Magnesium administration has long been a standard protocol following cardioplegic arrest to prevent hypomagnesemia-related arrhythmias. However, with the widespread use of del Nido cardioplegia (dNC), which already contains magnesium, questions arise about whether additional supplementation remains necessary. This study, conducted at Cincinnati Children’s Hospital Medical Center (CCHMC), investigates serum magnesium levels before and after cardiopulmonary bypass (CPB) in 100 patients to determine if exogenous magnesium administration leads to hypermagnesemia.
Background and Rationale
Cardioplegic solutions like dNC are essential in pediatric and congenital cardiac surgery. Developed at the University of Pittsburgh, dNC is designed for the immature myocardium, offering extended ischemic protection. Unlike previous solutions like Mee cardioplegia, dNC contains magnesium, which helps reduce intracellular calcium accumulation and prevent myocardial stiffness post-bypass.
CCHMC switched from Mee cardioplegia to dNC in 2014 but continued administering magnesium post-cross-clamp removal at a dose of 25 mg/kg up to 1 g. Since dNC already contains magnesium, this study sought to determine if this practice was necessary or if it resulted in unintended hypermagnesemia.
Methods and Study Design
A prospective study was conducted between January 2022 and October 2023, enrolling 100 patients ranging from infants to adults undergoing CPB with dNC. Two blood samples were collected:
- Draw 1 (D1): Collected post-cardioplegia administration and 30 minutes before cross-clamp removal.
- Draw 2 (D2): Collected 10 ± 2 minutes after cross-clamp removal and post-magnesium administration.
These samples were analyzed at the CCHMC core laboratory, with normal serum magnesium reference values defined as 1.6–2.6 mg/dL. Statistical analysis was performed using the Wilcoxon rank sum test and paired t-tests.
Results: High Magnesium Levels Across the Board
Findings showed that magnesium levels remained elevated throughout CPB:
- D1 (Pre-Cross-Clamp Removal): Median magnesium level was 3.0 mg/dL (mean 3.22 mg/dL), well above the upper normal limit. Statistical significance was achieved (p < 0.001).
- D2 (Post-Cross-Clamp Removal & Magnesium Administration): Median level was 4.0 mg/dL (mean 4.8 mg/dL), with 99 out of 100 patients exhibiting hypermagnesemia. Though statistical significance wasn’t reached (p = 0.089), nearly all cases exceeded normal magnesium levels.
Age-based analysis revealed consistent trends, confirming that additional magnesium administration was unnecessary across all pediatric and adult groups.
Discussion: Implications for Clinical Practice
The findings strongly suggest that routine magnesium supplementation following dNC cardioplegia may be unnecessary. While prior studies linked magnesium deficiency to postoperative arrhythmias and poor myocardial function, these studies did not use magnesium-based cardioplegic solutions like dNC. The excessive magnesium levels observed in this study raise concerns about hypermagnesemia’s risks, including:
- Arrhythmias (ironically, the very complication magnesium is meant to prevent)
- Hypotension
- Neuromuscular depression
Given these risks, the study recommends discontinuing routine magnesium administration post-cross-clamp removal when dNC is used. Future research should explore whether adjusting magnesium levels in dNC could further optimize outcomes.
Conclusion
This study highlights the importance of reevaluating clinical practices following changes in cardioplegic solutions. The historical practice of magnesium administration post-CPB, originally necessary with Mee solution, no longer appears justified with dNC. Eliminating this step could reduce the risk of hypermagnesemia and its associated complications, ultimately improving patient outcomes.
Study Ranking: 4 (High Quality) This study is based on a well-structured prospective design with 100 patients. While not a double-blind randomized trial, it provides strong evidence supporting a significant clinical change.
