Role of bioimpedance spectroscopy in assessment of body water compartmentsin hemodialysis patients

Bioimpedance spectroscopy (BIS) has been advocated as a tool to assess flui d 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) an d extracellular volume (ECW) measured by BIS and tracer dilution (deuterium oxide [D2O] and sodium bromide [NaBr]), the influence of the relative magn itude of water compartments (expressed as TBW2DO and ECWNaBr:body weight) o n the agreement between BIS and tracer dilution, and the ability of BIS to predict acute changes in fluid status. BIS and tracer dilution techniques w ere performed in 17 HD patients before a dialysis session. Moreover, the re lation between BIS and gravimetric weight changes was assessed during both isolated ultrafiltration and HID. Correlation coefficients between TBW and ECW measured by BIS and tracer dilution were r = 0.71 and r = 0.71, respect ively. Mean differences (tracer-BIS) were 6.9 L(limits of agreement, -1.5 t o 21.6 L) for TBW and 2.3 L (limits of agreement, -1.7 to 9.7 L) for ECW. T here was a significant relationship between the relative magnitude of TBW a nd 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, t here was a significant relation between gravimetric changes and change in E CWBIS (r = 0.83 and r = 0.76; P < 0.05), but not with change in TBWBIS. In conclusion, agreement between BIS and tracer dilution techniques in the ass essment of TBW and ECW in HD patients is unsatisfactory. The discrepancy be tween BIS and dilution techniques is related to the relative magnitude of b ody water compartments. Nevertheless, BIS adequately predicted acute change s in ECW during isolated ultrafiltration and HD, in contrast to changes in TBW. <(c)> 2001 by the National Kidney Foundation, Inc.