Role of bioimpedance spectroscopy in assessment of body water compartments in hemodialysis patients.

Bioimpedance spectroscopy (BIS) has been advocated as a tool to assess fluid status in hemodialysis (HD) patients. However, uncertainty remains about the reliability of BIS in patients with abnormalities in fluid status. Aims of the study are to assess the agreement between total-body water (TBW) and extracellular volume (ECW) measured by BIS and tracer dilution (deuterium oxide [D(2)O] and sodium bromide [NaBr]), the influence of the relative magnitude of water compartments (expressed as TBW(D(2)O) and ECW(NaBr):body weight) on the agreement between BIS and tracer dilution, and the ability of BIS to predict acute changes in fluid status. BIS and tracer dilution techniques were performed in 17 HD patients before a dialysis session. Moreover, the relation between BIS and gravimetric weight changes was assessed during both isolated ultrafiltration and HD. Correlation coefficients between TBW and ECW measured by BIS and tracer dilution were r = 0.71 and r = 0.71, respectively. Mean differences (tracer-BIS) were 6.9 L (limits of agreement, -1.5 to 21.6 L) for TBW and 2.3 L (limits of agreement, -1.7 to 9.7 L) for ECW. There was a significant relationship between the relative magnitude of TBW and ECW compartments and disagreement between BIS and tracer dilution (r = 0.65 and r = 0.77; P < 0.05). During both isolated ultrafiltration and HD, there was a significant relation between gravimetric changes and change in ECW(BIS) (r = 0.83 and r = 0.76; P < 0.05), but not with change in TBW(BIS). In conclusion, agreement between BIS and tracer dilution techniques in the assessment of TBW and ECW in HD patients is unsatisfactory. The discrepancy between BIS and dilution techniques is related to the relative magnitude of body water compartments. Nevertheless, BIS adequately predicted acute changes in ECW during isolated ultrafiltration and HD, in contrast to changes in TBW.