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.