Magnesium flux caused by coronary artery bypass operation: three patterns of deficiency.

We undertook a study to evaluate the patterns of magnesium deficiency that may develop during and following coronary artery bypass operation without cardioplegia. In 18 patients intraoperative measurements of plasma magnesium and potassium concentrations and measurements of cardiac and skeletal muscle content of these ions were taken. The changes in plasma concentrations and excretion were evaluated postoperatively. Hemodilution at initiation of cardiopulmonary bypass caused a 17.3% decrease in plasma magnesium concentration (p < 0.01), which persisted until the first postoperative day. By the fifth postoperative day the level was 19.5% greater than the preoperative value. Urinary excretion of magnesium reflected changes in plasma magnesium concentration. Cardiac muscle content of magnesium decreased by 13.3%. Plasma potassium concentration was elevated by hemodilution (p < 0.01), and muscle potassium was not depleted. We conclude that three patterns of magnesium depletion occur: hemodilution, intraoperative cellular depletion, and postoperative cellular depletion. The findings support the need for magnesium supplementation during and after cardiac operation.