MAGNESIUM FLUX CAUSED BY CORONARY-ARTERY BYPASS OPERATION - 3 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 p lasma magnesium and potassium concentrations and measurements of cardi ac and skeletal muscle content of these ions were taken. The changes i n plasma concentrations and excretion were evaluated postoperatively. Hemodilution at initiation of cardiopulmonary bypass caused a 17.3% de crease in plasma magnesium concentration (p < 0.01), which persisted u ntil the first postoperative day. By the fifth postoperative day the l evel was 19.5% greater than the preoperative value. Urinary excretion of magnesium reflected changes in plasma magnesium concentration. Card iac muscle content of magnesium decreased by 13.3%. plasma potassium c oncentration was elevated by hemodilution (p < 0.01), and muscle potas sium was not depleted. We conclude that three patterns of magnesium de pletion occur: hemodilution, intraoperative cellular depletion, and po stoperative cellular depletion. The findings support the need for magn esium supplementation during and after cardiac operation.