[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 (Mg2+), we performed following studies. 1) We measured ionized Mg (Mg2+), total Mg, ionized Ca (Ca2+), total Ca and citrate before and after operation in 70 patients. 2) We evaluated the effect of citrate on Mg2+ and Ca2+ in vitro. 3) We also measured these values during blood transfusion in 8 patients. There was no significant difference between post-operative Mg2+ 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 +/- 0.09 mmol.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 Mg2+ about 2% in in vitro study. During blood transfusion, Mg2+ (0.41 +/- 0.05 mmol.l-1) and ionized % (54.5 +/- 8.3%) decreased significantly just like Ca2+ 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 Mg2+, and the major cause was thought to be the dilution of extracellular fluid by Mg-free fluid administered during operation.