Thursday July 13, 2006
Case: 54 year old male with history of alcoholic cirrhosis, brought to ED after fall and found to have intracranial bleed. INR noted to be 1.5. Neurology service wrote for FFP (fresh frozen plasma) and IV Vitamin K. Patient admitted to ICU after neurosurgery decided to go conservative route. At admission patient mental status seems appropriate but 2 hours after admission you have been called as patient noted to have seizures by bedside staff. On arrival you noticed patient having generalized muscular contractions but he respond appropriately to your questions.
Probable etiology is: Hypocalcemia induced by citrate present in FFP.
Citrate is usually used in blood products as anticoagulant. It binds to free calcium to form soluble calcium citrate, thereby lowering the free (ionized) but not the total serum calcium concentration. It is important to check the ionized calcium instead of total serum calcium. The slower infusion rate has shown significantly less reduction in ionized calcium than did the higher infusion rates.
Prophylactic calcium infusion is not recommended with each blood product transfusion unless clinically indicated. Citrate is normally rapidly excreted by the liver and transient hypocalcemia is not necessary to treat. However, when a patient receives more than 1 unit of erythrocytes/blood product every 5 minutes or the capacity of the liver to metabolize citrate effectively is exceeded (like in our patient above with cirrhosis), the associated hypocalcemia can cause depressed ventricular contractility and decreased peripheral vascular resistance, causing arrhythmias, hypotension and neurologic symptoms of tetany.
Remember: In addition to calcium, citrate binds to magnesium, which can result in clinically important hypomagnesemia too.