Comparison between Continuous Infusion and Bolus Dose of Magnesium Sulfate on Left Ventricular Strain in Patients Undergoing Coronary Artery Bypass Grafting Surgery – A Prospective Randomized Double-blinded Study

Abstract Objective: The objective of this study was to compare the effects of continuous infusion and bolus administration of magnesium sulfate on left ventricular strain in patients undergoing coronary artery bypass grafting (CABG) surgery under cardiopulmonary bypass (CPB). Design: This was a prospective, randomized, double-blinded study. Setting: This study was conducted at a university-level tertiary referral cardiac care hospital. Participants: We enrolled 72 adult patients aged between 18 and 70 years undergoing elective CABG under CPB. Interventions: The study participants were randomized into the infusion group (Group I, n = 37) and the bolus group (Group B, n = 35). Group I patients received an infusion of magnesium sulfate at 10 mg/kg/h, initiated during induction of anesthesia, and continued until the end of surgery. Group B patients received a 50 mg/kg bolus of magnesium sulfate before the aortic cross-clamp was released during CPB. Measurements and Main Results: Primary objective parameters of global longitudinal strain (GLS) and global circumferential strain (GCS) were measured using transesophageal echocardiography. The secondary observations of the study were (1) vasoactive inotropic score (VIS), (2) serum lactate levels, (3) serum magnesium levels, (4) systemic vascular resistance index (SVRI) during CPB, (5) incidence of arrhythmias after aortic cross-clamp release, (6) duration of mechanical ventilation, and (7) length of intensive care unit (ICU) and hospital stay. The post-CPB GLS values were significantly less negative in Group B in comparison to Group I (−11.85% ±3.65% vs. −13.32% ±2.09%, P = 0.0383), whereas there was no significant difference in the post-CPB GCS values between the two groups. The serum lactate levels were significantly higher in Group B in comparison to the Group I at 60 min of CPB (2.38 ± 0.52 mmol/L vs. 1.81 ± 0.8 mmol/L, P = 0.0007): 90 min of CPB (2.78 ± 0.68 mmol/L vs. 1.92 ± 0.59 mmol/L, P = 0.0001) and in the post-CPB period (3.01 ± 0.59 mmol/L vs. 2.35 ± 0.89 mmol/L, P = 0.0004). On comparison of SVRI (dynes.sec.cm/m 2 ) between the two groups, it was significantly higher in Group B at 60 min (2285.29 ± 217.1 vs. 2177.43 ± 233.01, P = 0.0462) and in Group I at 90 min (2068.35 ± 125.75 vs. 1940.1 ± 199.48, P = 0.0016). The VIS was significantly less in Group I in comparison to Group B at different time points: after weaning from CPB (4.86 ± 2.28 vs. 7.11 ± 4.22, P = 0.0060), on ICU arrival (5.62 ± 2.02 vs. 7.86 ± 4.07, P = 0.0039), and at 6 h in ICU (5.35 ± 1.65 vs. 7.57 ± 4.29, P = 0.0046). The duration of mechanical ventilation admission was significantly less in Group A compared to Group B (9.86 ± 2.23 h vs. 11.6 ± 2.85 h, P = 0.0051). In contrast, the length of ICU and hospital stay was comparable between the two groups. Conclusion: The results suggest that administering magnesium sulfate as an infusion, rather than as a bolus, demonstrated a cardioprotective effect, as evidenced by the maintenance of higher post-CPB GLS values compared with bolus administration. Magnesium sulfate infusion is safe and effective in attenuating electromechanical effects, improving electrical stability, reducing the need for inotropic and vasopressor support, decreasing serum lactate concentrations during CPB, and shortening the duration of mechanical ventilation in the post-CPB period.