800: Evaluating Serum Magnesium Response and Its Predictors After Iv Magnesium in Critically Ill Patients

Introduction: Although intravenous magnesium sulfate (IV-MgSO₄) is frequently used in critically ill patients, real-world data evaluating its effectiveness are limited. We aimed to evaluate the serum magnesium response to IV-MgSO₄ and to identify predictors of a greater response in critically ill patients. Methods: This retrospective multicenter study included adult critically ill patients from the MIMIC-IV and eICU databases. Patients were included if they received IV-MgSO₄ and had serum magnesium measured within 36 hours before and after administration. Patients with end-stage renal disease and those receiving total parenteral nutrition or oral magnesium were excluded. The increase in serum magnesium per 1 gm of IV-MgSO₄ was assessed for the entire cohort and stratified by initial magnesium levels (normal, mild-to-moderate, and severe hypomagnesemia). Linear regression analyses were performed to identify predictors of greater magnesium response Results: The study included 25,637 critically ill patients who received 54,556 IV-MgSO₄ replacement episodes during their ICU stay. The mean age was 62.8 ±16.5(SD) years, and 13,180 (51.4%) were females. The most common ICU admission diagnoses were cardiovascular (n=7,399; 28.9%) and respiratory (n= 4,245; 16.6%). Baseline magnesium levels were normal in 39,149 (71.8%) episodes, mild-to-moderate hypomagnesemia in 13,588 (24.9%), and severe hypomagnesemia in 1,819 (3.3%). The median serum magnesium increased by 0.15 mg/dL (IQR: 0.05–0.25) per 1 gm IV-MgSO₄. The greatest increase was observed in patients with severe hypomagnesemia prior to administration of IV-MgSO₄(median [IQR]: 0.25 [0.15-0.50]), followed by mild-to-moderate hypomagnesemia (median increase 0.22 mg/dL, IQR:0.10-0.40) and normal serum magnesium (median increase 0.10 mg/dL, IQR:0.04-0.20) (p< 0.001). Predictors of higher response to IV-MgSO₄ were lower initial magnesium (β= 0.2080; 95%CI: 0.193 to 0.218; p< 0.001) and reduced renal function (β= 0.2058; 95%CI: 0.163 to 0.249; p< 0.001). Conclusions: Among a large cohort of critically ill patients, 1 gram of IV magnesium sulfate was associated with a median serum magnesium increase of 0.15 mg/dL, with greater responses in those with severe hypomagnesemia. Lower initial magnesium and reduced renal function were predictors of a greater magnesium response.