A 40-year-old woman with postpartum hemorrhage receives massive transfusion comprising 15 units packed red blood cells, 10 units fresh frozen plasma, and 2 pools of platelets over 3 hours. She develops peroral numbness, carpopedal spasm, and ECG shows prolonged QT interval. Which mechanism best explains this complication?

• A Hyperkalemia from stored red blood cells
• B Citrate toxicity binding ionized calcium ✓
• C Hypothermia from rapid transfusion
• D Dilutional thrombocytopenia

Explanation

Citrate is the anticoagulant in stored blood products. Each unit of packed red cells contains approximately 3 grams of citrate. Massive transfusion overwhelms the liver's capacity to metabolize citrate, leading to ionized hypocalcemia. This manifests as neuromuscular irritability, prolonged QT interval, and cardiac dysfunction. Hyperkalemia causes peaked T waves and widened QRS. Hypothermia causes arrhythmias but not prolonged QT with spasms. Thrombocytopenia causes bleeding.

Reference: Bailey and Love's Short Practice of Surgery, 28th ed.

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Written and medically reviewed by the StethoPrep medical team.