Supplementary Material for: Association between serum magnesium levels and risk of acute kidney injury in patients with traumatic brain injury: A retrospective cohort study from the MIMIC-Ⅳ database

Introduction: The occurrence of acute kidney injury (AKI) is associated with a higher risk of mortality in patients with traumatic brain injury (TBI). This study aimed to explore the relationship between serum magnesium levels and the risk of AKI in patients with TBI.
Methods: Patients with TBI were identified from the Medical Information Mart Intensive Care Ⅳ (MIMIC-Ⅳ) 2008-2019. The relationship between serum magnesium levels at admission and magnesium coefficient of variation (CV) during hospitalization and the risk of AKI was analyzed using multivariable logistic regression analysis and expressed as odds ratio (OR) and 95% confidence interval (CI). Subgroup analyses were performed according to Glasgow Coma Scale (GCS) score (<14, ≥14), sepsis (no, yes), and estimated glomerular filtration rate (eGFR; <60, ≥60).
Results: Of the 991 patients included, 140 (14.13%) developed AKI during hospitalization. Patients with magnesium levels ≤1.7 mg/dL (tertile 1) (OR=1.68, 95%CI: 1.01-2.81) were associated with a higher risk of AKI compared to those with magnesium levels of 1.7-2.0 mg/dL (tertile 2), but no association was found in those with magnesium levels >2.0 mg/dL (tertile 3) (P=0.479). For magnesium CV, patients with magnesium CV >10% (tertile 3) (OR=2.26, 95%CI: 1.16-4.41) were linked to an increased risk of AKI compared to those with magnesium CV ≤4% (tertile 1), but there may be a slight association between magnesium CV of 4%-10% (tertile 2) and AKI risk (OR=1.86, 95%CI: 0.99-3.48; P=0.053). Subgroup analyses showed that lower magnesium levels (≤1.7 mg/dL) or greater magnesium CV (>10%) were associated with a higher risk of AKI only in patients with a GCS score ≥14, non-sepsis, or eGFR ≥60 mL/min/per1.73m2 (P<0.05).
Conclusion: Lower serum magnesium levels at admission or greater magnesium CV during hospitalization were associated with a higher risk of AKI in patients with TBI.

引言：创伤性脑损伤（traumatic brain injury, TBI）患者并发急性肾损伤（acute kidney injury, AKI）时，其死亡风险显著升高。本研究旨在探讨创伤性脑损伤患者的血清镁水平与急性肾损伤发病风险之间的关联。
方法：本研究从2008-2019年的医学信息共享重症监护数据库Ⅳ（Medical Information Mart Intensive Care Ⅳ, MIMIC-Ⅳ）中筛选创伤性脑损伤患者。采用多变量logistic回归分析，探讨入院时血清镁水平、住院期间血清镁变异系数（coefficient of variation, CV）与急性肾损伤发病风险之间的关联，结果以比值比（odds ratio, OR）及95%置信区间（confidence interval, CI）表示。根据格拉斯哥昏迷量表（Glasgow Coma Scale, GCS）评分（<14分、≥14分）、是否合并脓毒症（否、是）以及估算肾小球滤过率（estimated glomerular filtration rate, eGFR；<60 mL/min/1.73m²、≥60 mL/min/1.73m²）进行亚组分析。
结果：本研究共纳入991例患者，其中140例（14.13%）在住院期间发生急性肾损伤。与血清镁水平处于1.7~2.0 mg/dL（第二三分位组）的患者相比，血清镁水平≤1.7 mg/dL（第一三分位组）的患者急性肾损伤发病风险更高（OR=1.68，95%CI：1.01~2.81）；而血清镁水平>2.0 mg/dL（第三三分位组）的患者未观察到此类关联（P=0.479）。就血清镁变异系数而言，与变异系数≤4%（第一三分位组）的患者相比，变异系数>10%（第三三分位组）的患者急性肾损伤发病风险显著升高（OR=2.26，95%CI：1.16~4.41）；变异系数处于4%~10%（第二三分位组）的患者与急性肾损伤风险可能存在轻度关联（OR=1.86，95%CI：0.99~3.48；P=0.053）。亚组分析显示，仅在格拉斯哥昏迷量表评分≥14分、未合并脓毒症或估算肾小球滤过率≥60 mL/min/1.73m²的患者中，较低的血清镁水平（≤1.7 mg/dL）或较高的血清镁变异系数（>10%）与急性肾损伤发病风险升高显著相关（P<0.05）。
结论：创伤性脑损伤患者入院时血清镁水平较低，或住院期间血清镁变异系数较高，均与急性肾损伤发病风险升高显著相关。