Methaemoglobinaemia at bronchoscopy in G6PD deficiency26-year-old man, 70 kg, for diagnostic flexible bronchoscopy under topical anaesthesia and light sedation

The patient

The examiner asks

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1. Consider

   What are your concerns?

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   • A 26-year-old with G6PD deficiency, for flexible bronchoscopy under topical anaesthesia and light sedation. Patient
   • His red cells can't cope with oxidative stress; oxidant drugs can trigger acute haemolysis. Disease
   • Topical local anaesthetics, especially benzocaine and prilocaine, can cause methaemoglobinaemia. Stem trigger
   • If that happens, methylene blue may not work for him and can haemolyse him. Disease
   • Infection, acidosis, high glucose and cold can also set off his haemolysis. Stem trigger

2. Plan

   How will you manage his sedation and topical anaesthesia?

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   • Lidocaine is also an oxidant risk: the least that works, well under 9 mg/kg, co-oximetry ready. Stem trigger
   • No benzocaine or prilocaine; I track the total lidocaine sprayed, since it adds up fast. Airway
   • Midazolam 1–2 mg for sedation is safe in G6PD deficiency; no diazepam. Disease
   • Every other drug, including antibiotics, checked against the G6PD unsafe list. Stem trigger
   • Capnography and oxygen throughout the sedation. Disease

3. Crisis

   Twenty minutes in, SpO2 drifts from 98% to 86% despite 6 L/min of oxygen; his lips look grey-blue and his blood looks dark. What do you do?

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   • Methaemoglobinaemia until proven otherwise: falling SpO2 despite oxygen after topical anaesthetic. (Crisis)
   • Stop the local anaesthetic and the procedure; high-flow oxygen.
   • His oximeter heads to 85% whatever his true saturation, so I don't trust it.
   • Arterial gas with co-oximetry: his saturations will disagree, and it measures methaemoglobin.
   • No more sedation; airway and breathing supported while the result comes.

4. Crisis

   Co-oximetry shows methaemoglobin 38%. He is confused; HR 128, BP 96/60. What now?

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   • Life-threatening methaemoglobinaemia; methylene blue would be first-line, but not for him. Crisis
   • In G6PD deficiency it may not work and may cause haemolysis.
   • Exchange transfusion is his main option for severe disease.
   • Ascorbic acid as an alternative, though it acts slowly over hours.
   • Hyperbaric oxygen if available, accepting the fall may take hours.
   • Hb and haemolysis screen repeated over the next days. After surgery
   • ICU; the reaction recorded and his oxidant drug list given to him.