Cancer-associated thrombosis — SCE Respiratory MCQ

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HardPulmonary Vascular DiseaseCancer-associated thrombosisSCE Respiratory

A patient receiving topical benzocaine becomes cyanosed. SpO2 remains 85% despite oxygen, arterial PaO2 is 40 kPa and the blood is chocolate-brown. What is the diagnosis?

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Correct answer: E — Methaemoglobinaemia

The saturation gap—low pulse oximetry despite a very high PaO2—plus chocolate-brown blood after an oxidant exposure is characteristic of methaemoglobinaemia. Co-oximetry confirms the diagnosis. Symptomatic clinically important disease is treated with methylene blue unless contraindicated, particularly in G6PD deficiency.

Reference: BTS Guideline for Oxygen Use in Adults. https://www.brit-thoracic.org.uk/quality-improvement/guidelines/emergency-oxygen/