Sustained postoperative elevation of ionized magnesium levels following cardiac surgery with magnesium-enriched cardioplegia: a prospective observational study.

This study aimed to clarify perioperative changes in ionized magnesium levels (iMg), a physiologically active fraction, and particularly the persistence of hypermagnesemia at the time of extubation in cardiac surgery using magnesium-enriched cardioplegia. We conducted a prospective observational study of 48 patients undergoing elective cardiac surgery. iMg was measured at three time points: induction of anesthesia, intensive care unit (ICU) admission, and extubation. The median duration of postoperative mechanical ventilation was 17 h. iMg increased markedly to 1.49 [1.23-1.85] mmol/L at ICU admission and remained significantly elevated at extubation (0.97 [0.80-1.14] mmol/L), exceeding the physiological reference value in 46 patients (96%). Correlation analysis demonstrated a moderate positive correlation between total cardioplegia volume and iMg at ICU admission (r = 0.549), whereas this association was no longer significant at extubation. To the best of our knowledge, this study is the first to demonstrate, using direct measurement of physiologically active iMg, that hypermagnesemia due to exogenous magnesium loading from magnesium-enriched cardioplegia can persist until the phase of ventilator weaning. Perioperative magnesium kinetics in cardiac surgery are difficult to predict accurately owing to the complex interactions among multiple perioperative factors. Monitoring iMg provides clinicians with essential information regarding the actual physiological magnesium status, which may serve as a supportive guide for avoiding unnecessary magnesium supplementation.