Magnesium at admission: is it an outcome marker in the critically ill patient?

Introduction

Magnesium (Mg) is the fifth most common cation in the body, considered, however, as the 'forgotten cation' in clinical practice [1]. Mg deficiency is rather common in critically ill patients and recent studies found that reductions in total serum Mg at admission are associated with increased mortality [2]. Loss of Mg can lead to vasoconstriction, especially of cerebral and coronary arteries, while Mg appears to play a role in the scavenging of free radicals and the prevention of reperfusion injury [3].

Aim

An observational study on the evaluation of total serum Mg in a tertiary 10-bed intensive care unit.

Patients

Ninety-five patients admitted to the ICU over a 6-month period: 30 polytrauma, 11 COPD, 12 stroke, nine liver transplantation, 13 postoperative, five eclampsia and 15 miscellaneous. Mean age: 43.2 years, length of stay: 9.2 days, APACHE II score: 11.3 ± 7.5, mortality: 34%.

Measurements and results

Total serum Mg, calcium, phosphorus and proteins were measured at admission and then every day until discharge from the ICU. At admission, 15/30 polytrauma, 6/13 postoperative, 4/12 stroke, 5/5 eclampsia, 8/9 liver transplantation, 2/11 COPD and 5/15 miscellaneous patients had <1.3 mg/dl total serum Mg. Calcium and phosphorus deficiency was not remarkable in any of the groups, while total proteins were found in relatively low levels (< 3.5 mg/dl) in polytrauma and postoperative patients. Low APACHE II score and negative outcome had a relative correlation with low Mg levels in all groups, whereas Mg replacement had not affected patients' outcome. ICU length of stay had no correlation to low Mg levels at admission.

Conclusion

Hypomagnesemia at admission is relatively associated with a worse prognosis, considering, however, that other major factors (e.g. sepsis, MODS) play the first role in critically ill patients' outcome.