A Device for Monitoring Hydration State in Hemodialysis Patients Using a Calf Bioimpedance Technique

We have developed a technique to monitor dry weight (DWM) using a segmental bioimpedance technique to continuously measure the change in resistance and resistivity (ρ) in the calf during hemodialysis (HD).The DWM was designed based on multifrequency bioimpedance spectroscopy (BIS) with frequencies from 1 to 300 kHz. An algorithm combines two parameters to determine DW, flattening of the curve of change in extracellular resistance (ΔRE0/REt<0.01) and normalized resistivity (μ = ρ /body mass index). 31 patients (12f/19m) were studied. Systolic blood pressure (SBP) and blood volume (BV) were measured. After three baseline (BL) measurements, post HD weight was gradually reduced every treatment. 21 patients reached DW criteria but 10 were still overhydrated (OH) due to lack of compliance. A significant decrease in post HD weight and increase in μ were observed in BL compared to DW (Wt 75.3±15 vs. 74.1±15 kg, p<0.001; μ 18.6±2.5 vs. 20.4±2, p<0.001) in OH (Wt 82.3±38 vs. 80.1±36 kg, p<0.05; μ 14.6±1.9 vs. 16.3±1.4, p<0.05). In patients at DW, the curves of ΔRE0/REt were flat and the μ was closer to normal range, while in OH patients neither the flattening curve nor normal μ were observed.