What is the most likely complication in a patient receiving a massive blood transfusion (greater than 10 units of blood or 1 blood volume in 24 hours)?

Hypocalcemia is the Most Likely Complication

The most likely complication following massive blood transfusion of 4 litres in this trauma patient is hypocalcemia (Option C), caused by citrate toxicity from the anticoagulant in stored blood products.

Mechanism of Hypocalcemia in Massive Transfusion

Citrate in blood products binds ionized calcium, leading to hypocalcemia during rapid transfusion. 1 Blood products contain citrate as an anticoagulant, which exerts its effect by chelating ionized calcium. 1 During massive transfusion, the rapid administration of citrate-containing products (particularly fresh frozen plasma and platelets, which have the highest citrate concentrations) overwhelms the liver's ability to metabolize citrate, resulting in hypocalcemia. 1

• Citrate metabolism is dramatically impaired by hypoperfusion states, hypothermia, and hepatic insufficiency—all common in trauma patients. 1
• The normal ionized calcium concentration ranges from 1.1 to 1.3 mmol/L, and levels should be maintained >0.9 mmol/L during massive transfusion. 1

Clinical Significance and Prevalence

Hypocalcemia occurs in 85-97% of patients undergoing massive transfusion protocols. 2 Recent studies demonstrate that:

• 97% of patients develop hypocalcemia during the first six hours of massive transfusion resuscitation. 2
• 59.1% of patients experience severe hypocalcemia (ionized calcium ≤1.0 mmol/L). 3
• Patients receiving 13 or more units of packed red blood cells have an 83.3% prevalence of severe hypocalcemia. 3
• The nadir typically occurs after a median of 8 units of blood products. 2

Impact on Morbidity and Mortality

Low ionized calcium levels at admission are associated with increased mortality and increased need for massive transfusion. 1 The clinical consequences include:

• Impaired fibrin polymerization and decreased platelet function, contributing to coagulopathy. 1
• Decreased cardiac contractility and reduced systemic vascular resistance. 1
• Hypocalcemia during the first 24 hours predicts mortality better than fibrinogen levels, acidosis, or platelet counts. 1

Guideline Recommendations

European trauma guidelines recommend monitoring and maintaining ionized calcium levels within the normal range during massive transfusion (Grade 1C recommendation). 1 Specifically:

• Ionised calcium levels should be monitored regularly during massive transfusion. 1
• Calcium levels should be maintained within the normal range throughout resuscitation. 1
• Both hypocalcaemia and hypomagnesaemia are commonly associated with massive transfusion and require monitoring and correction. 1

Why Other Options Are Less Likely

Hypokalaemia (Option A) is incorrect because massive transfusion typically causes hyperkalemia initially (from potassium release from stored red blood cells), though hypokalemia may develop later during the recovery phase. 4, 5

Citrate toxicity (Option B) is the mechanism causing hypocalcemia, not a separate complication—it manifests clinically as hypocalcemia. 4, 5

Hyperalbuminemia (Option D) is incorrect because massive transfusion causes hemodilution, not concentration of albumin.

Clinical Pitfall

A common error is prophylactic calcium administration without monitoring, which is dangerous and unnecessary. 4 Calcium supplementation should be guided by ionized calcium measurements, not given empirically. 1 However, the widespread variability in calcium monitoring and supplementation during massive transfusion represents a significant gap in current practice. 3, 2