Q: Massive blood transfusion may cause clinically symptomatic hypocalcemia due to added citrate in pRBC. What is the 'rule of thumb' for calcium replacement during massive blood transfusion?



Answer: 1:3 

One calcium gluconate ampule per three pRBC bags

To be precise, 10 mL of  calcium gluconate be given per 250 mL of blood OR  5 mL of calcium chloride should be given per 250 mL of blood.  Some authorities prefer calcium chloride over calcium gluconate.

The risk of citrate toxicity (causing hypocalcemia)  increases with liver insufficiency or in "shock liver", which is very common in such circumstances. 



Reference: 

British Committee for Standards in Haematology, Stainsby D, MacLennan S, et al. Guidelines on the management of massive blood loss. Br J Haematol 2006; 135:634.