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：急性肾损伤（acute kidney injury, AKI）的发生与创伤性脑损伤（traumatic brain injury, TBI）患者的死亡风险升高密切相关。本研究旨在探讨血清镁水平与创伤性脑损伤患者发生急性肾损伤的风险之间的关联。
方法：从2008-2019年的医疗信息集市重症监护Ⅳ数据库（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，评估入院时血清镁水平及住院期间血清镁变异系数（coefficient of variation, CV）与急性肾损伤风险的相关性，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）、脓毒症状态（否、是）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：纳入的991例患者中，140例（14.13%）在住院期间发生急性肾损伤。与血清镁水平为1.7~2.0 mg/dL（第2三分位组）的患者相比，血清镁水平≤1.7 mg/dL（第1三分位组）的患者急性肾损伤风险更高（OR=1.68，95%CI：1.01~2.81）；而血清镁水平>2.0 mg/dL（第3三分位组）的患者未观察到此类关联（P=0.479）。对于血清镁变异系数，与血清镁变异系数≤4%（第1三分位组）的患者相比，血清镁变异系数>10%（第3三分位组）的患者急性肾损伤风险升高（OR=2.26，95%CI：1.16~4.41）；血清镁变异系数为4%~10%（第2三分位组）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、非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%）与急性肾损伤风险升高相关（P<0.05）。
结论：创伤性脑损伤患者入院时较低的血清镁水平或住院期间较高的血清镁变异系数与急性肾损伤风险升高显著相关。