Changes of serum magnesium ions in open heart surgery.

The changes of magnesium in the serum were studied in 20 patients undergoing cardiac valve substitution procedures in extracorporeal circulation. The serum magnesium ions were determined before the onset of the anesthesia, at the beginning and at the end of the extracorporeal circulation, at the end of surgery and during the first post-operative day. A slight magnesium ion deficiency was observed even in the initial serum levels, probably due to the pre-operative diuretic therapy. The hypomagnesemia observed during the bypass was related to haemodilution and urinary losses. A limited increase in magnesemia, probably caused by the diffusion of the ion towards the vascular compartment, was observed at the end of the extracorporeal circulation. A new decrease was found during the post-operative stage, perhaps caused by the action of diuretics, which were administered.