Comparison of bioimpedance techniques to detect changes in fluid status in hemodialysis patients

Bioimpedance (BI) is maturing as a clinical technique for assessing fluid volume status. The aim of this study was to compare the sensitivity of four BI methods to detect changes in fluid status in hemodialysis patients.

Forty-five patients were studied twice in the same week, i.e. once after the long and short interdialytic intervals, respectively. The four BI methods used were: (a) calf normalized resistivity (CNR) at a 5-kHz frequency, (b) whole-body multifrequency BI spectroscopy (MF-BIS) to estimate the normal hydration weight (NHWWBM), (c) whole-body MF-BIS to estimate the ratio of extracellular volume to total body water (wECV/wTBW), and (d) whole-body single-frequency (50 kHz) BI analysis to compute the ratio of ECV (sfECV) to TBW (sfTBW).

The relationship (slope of the regressive line) between relative changes (%) in the above mentioned four BI parameters and differences in weight (kg) was most pronounced with CNR (5.2 ± 1.6%/kg), followed by wECV/wTBW (1.7 ± 0.7%/kg) and NHWWBM (0.73 ± 0.2%/kg). Changes in sfECV/sfTBW and differences in weight were not correlated.

CNR is more sensitive than whole-body BIS for detecting differences in fluid status.