Six hours after receiving 3 units of packed red cells, a ventilated post-operative patient develops abrupt hypoxaemia with bilateral infiltrates on chest radiograph. PaO2/FiO2 is 150. CVP is 8 mmHg and BNP is undetectable. Which mechanism explains this transfusion reaction?

• A Volume overload from passive transfer of donor plasma sodium
• B Donor anti-HLA or anti-granulocyte antibodies causing capillary leak in the recipient lung ✓
• C Recipient IgE-mediated mast cell degranulation against donor plasma proteins
• D Citrate-induced myocardial depression reducing pulmonary perfusion

Explanation

TRALI is defined as new acute lung injury within 6 hours of transfusion without circulatory overload. It is driven mainly by donor anti-HLA or anti-neutrophil antibodies that activate recipient neutrophils sequestered in pulmonary capillaries, producing non-cardiogenic oedema. The undetectable BNP and low CVP exclude TACO, the most tempting distractor, which presents with high filling pressures and elevated BNP. Allergic reactions cause urticaria or bronchospasm rather than bilateral alveolar infiltrates.

Reference: Sabiston Textbook of Surgery, 21st ed.

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