Ionized magnesium supplementation in critically ill patients: comparing ionized and total magnesium.

PURPOSE

The purpose of this study was to assess the effect of magnesium supplementation on total magnesium, ionized magnesium, ionized calcium, potassium, and pH in critically ill cancer patients and to compare the validity of the measurements.

MATERIALS AND METHODS

Thirty-three consecutive critically ill patients receiving magnesium supplementation were placed in this prospective observational study at the Comprehensive Cancer Center, University Hospital. One gram (4.1 mmol) magnesium in 50 mL D5W was administered to critically ill patients, and the following were measured: total magnesium, ionized magnesium, ionized calcium, potassium, albumin, pH, BUN, creatinine, creatinine.

RESULTS

Total magnesium and ionized magnesium increased by a mean of .11 +/- .02 and .05 +/- .01 mmol/L, respectively, after supplementation with 4.1 mmol of magnesium sulfate (P = .0001). Total magnesium, ionized magnesium, albumin, ionized calcium, potassium, and pH did not change significantly by the administration of 1 g of magnesium sulfate.

CONCLUSION

The mean ionized magnesium (IMg+2) relationship to total magnesium (TMg) cannot be predicted before the supplementation with the available technology. After supplementation of 4.1 mmol/L the ionized magnesium level increased by .05 +/- .01 mmol/L. Magnesium supplementation had no significant effect on ionized calcium, potassium, and pH. TMg and IMg+2 should be followed independently.