Assessment of fluid distribution in patients on maintenance hemodialysis by bio-impedance spectrum analysis

Objective To evaluate the fluid distribution in patients on maintenance hemodialysis by the whole-body bio-impedance spectroscopy.Methods A total of 119 patients with stable hemodialysis for more than 3 months were enrolled in this study.Pre-and post-dialysis intracellular water(ICW) and extracellular water(ECW) were measured by whole-body multi-frequency bio-impedance spectroscopy(Bodystat,UK),and standardized by body weight to produce ICW% and ECW%.Eighty-two normal individuals of matched sex,age and body weight were used as controls.Results Patients on maintenance hemodialysis had significantly higher ECW% and ECW/ICW ratio compared with normal controls(P0.01).ECW% and ECW/ICW ratio decreased significantly after hemodialysis,but were still higher than those of controls.By contrast,pre-and post-dialysis ICW% values in HD patients were similar to those of controls.Lower ECW after dialysis was positively correlated with ultrafiltration volume(r=0.572,P0.01 for males;r=0.556,P0.01 for females).Patients with hypertension had higher pre-and post-dialysis ECW% values than those without hypertension.In patients with normal blood pressure,post-dialysis ECW% was similar to that of controls.Conclusions Hemodialysis patients have higher pre-dialysis ECW%.Fluid ultrafiltration is mainly derived from extracellular water during hemodialysis.Post-dialysis ECW% may be a useful parameter for the evaluation of dry weight in HD patients.