[Changes in plasma and urinary calcium levels during cardiopulmonary bypass]

Plasma total protein, total calcium, ionized calcium and urinary calcium were measured in six patients scheduled for open heart surgery, and the effect of the administration of calcium during and after cardiopulmonary bypass (CPB) was studied. After the initiation of CPB, plasma total protein decreased significantly from 5.47 +/- 0.50 g.dl-1 to 2.55 +/- 0.23 g.dl-1 (P < 0.01). Total calcium also decreased from 2.14 +/- 0.29 mmol.l-1 to 1.38 +/- 0.07 mmol.l-1 (P < 0.01), and remained depressed during CPB. However, ionized calcium was not decreased and showed normal value during CPB because total protein concentration was decreased by hemodilution. Urinary calcium excretion increased gradually during CPB from 0.18 +/- 0.17 mmol.h-1 to 0.87 +/- 0.38 mmol.h-1 (P < 0.01) and the increase continued after CPB. Fractional excretion of filtered calcium increased from 0.85 +/- 0.63% to 54.16 +/- 36.52% (P < 0.05) accompanied with hypothermia. From these findings, reabsorption of the calcium in the kidney was thought to be inhibited by the influence of hypothermia at the early phases after weaning from CPB. When total protein returned to normal value after weaning from CPB, percentage of ionized calcium is predicted to diminish. We conclude that after weaning from CPB, administration of calcium is required because of the prolonged increase of urinary calcium excretion, particularly if blood containing citrate is given.