The purpose of the study was to analyse the effects of different forms of magnesium supplementation on its serum concentrations and the frequency of atrial fibrillation in patients undergoing coronary artery bypass graft surgery with extracorporeal circulation (ECC). One hundred and twenty adult patients were examined. All of them received intravenous infusions of MgSO4 during surgery and the early postoperative period (18 hours). Moreover, some of them received preoperative Mg supplementation. Therefore, patients were divided into six groups: A) patients, receiving an intravenous infusion 3.33 mg of MgSO4 per min; B) those receiving preoperative, oral Mg supplementation (OPS-Mg) and intravenous 3.33 mg of MgSO4 per min; C) patients receiving intravenous 6.66 mg of MgSO4 per min; D) patients receiving OPS-Mg and 6.66 mg of MgSO4 per min; E) patients receiving intravenous 10 mg of MgSO4 per min; F) those receiving OPS-Mg and 10 mg of MgSO4 per min. Additionally, all patients were divided into three groups: O (patients, who did not receive dopamine or dobutamine infusions), DOP (those receiving dopamine infusions in doses dependent on their clinical state) and DOB (those receiving dobutamine infusions in doses dependent on their clinical state). Total serum Mg concentrations (Mg(t)) were measured at five points: 1) 10 min before anaesthesia; 2) 10 min after ECC; 3) 10 min after surgery, 4) in the morning of postoperative day 1, 5) in the morning of postoperative day 2. The data were analyzed statistically; values at the first measurement points were considered as baseline. In group A, Mg(t) decreased at time points 2, 3, 4. Similar changes were observed in group B, however, in both groups Mg(t) returned to the baseline value at time point 5. In groups C and D, Mg(t) decreased at point 2 and 3, whereas in groups E and F it was increased during all the study period. The changes in Mg(t) were slightly less in patients receiving OPS-Mg, these patients had a significantly higher Mg(t) at time point 1. Mg(t) decreased in the O, DOP and DOB groups at measurement points 2 and 3. Moreover, the lowest Mg(t) was observed in the DOP group. Atrial fibrillation (AF) was noted in 33 patients (27.5%). The highest percentage of patients with AF during the early postoperative days was observed in groups A and B (45%). In groups C, D, E and F, AF was detected in 25%, 20%, 20% and 10% of patients, respectively. The incidence of AF was significantly higher in groups A and B compared to the other groups. Moreover, episodes of AF were rarer in patients receiving preoperative, oral Mg supplementation.
Conclusions: 1) ECC resulted in a decrease in Mg(t); 2) Mg infusion at the dose of 3.33 mg/min had little effect for the prevention of postoperative AF; 3) the infusion of 10 mg/min of MgSO4 maintained the level of Mg(t) during CABG and most effectively reduced AF; 4) OPS-Mg played a beneficial role in Mg(t) disturbances during CABG; 5) dopamine caused the most severe disturbances in serum Mg(t) concentration.