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Protamine Reaction — FRCA Final MCQ

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HardCardiothoracic AnaesthesiaProtamine ReactionFRCA Final

A 52-year-old woman undergoes open aortic valve replacement. Within one minute of starting protamine after separation from cardiopulmonary bypass, her arterial pressure falls to 50/30 mmHg and pulmonary artery pressure rises from 28/14 to 65/40 mmHg. Transoesophageal echocardiography shows a newly dilated, severely hypokinetic right ventricle with septal flattening and a small, underfilled left ventricle. The surgical field is dry, and there is no bronchospasm, urticaria or facial oedema. What is the most likely diagnosis?

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Correct answer: B — Protamine-induced acute pulmonary vasoconstriction (type III reaction)

The diagnosis is **protamine-induced acute pulmonary vasoconstriction (type III reaction)**. The abrupt increase in pulmonary vascular resistance causes extreme right ventricular afterload, acute RV dilatation and failure, reduced flow through the lungs, LV underfilling and systemic hypotension. A type I reaction produces predominantly systemic hypotension, particularly with rapid administration, without marked pulmonary hypertension. Protamine anaphylaxis may cause profound hypotension but is more likely to include bronchospasm, cutaneous or mucosal features, and evidence of mast-cell activation. Heparin rebound causes recurrent anticoagulation and bleeding rather than an immediate rise in pulmonary artery pressure. Acute LV failure would show primary LV dysfunction and pulmonary venous congestion, not an underfilled LV with acute RV pressure overload. Protamine should be stopped, systemic pressure and RV function supported, and selective pulmonary vasodilation and return to bypass considered.

Reference: Wockhardt UK Ltd. Prosulf 10 mg/ml Solution for Injection, Summary of Product Characteristics, sections 4.4 and 4.8, updated 2018. https://www.medicines.org.uk/emc/product/8/smpc