Plasma digoxin and magnesium concentration in open heart surgery.

Plasma concentrations of various parameters were determined before, during and for 24 hours after cardiopulmonary bypass surgery in 12 patients. Digoxin levels decreased uniformly during perfusion in all cases. Plasma magnesium levels decreased significantly during pump and remained low for 24 hours. Potassium and calcium levels were kept in the high normal range as a result of exogenous administration of these ions. Small amounts of magnesium added to the circuit in 7 patients did not change the pattern of hypomagnesemia. More vigorous magnesium replacement during bypass surgery may be required if hypomagnesemia is to be avoided.