Bioimpedance analysis versus lung ultrasonography for optimal risk prediction in hemodialysis patients

Fluid overload is associated with adverse outcomes in hemodialysis (HD) patients. Two bedside methods are increasingly utilized to evaluate objectively fluid status-bioimpedance and lung ultrasonography, but there is no available direct, head-to-head comparison of their prognostic significance. Importantly, their predictive abilities have never been tested in a HD population, alongside those of a classic model that also incorporates established echocardiographic parameters of increased mortality risk. Between 26 May 2011 and 26 October 2012, we included in the study 173 patients undergoing chronic HD treatment for at least 3 months in a single dialysis unit. Relative fluid overload (RFO) and B-lines score (BLS) were used as candidate predictors. From Cox survival analysis we evaluated the increase in the predictive abilities for all-cause mortality of adding continuous RFO or BLS to a model including conventional predictors . 31 patients (17.9 %) died during a median follow-up of 21.3 (interquartile range 19.9-30.3) months. All Cox models showed good calibration. The C statistic for the all-cause mortality prediction increased significantly when the RFO was included into the baseline model (ΔC statistics 0.058 95 %CI = 0.003-0.114), but not when the BLS was included into the baseline model. Only the model that incorporated RFO showed significantly better risk reclassification abilities than the baseline model (IDI = 3.6 % and continuous NRI = 24.8 %). Fluid overload, as assessed by bioimpedance, and not by lung ultrasonography, improves risk prediction for death, beyond classical and echocardiographic-based risk prediction scores/parameters.