During massive transfusion following a ruptured abdominal aortic aneurysm repair, a patient develops perioral tingling, carpopedal spasm and a prolonged QT interval. Which investigation and intervention are MOST appropriate?

• A Ionised calcium; give IV calcium guided by the level ✓
• B Serum total calcium; give 10% calcium gluconate empirically
• C Serum magnesium; give magnesium sulphate 2 g IV
• D Serum potassium; give insulin-dextrose infusion

Explanation

Citrate anticoagulant in stored blood chelates ionised calcium. Rapid transfusion exceeds the liver's capacity to metabolise citrate, producing hypocalcaemia with neuromuscular irritability and QT prolongation. Total serum calcium is unreliable because half is protein-bound and levels shift with haemodilution and alkalosis, so ionised calcium is the correct measurement during massive transfusion. Treatment is IV calcium chloride or gluconate titrated to the measured ionised level rather than given blind.

Reference: Miller's Anesthesia, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.