Estimation of Body Hydration in Dialysis Patients Using a Calf Bioimpedance Method

Accurate estimation of normal hydration (dry weight) in hemodialysis (HD) patients is an important factor affecting patient mortality. Bioimpedance spectroscopy (BIS) has been used to measure extracellular (R
_e
) and intracellular resistance (R
_i
) with a calf method (cBIS). An algorithm based on a fluid dynamic (FD) model has been developed to estimate change in intradialytic fluid volume in the calf during HD. We hypothesize that the flattening curve of change in R
_e
and reaching the normal range of resistivity are the criteria to determine normal hydration state. The aim of this study was to evaluate whether the model and algorithm can be used in the clinic. 32 stable HD patients (19m/13f, age 55.8±15 yrs, height (H) 1.68±0.99 m and post-HD weight 71.9±15.3 kg) were studied with cBIS during HD treatments. To achieve dry weight, post HD weight were gradually reduced according to the criteria. Pre- and post-HD weight were reduced by mean of 1.36 kg and 1.15 kg respectively. The systolic blood pressure (SBP) decreased significantly (122.5± 22, vs. 114.3±21 mmHg, p<0.05). In conclusion, the FD model and algorithm has been applied successfully in dialysis patients.