Con: Magnesium should not be administered to all coronary artery bypass graft surgery patients undergoing cardiopulmonary bypass

Evaluating the need for magnesium administration following cardioplegic arrest with del Nido cardioplegia solution

BACKGROUND

del Nido cardioplegia (dNC) solution is widely used in pediatric and congenital cardiac surgery. In 2014, Cincinnati Children's Hospital Medical Center (CCHMC) changed from Mee cardioplegic solution to dNC. Since Mee solution does not contain magnesium, magnesium was administrated post cross-clamp removal, at a dose of 25 mg/kg up to 1 g, to abate hypomagnesemia. This practice remained in place with the use of dNC. We postulated that patients may experience hypermagnesemia under this protocol.

METHODS

To determine if exogenous magnesium is necessary post-clamp removal in our practice, a study examining serum magnesium levels during cardiopulmonary bypass (CPB) was completed from January 2022 through October 2023 (IRB #2021-0816). One hundred patients undergoing CPB with cross-clamp, ranging from infants to adults, were consented. Two magnesium samples were collected. Draw 1 (D1) was collected post cardioplegia administration and 30 min prior to cross-clamp removal. Draw 2 (D2) was collected post-cross-clamp removal and 10 ± 2 min following magnesium administration.

RESULTS

Both samples demonstrated magnesium levels > 1.6 mg/dL or higher (normal magnesium range at CCHMC, 1.6-2.6 mg/dL). A Wilcoxon rank sum test demonstrated statistical significance for D1, comparing the number of samples that fell above 2.6 mg/dL vs. those that fell within the normal range (p < 0.001). D2 demonstrated values above the normal range for all but one sample, which does not satisfy the criteria of the Wilcoxon rank sum test for demonstrating significance (p = 0.089); however, ninety-nine samples displayed hypermagnesemia.

CONCLUSION

This study demonstrates that exogenous magnesium administration may not be necessary in the setting of our practice at CCHMC and dNC cardioplegic arrest.

Does magnesium-supplemented cardioplegia reduce cardiac injury? A meta-analysis of randomized controlled trials

BACKGROUND

Magnesium is often used to supplement cardioplegic solutions during cardiopulmonary bypass due to its cardioprotective effect during ischemia and reperfusion. The aim of this meta-analysis was to evaluate the effects of magnesium-supplemented cardioplegia versus an inactive (placebo) control cardioplegia on reducing cardiac injury after cardiac arrest surgery, as found by randomized, controlled trials.

METHODS

The Medline, Cochrane Library, and Chinese literature databases (CJFD, CBM, CSJD, Wanfang) were comprehensively searched for reports of randomized, controlled trials (RCTs) evaluating magnesium-supplemented cardioplegic solutions. The clinical parameters and outcomes of interest were the incidence of postoperative low cardiac output, auto-rebeating rate, ICU stay length, new onset postoperative atrial fibrillation, peak value of CK-MB (and/or cTnI), incidence of myocardial infarction, and in-hospital mortality.

RESULTS

Ten trials, with a total of 1214 patients, were included. The frequency of low cardiac output, inotropic utilization, and myocardial infarction, as well as auto-rebeating rate, length of ICU stay and in-hospital mortality, were similar between the two groups. There was a marginal reduction in the incidence of new-onset postoperative atrial fibrillation in the magnesium-supplemented cardioplegia group.

CONCLUSIONS

The advantage of magnesium-supplemented cardioplegia, compared with cardioplegia without magnesium, remains unconvincing based on the current evidence. The decision to add magnesium to the cardioplegic solution to a patient undergoing cardiac arrest surgery should be carefully considered.

Magnesium-supplemented warm blood cardioplegia in patients undergoing coronary artery revascularization

BACKGROUND

Although there is growing evidence to suggest that the administration of magnesium (Mg2+) to patients undergoing coronary artery bypass grafting (CABG) and to patients after myocardial infarction is beneficial, the addition of Mg2+ to cardioplegic solutions remains controversial. The aim of this study was to compare the effects of intermittent warm blood cardioplegia with and without Mg2+ supplementation on the early postoperative clinical outcomes in patients undergoing both elective or urgent CABG.

METHODS

Four hundred patients undergoing CABG were prospectively randomized to receive either blood cardioplegia without Mg2+ (BC, n = 200) or supplemented with Mg2+ (BC-Mg2+, n = 200). Serial plasma Mg2+ concentrations were recorded at base line and postoperatively from days 1 to 4.

RESULTS

Patient characteristics were similar and no significant differences were found in early mortality and morbidity in the two groups. Analysis of 178 patients undergoing urgent CABG for unstable symptoms (BC = 95, BC-Mg2+ = 83) demonstrated a significantly lower requirement for internal defibrillation and temporary epicardial pacing in the BC-Mg2+ group. Furthermore, there was a nearly twofold lower incidence of new postoperative atrial fibrillation in the BC-Mg2+ group compared with the BC group (19% versus 34%, p = 0.03). Postoperative plasma Mg2+ levels were consistently lower in those patients who developed new postoperative atrial fibrillation compared with those who did not (p = 0.05).

CONCLUSIONS

The addition of Mg2+ to warm blood cardioplegia resulted in a lower incidence of intraoperative and postoperative arrhythmias in patients undergoing urgent CABG for unstable angina.