmj.com/content/72/Suppl_1/ii1 NICE NG115: Chronic obstructive pulmonary disease in over 16s: diagnosis and management (26 July 2019) — https://www.nice.org.uk/guidance/ng115/chapter/Recommendations