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Iodinated contrast media-induced anaphylaxis — SCE Respiratory MCQ

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HardContrast AllergyIodinated contrast media-induced anaphylaxisSCE Respiratory

A 63-year-old man with severe asthma undergoes iodinated contrast-enhanced CT angiography to define the source of recurrent haemoptysis. Within 2 minutes of receiving iohexol, he develops widespread wheeze, oxygen desaturation and profound hypotension. There is no urticaria or angioedema. Contrast administration is stopped. He receives high-flow oxygen, two intramuscular doses of adrenaline 500 micrograms at 5-minute intervals and 2 L of intravenous crystalloid. Because cardiovascular and respiratory compromise persists, critical care starts a monitored low-dose intravenous adrenaline infusion. Despite titration of the infusion and further fluid resuscitation, his blood pressure remains 68/40 mmHg, heart rate 54 beats/min and oxygen saturation 89%, with continuing wheeze. His regular medication includes propranolol 80 mg twice daily for essential tremor. Which additional drug most directly addresses the likely reason for his refractory cardiovascular response?

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Correct answer: A — Intravenous glucagon

This is immediate, severe contrast-media hypersensitivity causing anaphylactic shock and bronchospasm. The absence of cutaneous manifestations does not outweigh the close temporal relationship and combined respiratory and cardiovascular compromise. Appropriate first-line treatment has already been delivered: contrast cessation, oxygen, intramuscular adrenaline and rapid crystalloid resuscitation, followed by a specialist intravenous adrenaline infusion for refractory anaphylaxis. Propranolol explains the unusually poor cardiovascular response and relative bradycardia: beta-adrenoceptor blockade may reduce the effectiveness of adrenaline. Glucagon activates adenylate cyclase independently of beta-adrenoceptors and is therefore the most targeted additional treatment when anaphylaxis remains refractory to an adrenaline infusion and adequate fluids in a beta-blocked patient. Salbutamol is a useful adjunct for persistent bronchospasm but does not adequately treat anaphylactic shock and may itself be less effective during beta-blockade. Hydrocortisone has a delayed onset and must not displace haemodynamic resuscitation. Vasopressin can be considered as an additional vasopressor in refractory vasoplegia, but the explicit beta-blocker-associated catecholamine resistance makes glucagon the better targeted answer. Atropine may increase the heart rate but does not correct the underlying anaphylactic vasodilatation, capillary leak or bronchospasm.

Reference: Hypersensitivity reactions to contrast media: Part 1. Management of immediate and non-immediate hypersensitivity reactions in adults. Updated guidelines by the ESUR Contrast Media Safety Committee (27 May 2025) — https://pubmed.ncbi.nlm.nih.gov/40425758/ Resuscitation Council UK: Refractory anaphylaxis (2021) — https://www.sort.nhs.uk/Media/Guidelines/Anaphylaxis-Refractory.pdf