Thoracic versus whole body bioimpedance: association between resistance ratio and central and peripheral fluid status in chronic kidney patients, a cohort study

Background: Fluid overload in non-dialysis chronic kidney disease (CKD) increases the risk of cardiovascular disease and all-cause mortality, and its assessment remains challenging. Although whole body bioimpedance can guide fluid status assessment, it faces several limitations. Bioimpedance measurements of the thoracic segment could offer an alternative. This study investigated the relationship between parameters of fluid overload in non-dialysis CKD patients and both bioimpedance applications. Additionally, the predictive role of bioimpedance in renal replacement therapy was explored. Methods: Thoracic and whole body bioimpedance measurements were obtained in non-dialysis stage 3b-5 CKD patients. The association between the resistance ratio (160 kHz / 8 kHz) and clinical and laboratory markers of fluid overload and echocardiographic parameters was assessed via correlation analysis. Kaplan-Meier analysis was performed to estimate the probability of renal replacement therapy during a two-year follow up. Results: In total, 71 patients were included. Mean age was 73 ± 11 years, and 58 % were men. Mean resistance ratios were 0.82 ± 0.09 for thoracic and 0.86 ± 0.02 for whole body measurements. Thoracic resistance ratio correlated significantly with the IVCCI (r=-0.424, P=0.007), whereas whole body resistance ratio did not. Whereas thoracic resistance ratio was not correlated with other parameters of fluid overload, whole body resistance ratio was correlated with complaints of fluid overload (rbp = 0.294, P = 0.018), peripheral edema (rbp = 0.395, P = 0.001) and pro-BNP (rs = 0.612, P < 0.001). There was no correlation between the resistance ratios and echocardiographic parameters. Whole body resistance ratio was associated with the initiation of renal replacement therapy (X2 = 3.992, P = 0.046), whereas thoracic resistance ratio was not. Conclusion: This study presents a novel wearable thoracic bioimpedance device to assess fluid status in non-dialysis CKD patients. Thoracic resistance ratio may provide additional insight in fluid status in the central volume compartments in addition to whole body bioimpedance but does not seem to act as a replacement. The integration of thoracic and whole-body bioimpedance with current clinical assessment methods deserves further study.