Ionized Magnesium in Critically Ill Patients as Measured by an Ion Selective Electrode

Abstract

Despite its physiological importance, physiologically active ionized magnesium (iMg²⁺) has not been measured in critically ill patients for lack of methodology. A new magnesium ion selective electrode was used to measure whole blood iMg²⁺ and ionized calcium (iCa²⁺) in 29 critically ill patients and 36 healthy volunteers.
Levels of iMg²⁺ were significantly lower on admission (0.47±0.08mmol·1^-1, mean±SD) and at 6±1 ICU days (0.48±0.12mmol·1^-1) in the patient group than in the control group (0.53±0.04mmol·1^-1). There was no correlation between iMg²⁺ and total magnesium in the critically ill patients. Levels of ionized Ca²⁺ showed the same trends as iMg²⁺, however, the ratio of iMg²⁺/iCa²⁺ at the two points in the patient group were not different from that of the control group. The significant correlation between iMg²⁺ and iCa²⁺ found in the control group was not seen on admission in the patient group, but was re-established at 6±1 ICU days.
Ionized magnesium (iMg²⁺) decreases in critically ill patients making it an important measure to monitor.