Supplementary Material for: Brain Natriuretic Peptide and Body Fluid Composition in Patients with Chronic Kidney Disease: A Cross-Sectional Study to Evaluate the Relationship between Volume Overload and Malnutrition

Background/Aim: Fluid volume overload occurs in chronic kidney disease (CKD), leading to the compensatory release of natriuretic peptides. However, the elevated cardiac peptides may also be associated with malnutrition as well as volume overload. Methods: Body fluid composition was measured in 147 patients with CKD between 2009 and 2015, and its relationship to brain natriuretic peptide (BNP) levels was examined. Body fluid composition was separated into three components: (a) a water-free mass consisting of muscle, fat, and minerals; (b) intracellular water (ICW) content, and (c) extracellular water (ECW) content. Excess fluid mass was calculated using Chamney's formula. Results: The measured BNP levels in the tertile groups were 10.9 ± 5.4, 36.3 ± 12.5, and 393 ± 542 pg/ml, respectively. Patients in a higher log-transformed BNP level tertile were more likely to be older, to have a higher frequency of cardiac comorbidities, pulse pressure, C-reactive protein levels, and proteinuria, and to have lower serum sodium, kidney function, and serum albumin (p < 0.05). In body fluid composition, decreased body mass was significantly associated with the ECW-to-ICW ratio in relation to the downward ICW slope (r = -0.235, p = 0.004) and was strongly correlated with excess fluid mass (r = -0.701, p < 0.001). The ECW-to-ICW ratio and excess fluid mass was independently associated with the BNP levels. Conclusion: Fluid volume imbalance between intra- and extracellular water regulated by decreased cell mass was independently associated with BNP levels, which may explain the reserve capacity for fluid accumulation in patients with CKD.

背景/研究目的：慢性肾脏病（CKD）患者可出现体液超负荷，进而代偿性释放利钠肽。然而，升高的心脏利钠肽或同时与营养不良及体液超负荷相关。
方法：于2009至2015年间，纳入147例慢性肾脏病（CKD）患者，检测其体液成分并分析其与脑利钠肽（BNP）水平的相关性。体液成分分为三部分：(a) 由肌肉、脂肪及矿物质构成的无水分成分；(b) 细胞内液（ICW）含量；(c) 细胞外液（ECW）含量。采用Chamney公式计算体液过剩量。
结果：三分位组的实测脑利钠肽（BNP）水平分别为10.9±5.4、36.3±12.5及393±542 pg/ml。高对数转换后BNP水平三分位组的患者年龄更大，心脏合并症发生率、脉压、C反应蛋白水平及蛋白尿发生率更高，而血清钠、肾功能及血清白蛋白水平更低（p < 0.05）。在体液成分方面，体质量下降与细胞外液/细胞内液比值显著相关，且与细胞内液下降斜率相关（r = -0.235, p = 0.004），同时与体液过剩量呈强相关（r = -0.701, p < 0.001）。细胞外液/细胞内液比值及体液过剩量均与脑利钠肽（BNP）水平独立相关。
结论：细胞量减少所调控的细胞内、外液间体液失衡与脑利钠肽（BNP）水平独立相关，这或可解释慢性肾脏病（CKD）患者体液蓄积的储备能力。