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

Background. To determine the changes in magnesaemia in cardiac surgical pat ients submitted to cardiopulmonary bypass (CPB) and their influence on peri operative morbidity, Methods, Setting: the cardiovascular surgery department of a university hos pital. Patients: 60 patients of both sexes, mean age 60 +/- 12 yrs, operate d on consecutively for myocardial revascularization or valve replacement. I nterventions: plasma Mg2+ levels were measured preoperatively, during CPB, postCPB and throughout the first 24 hrs after operation. Preoperative plasm a Mg2+ levels of these patients were compared with those of 15 non-cardiac surgical patients and 11 healthy volunteers, Results, Mean values of Mg2+ similar in the three populations although in t he group of cardiac patients the number of hypomagnesaemic patients was sig nificantly higher (16 patients=26.6%). In these 16 patients, pre operative hypomagnesaemia had a statistically significant relationship with the preop erative treatment with beta-blockers and previous history of arrhythmias (p <0.05). A progressive statistically significant decrease of Mg2+ was observ ed throughout the surgery that remained low at 24 hours postoperatively (p< 0.05). Normomagnesemic patients needed significantly more shocks and electr ical energy to obtain heart defibrillation after CPB. The incidence of both postoperative arrhythmias and postoperative low cardiac index (<2.5 L.m(2) ) was statistically significantly more frequent in hypomagnesaemic patients (p<0.05). Conclusions. Preoperative hypomagnesaemia was more frequent in this small s ample of cardiac surgical patients than in non-cardiac surgical patients an d was related to preoperative treatment with beta -blockers. Hypomagnesaemi a caused by CPB persisted 24 hrs after operation and was associated with hi gher incidence of both postoperative arrhythmias and low cardiac index.