When should serum magnesium be measured prior to non-cardiac surgery?

While prospective data is scant, the advisability of magnesium measurement appears to be convincing in selected circumstances. Electrolyte abnormalities, mainly hypokalemia and hypomagnesemia, are associated with an increased risk for developing cardiac arrhythmias, however, conflicting opinions remain. If performed on all patients undergoing non-cardiac surgery, magnesium measurement would add considerably to health care costs; however, if limited to patients identified as high risk by the above parameters, the additional cost per patient is in keeping with other standard tests. Given the low cost of testing and replacement, preoperative magnesium measurement appears reasonable in patients with structural heart disease, diabetes, chronic alcoholism, and chronic (loop) diuretic use. When high risk patients are undergoing high risk operations, the low cost of measurement and replacement appears particularly cost-effective, whether it reduces morbidity and prolonged hospitalization from atrial fibrillation or mortality from sustained ventricular arrhythmias. Until additional data becomes available, use of this simple test in patients likely to manifest hypomagnesemia who are at elevated risk of cardiac tachyarrhythmias and cardiac complications following non-cardiac surgery seems prudent.