Preoperative Ionized Magnesium Assessment

The reported incidence of hypomagnesemia is approximately 2% in the general population. Hypomagnesemia is a common problem, occurring in nearly 10%of general hospitalized patients and 17% of hospitalized cancer patients. A higher incidence, up to 60% to 65%, has been found among intensive care unit patients. Hypomagnesemia can potentially cause fatal complications including ventricular arrhythmia, coronary artery spasm, and sudden death. It also associates with increased mortality and prolonged hospitalization.

Magnesium exists in three different forms in the body. In serum, 5-14% of the magnesium is reported to be complexed with anions such as phosphate, bicarbonate, and citrate, 19-33% is reported to be protein-bound (mainly to albumin), and 55-67% is found in the free ionized fraction. Because the amount of bound or complexed Mg can vary significantly, especially in illness, the ionized magnesium can vary in an unpredictable way. Conventional laboratory testing typically only measures total serum magnesium, which is often not reflective of ionized magnesium. Unlike ionized calcium, which is commonly measured and is also readily calculated from the total calcium and albumin levels, ionized magnesium is neither commonly measured nor easily calculated. One study reported that the level of ionized magnesium cannot be predicted by analysis of total magnesium and that the levels of ionized magnesium vary upon different pathophysiological conditions and between individuals. Furthermore, measurement of ionized magnesium in serum might be of great impact in patients for whom magnesium status is required, and the correlation of ionized magnesium and total magnesium is weak in patients for whom magnesium status is required as a whole, and this is the reason why the ionized magnesium should be measured directly.

To date, most of the clinical studies were evaluate the effect of hypomagnesemia on the outcome after surgery using the levels of total serum magnesium. However, the portion of extracellular magnesium that is physiologically active is in the various process is ionized magnesium. So, it is important to evaluate the level of ionized magnesium in surgical patients to predict the outcomes after surgery. Unfortunately, clinical trial regarding the effect of the concentrations of ionized magnesium on the surgical patients is limited.