Association between magnesium sulfate use and acute kidney injury in patients undergoing cardiac surgery: a retrospective cohort study

Postoperative magnesium administration reduces atrial fibrillation risk, but its impact on renal function remains controversial. This retrospective study evaluated the independent association between early postoperative magnesium sulfate infusion and acute kidney injury (AKI) in cardiac surgery patients. We included adults with hypomagnesemia or normomagnesemia post-cardiac surgery. The primary exposure was intravenous magnesium use within 7 postoperative days (strictly prior to AKI onset). The primary outcome was severe AKI (KDIGO grade 2–3). Double robust analysis assessed the independent association between magnesium exposure and AKI, while machine learning models ranked predictor importance. Among 4,992 enrolled patients, double robust analysis revealed that magnesium use was independently associated with a higher incidence of severe AKI (propensity score-matched incidences: 52.4% vs. 48.7%; robust OR = 1.18, 95% CI 1.03–1.34, p = 0.02), consistent across sensitivity analyses. Machine learning identified baseline heart failure and prior kidney disease as the strongest AKI predictors. In conclusion, postoperative magnesium sulfate use is independently associated with an increased incidence of severe AKI after cardiac surgery. Magnesium supplementation warrants caution, particularly in high-risk patients with preexisting cardiac or renal insufficiency.