Perioperative change of ionized magnesium concentration - Effect of blood transfusion

In order to evaluate the effect of intra-operative blood transfusion on post-operative decrease of ionized Mg (Mg ²⁺), we performed following studies. 1) We measured ionized Mg (Mg ²⁺), total Mg, ionized Ca (Ca ²⁺), total Ca and citrate before and after operation in 70 patients. 2) We evaluated the effect of citrate on Mg ²⁺ and Ca ²⁺ in vitro. 3) We also measured these values during blood transfusion in 8 patients. There was no significant difference between post-operative Mg ²⁺ of 45 patients without blood transfusion (0.49±0.07 mmol · l ^-1, % decrease from pre-operative value was 13.4± 9.2%; mean±SD), and that of 25 patients with blood transfusion (0.48±0.09mmol · l ^-1, 17.9±10.2%). Mean value of post-operative citrate concentration of patients with blood transfusion was 0.15±0.11 mmol · l ^-1, and this value decreased Mg ²⁺ about 2% in in vitro study. During blood transfusion, Mg ²⁺ (0.41±0.05 mmol · l ^-1) and ionized % (54.5±8.3%) decreased significantly just like Ca ²⁺ with elevated citrate concentration (0.95±0.59 mmol · l ^-1). In conclusion, intra-operative blood transfusion had minor effect on the post-operative decrease of Mg ²⁺, and the major cause was thought to be the dilution of extracellular fluid by Mg-free fluid administered during operation.