Are Currently Used Bioimpedance Methods in Hemodialysis Comparable for Calculating Dialysis Dose?

Bioelectrical impedance analysis has increasingly been incorporated into hemodialysis units (HD) as a useful, noninvasive technique for evaluating overall fluid status. The aims of this study were to verify whether the information obtained from two different bioelectrical impedance analysis methods (spectroscopy bioimpedance [BCM] and single-frequency bioelectric impedance vector analysis [SF-BIVA]) was comparable for analyzing fluid status, and to determine their impact when used to calculate dialysis dose. This observational cross-sectional study included 78 HD patients who underwent one measurement with BCM and one with SF-BIVA in the same dialysis session. For calculating the dialysis dose, total body water or urea distribution volume (V) was calculated by the Watson formula and compared with the V obtained from the two devices. The difference in V between the two devices was 5.4 L (P < 0.001). Given the existent correlation between V_BCM and V_SF-BIVA , we were able to apply a formula (corrected V = V_SF-BIVA = 1.04 × V_BCM + 4.85, r = 0.93), allowing comparison of the two bioimpedance methods. The mean dialysis dose for BCM device (Kt_ID /V_BCM ) was 2.49 ± 0.85, much higher than Kt_ID /V_SF-BIVA (2.06 ± 0.72) mainly due to the V obtained with the different devices, with Kt_ID /V_Watson being 2.03 ± 0.67. The results on volume distribution showed an acceptable correlation but the devices were not comparable due to intermethod differences observed. Dialysis centers using SF-BIVA will obtain much lower dialysis dose, but by applying our formula, the Kt/V would resemble that obtained by the BCM device.