Evaluation of Dry Weight in Dialysis Patients Using Bioelectrical Impedance Analysis (BIA)

Background: It is essential to define dry weight (DW) for each patient in clinical dialysis. The evaluation of DW by clinical observations of body weight (BW) changes, congestion, oedema, blood pressure and pulmonary X-ray is not very accurate. Bioimpedance could be more accurate in measuring the composition of different body fluid compartments. The present study was conducted to investigate the change of TBW, ECF, ICF by BIA between dialysis patients (including HD and CAPD) and normal control. Methods: Thirsty five dialysis patients (HD 21 patients and CAPD 14 patients) and forty sex and age matched control have underwent BIA measurement. The dry weight of dialysis patients were clinically determined by nephrologists through conventional methods such as physical examination of fluid status, blood pressure and C/T ratio. BIA was performed with a multifrequency bioimpedance analyzer (Biospace, USA) Both pre- and post-hemodialysis measurement were performed. Among the hemodialysis patients, edematous and nonedematous group were divided based on ECF/TBW ratio greater or less than 0.35. Results: There were no difference of TBW/BW ratio neither among dialysis groups and normal control groups nor between pre- and post-hemodialysis period. Eventhough there were no difference of ECF/TBW Between HD group and CAPD group, there were significant difference between dialysis groups and control group (HD 0.35±0.013 vs control 0.328±0.010, p＜0.01; CAPD 0.343±0.010 vs control 0.328±0.001, p＜0.01). There were significant difference of ECF/TBW ratio between edematous group and normal control, but no difference between non-edematous group and normal control. Interestingly, there were no significant relationships between TBW/BW and ECF/TBW. The ICF/ECF ratio showed significant difference either at pre- or post-hemodialysis period. The percentage of change of ECF were greater than that in ICF either at pre- or post-hemodialysis. One the other hand, the ECF/TBW ratio while not TBW/BW ratio correlated with C/T in dialysis patients. By the way, evidence that ultrafiltration fluid during hemodialysis are much more from ECF and interdialysis weight gain are distributed more to ECF than ICF might elucidate that ECF/TBW is more accurate evaluation of dry weight than TBW/BW. Conclusions: Our data suggested that ECF/TBW ratio was more accurate than TBW/BW ratio to evaluate the dry weight in dialysis patient. ECF/TBW ratio determined by BIA method is an useful clinical tool determining dry weight.