C . W . Striker and J . A . Reagor : J Extra Corpor Technol 2025 , 57 , 9 – 13 11
Table 3 . Study sample schedule .
Magnesium sample |
Sample time |
1 mL blood removed via CPB circuit |
30 min prior to cross-clamp removal and MgSO 4 dose ( Draw 1 ) |
1 mL blood removed via CPB circuit |
10 ± 2 min after cross-clamp removal and MgSO 4 dose ( Draw 2 ) |
The first sample , Draw 1 ( D1 ), was collected after cardioplegia administration and 30 min prior to cross-clamp removal . The second sample , Draw 2 ( D2 ), was collected after cross-clamp removal and 10 ± 2 min after magnesium administration . Each sample , approximately 2 mL , was collected in a light green top tube and sent to the core lab at CCHMC for analysis . Table 3 illustrates the schedule of procedures for this study .
Data collection
Magnesium levels were recorded on study-specific Case Report Forms ( CRFs ) and recorded in a RedCap ( Vanderbilt University , Nashville , TN ) database developed and maintained for the purpose of this study . Cross-clamp and magnesium administration times were collected during the normal clinical routine for patients undergoing congenital cardiac surgery with CPB . These data were electronically transmitted to the VISION ( Spectrum Medical , Fort Mill , SC , USA ) database . Data was secured in the password-protected RedCap and VISION database located within the CCHMC network during the study . The specific data contained in the VISION database was electronically harvested and submitted to the data management team for cleaning and correlation with data in the RedCap database .
Figure 1 . Draw 1 magnesium values grouped by those falling in the normal range of 1.6 – 2.6 mg / dL and greater than 2.6 mg / dL .
Measures Magnesium levels were analyzed and compared against normally expected values . The normal expected value of blood serum magnesium is 1.60 – 2.60 mg / dL , per CCHMC lab reference values .
Statistical analysis
The magnesium levels and cross-clamp times were described using medians and interquartile range ( IQR ). A Wilcoxon rank sum test was used to assess the difference in the magnesium levels between the magnesium ranges before and after magnesium administration , respectively . A paired t-test was used to estimate the difference in magnesium levels before and after the magnesium administration . Two-sided p-values < 0.05 were considered statistically significant . All statistical analyses were performed using R version 4.3.1 statistical software ( R Core Team , 2020 , Vienna , Austria ).
Results
Magnesium levels for D1 , prior to cross-clamp removal , and D2 , post magnesium administration are shown in Figures 1 and 2 . No magnesium levels fell below 1.6 mg / dL , the low end of normal . Median and mean values for D1 were 3.0 and 3.22 respectively , well above the top end of the 2.6 mg / dL normal
Figure 2 . Draw 2 magnesium values grouped by those falling in the normal range of 1.6 – 2.6 mg / dL and greater than 2.6 mg / dL .
range . 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 ). The median and mean values for D2 were 4.0 and 4.8 mg / dL respectively , with only one value falling in the normal range . 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