Monitoring magnesium to guide magnesium therapy for heart surgery

Abstract

ionized Mg (iMg). Measurement of TMg requires the isolation of plasma (centrifugation of blood sample) or serum (clotting and centrifugation of blood sample). Measurement is made by atomic absorption spectrophotometry or colorimetry. Reference values for plasma and serum TMg typically range from 0.66 to 1.07 mmol·l Ϫ1 . There is virtually no correlation between plasma/serum TMg and intracellular TMg.Ionized magnesium (iMg ϭ Mg 2ϩ ) represents the activity of unbound Mg in whole blood plasma, plasma, and/or serum. It is the physiologically active Mg fraction, i.e., the fraction to which tissues respond. Reference values typically range from 0.45 to 0.62 mmol·l Ϫ1 . The fact that it can be measured in a whole blood sample by electrode produces a rapid result (Ͻ150 s) on a small sample (Ͻ200 µl). A rapid result can be very helpful for patients (1) with arrhythmia, (2) with changes in cardiac output, (3) receiving cardiovascular drugs, (4) sustaining hypoxic damage, and (5) receiving Mg therapy. Blood plasma iMg correlates with intracellular iMg and therefore represents a better indicator of Mg status than TMg. It is typically 70% of the TMg value, but varies with the protein and small ligand concentrations in the blood. The iMg value may be substantially less than 70% of the TMg value in critically ill patients where binding ligand concentrations (heparin, citrate, lactate, phosphate, bicarbonate, etc.) have increased.Comparisons of iMg to TMg were illustrated in nine clinical settings (hypertension, acute myocardial infarction, head trauma, noninsulin-dependent diabetes, stroke, pregnancy, ischemic heart disease, cyclosporin recipients, and asthma) [3]. Ionized magnesium was found to be a better indicator of disease than TMg. In summary, iMg (1) represents the physiologically important Mg measurement, (2) is a better indicator of disease than TMg, and (3) is a more rapid measurement.The literature should be interpreted with caution. Frequently, if not generally, the Mg values reported in

Evaluating the effect of magnesium supplementation and cardiac arrhythmias after acute coronary syndrome: a systematic review and meta-analysis

“…Magnesium deficiency presents among about 71% of patients who underwent Cardiopulmonary bypass (CPB) [ 5 ]. In many studies intraoperative addition of the magnesium sulfate was beneficial.…”

Point Of Care Testing of Ionized Magnesium in Blood with Potentiometric Sensors - Opportunities and Challenges

“…Cobas® (Roche), Advia® (Siemens), Architect® (Abbott) and Synchron® (Beckman Coulter), they are not easily applied to POC testing applications, e.g., testing in ED, OR, ICU and ambulance environments. Recent clinical studies [3] demonstrated the association of hypomagnesemia and mortality rates [6] in ICU patients experiencing hemodialysis [18], type 2 diabetes [19], cardiovascular diseases [20], cardiovascular deaths, and medical surgical intensive care [21]. Monitoring and controlling iMg may be more relevant in patient care than TMg, especially when an abnormal protein concentration can be expected, as is often seen for critically ill patients [22,23].…”

Magnesium: Forgotten Mineral in Cardiovascular Biology and Atherogenesis

“…Six to sixty-fi ve percent of all hospitalized patients exhibit low serum Mg; patients with numerous cardiovascular disorders associated with atherogenesis demonstrate the most profound defi cits in body Mg. 3,[10][11][12][13][14][15][16][17][18][19][20][21] 22,23 Because the levels of anions can vary signifi cantly in pathological states, and in view of the role apparently played by Mg in cellular homeostasis (Table 19.2), it is desirable to directly measure free Mg 2+ in blood 24 and other body fl uids. With this aim in mind, Mg 2+ -sensitive electrodes have been designed to obtain these measurements in the presence of potential cationic interferences.…”