Plasma magnesium in patients submitted to cardiac surgery and its influence on perioperative morbidity

To determine the changes in magnesaemia in cardiac surgical patients submitted to cardiopulmonary bypass (CPB) and their influence on perioperative morbidity.

the cardiovascular surgery department of a university hospital.

60 patients of both sexes, mean age 60+/-12 yrs, operated on consecutively for myocardial revascularization or valve replacement.

plasma Mg2+ levels were measured preoperatively, during CPB, postCPB and throughout the first 24 hrs after operation. Preoperative plasma Mg2+ levels of these patients were compared with those of 15 non-cardiac surgical patients and 11 healthy volunteers.

Mean values of Mg2+ similar in the three populations although in the group of cardiac patients the number of hypomagnesaemic patients was significantly higher (16 patients=26.6%). In these 16 patients, preoperative hypomagnesaemia had a statistically significant relationship with the preoperative treatment with beta-blockers and previous history of arrhythmias (p<0.05). A progressive statistically significant decrease of Mg2+ was observed throughout the surgery that remained low at 24 hours postoperatively (p<0.05). Normomagnesemic patients needed significantly more shocks and electrical energy to obtain heart defibrillation after CPB. The incidence of both postoperative arrhythmias and postoperative low cardiac index (<2.5 L.m2) was statistically significantly more frequent in hypomagnesaemic patients (p<0.05).

Preoperative hypomagnesaemia was more frequent in this small sample of cardiac surgical patients than in non-cardiac surgical patients and was related to preoperative treatment with b-blockers. Hypomagne-saemia caused by CPB persisted 24 hrs after operation and was associated with higher incidence of both postoperative arrhythmias and low cardiac index.