Magnesium metabolism in open-heart surgery

The levels of magnesium in serum, urine and erythrocytes were studied in 22 patients undergoing cardiac surgery for valvular prosthesis. Magnesium values were correlated with serum albumin and non-esterified fatty acids (NEFA). Data were collected before anesthesia, 10 min after sternotomy, heparinization and declamping of the aorta and in the 1st postoperative day. A slight decrease in magnesemia was observed before extracorporeal circulation (ECC) and was mainly due to haemodilution. The correlation of magnesium with NEFA was significant only after heparinization. The use of the St Thomas solution as cardioplegia fully corrected the hypomagnesemia previously reported during ECC as well as in the 1st postoperative day. A moderate hypermagnesemia was observed at the end of ECC, but no patient reached dangerous levels of serum magnesium. Urinary losses increased during and after ECC. Red blood cell magnesium showed a slight increase before ECC, followed by a significant reduction at the end of ECC.