A trauma patient receives massive transfusion (10 units pRBC in 6 hours). His ionized calcium is now 0.9 mmol/L (low). He develops hypotension with a widened QRS. The cause of hypocalcaemia in this context is:

• A Haemodilution from crystalloid co-administration
• B Hypomagnesaemia from transfusion
• C Transfusion-associated acute lung injury (TRALI)
• D Citrate toxicity chelating ionized calcium ✓

Explanation

Stored blood contains citrate as an anticoagulant preservative. During massive transfusion, citrate accumulates and chelates ionized calcium, causing hypocalcaemia. In normal circumstances, the liver metabolizes citrate rapidly, but in massive transfusion (or hepatic dysfunction), citrate accumulation causes haemodynamically significant ionized hypocalcaemia. Intravenous calcium gluconate (10 mL 10%) is given during massive transfusion to correct this. Calcium should be monitored every 4 units of blood transfused.

Reference: Bailey & Love's Short Practice of Surgery, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.