[Influence of fluid replacement on serum magnesium concentration and proper magnesium supplementation during general anesthesia].

We have studied the influence of fluid replacement on serum magnesium (Mg2+) concentrations, and studied proper Mg2+ supplementation during general anesthesia. Thirty eight patients undergoing elective surgery randomly received: Mg(2+)-free acetated Ringer solution (Group I, n = 15), acetated Ringer solution containing 0.5 mmol.l-1 of Mg2+ (Group II, n = 6), 1.0 mmol.l-1 of Mg2+ (Group III, n = 7), 2.0 mmol.l-1 of Mg2+ (Group IV, n = 6), or 4.0 mmol.l-1 of Mg2+ (Group V, n = 4). Measurements were made on serum and urine Mg2+ concentrations during anesthesia. In Group I, the serum Mg2+ concentrations decreased in correspondence with the water balance. It is suggested that dilution due to the fluid replacement induced the reduction in serum Mg2+ concentrations since the observed urine Mg2+ concentrations were negligible. In Group II-V, the reduction in serum Mg2+ concentrations was inhibited by Mg2+ supplementation, and the serum Mg2+ concentrations remained unchanged in Group IV. We conclude the Mg2+ supplementation is required during anesthesia when a large amount of fluid is infused.