Ionised Calcium in MTP
Mar 05, 2026
The forgotten cofactor
Massive Transfusion Protocols are built around red cells, plasma and platelets. We talk about ratios, fibrinogen, tranexamic acid and warming. Yet one critical element is often quietly dropping in the background. Ionised calcium.
Calcium is essential for the coagulation cascade. It acts as a cofactor in multiple steps of clot formation and supports platelet function and myocardial contractility. During massive transfusion, citrate used as an anticoagulant in blood products binds ionised calcium. As transfusion volume increases, circulating ionised calcium levels can fall rapidly. Hypocalcaemia then contributes to hypotension, reduced cardiac output and worsening coagulopathy.
This is not just a laboratory number. It is physiology in motion.
🩸 Ionised calcium is required for effective clot formation
🩸 Citrate in blood products reduces circulating calcium levels
🩸 Hypocalcaemia impairs myocardial contractility and vascular tone
🩸 Low ionised calcium is associated with increased bleeding and mortality in major haemorrhage
For perianaesthesia nurses, this means anticipating the drop. In active MTP, request early and repeated ionised calcium measurements. Watch for hypotension that does not respond as expected to volume or vasopressors. Clarify local protocols for calcium replacement and ensure timely administration when indicated.
Calcium replacement is not an afterthought. It is part of haemostatic resuscitation. When we correct hypocalcaemia early, we support both the clotting cascade and cardiovascular stability.
Ionised calcium may be the forgotten cofactor in massive transfusion, but in the physiology of haemorrhage, it is central. Recognising this helps us deliver more complete, more protective care.
References
Khan, S., et al. (2022). Hypocalcaemia in trauma and massive transfusion: a review.
Zhang, Y., et al. (2021). The role of calcium in trauma-induced coagulopathy and massive transfusion. Annals of Blood.
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