A trauma patient receives 18 units of packed red cells over 6 hours on a massive transfusion protocol. He develops perioral tingling, carpopedal spasm, and a prolonged QT interval on ECG. Ionised calcium is 0.75 mmol/L. What is the underlying cause and its treatment?

• A Potassium load from stored blood; insulin and dextrose infusion
• B Citrate chelation of calcium; intravenous calcium gluconate or calcium chloride ✓
• C Dilutional thrombocytopenia; platelet concentrate transfusion
• D Hypermagnesaemia from anticoagulant preservative; magnesium-free crystalloid

Explanation

Stored blood contains citrate as anticoagulant, which chelates ionised calcium. Rapid large-volume transfusion overwhelms hepatic citrate metabolism, causing hypocalcaemia with neuromuscular irritability and QT prolongation. Treatment is intravenous calcium chloride via central line or calcium gluconate peripherally. Hyperkalaemia is the tempting distractor but produces peaked T waves and widened QRS rather than tetany and QT prolongation, and it becomes significant mainly with very old units or pre-existing renal impairment.

Reference: Schwartz's Principles of Surgery, 11th ed.

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Written and medically reviewed by the StethoPrep medical team.