Preoperative Ionized Magnesium Levels and Risk of Acute Kidney Injury After Cardiac Surgery

Abstract

Rationale & objective: Although postoperative acute kidney injury (AKI) is a serious complication after cardiac surgery, preventive measures are limited. Despite the known association of preoperative low magnesium levels with cardiac surgery-related atrial fibrillation, the association between preoperative magnesium concentration and postoperative AKI has not been fully elucidated. This study evaluated the association between preoperative serum magnesium level and the development of AKI after cardiac surgery.

Study design: Retrospective observational cohort study.

Setting & participants: Patients aged≥18 years who underwent cardiac surgery at 2 South Korean tertiary hospitals between 2006 and 2020 were identified from medical records. Patients with missing information, an estimated glomerular filtration rate<15mL/min/1.73m², receiving maintenance dialysis, or a history of AKI treated by dialysis within 1 year before surgery were excluded.

Exposure: Preoperative serum magnesium levels.

Outcome: Postoperative AKI within 48 hours after surgery, defined using the Acute Kidney Injury Network (AKIN) criteria, and dialysis-treated AKI within 30 days after surgery.

Analytical approach: Multivariable logistic regression analysis.

Results: Among the 9,766 patients (median age, 64.0 years; 60.1% male), postoperative AKI and dialysis-treated AKI were observed in 40.1% and 4.3% patients, respectively. Postoperative AKI was more prevalent in patients with lower serum magnesium levels (44.9%, 41.4%, 39.4%, and 34.8% in quartiles 1-4, respectively). Multivariable logistic regression analysis revealed that the odds ratios (ORs) for postoperative AKI were progressively larger across progressively lower quartiles of serum magnesium concentration (adjusted ORs of 1.53 [95% CI, 1.33-1.76], 1.29 [95% CI, 1.12-1.48], 1.15 [95% CI, 1.01-1.31] for quartiles 1-3, respectively, relative to quartile 4, P for trend<0.001). Preoperative hypomagnesemia (serum magnesium level<1.09mg/dL) was also significantly associated with AKI (adjusted OR, 1.39 [95% CI, 1.10-1.77]) and dialysis-treated AKI (adjusted OR, 1.67 [95% CI, 1.02-2.72]).

Limitations: Causality could not be evaluated in this observational study.

Conclusions: Lower serum magnesium levels were associated with a higher incidence of AKI in patients undergoing cardiac surgery.

Keywords: Acute kidney injury (AKI); cardiac surgery; cardiac surgery-associated AKI (CSA-AKI); coronary artery bypass grafting (CABG); hypomagnesemia; magnesium; modifiable risk factor; open-heart valve repair; preoperative serum magnesium; renal function.