Assessing fluid change in hemodialysis: Whole body versus sum of segmental bioimpedance spectroscopy

Background. Accurate estimation of extracellular fluid (ECF) is an important factor in assessing dry weight in hemodialysis patients. Bioimpedance spectroscopy (BIS) is a simple method to determine the compartmental distribution of body water in HD patients. Recent studies have shown that sum of segmental BIS (SBIS) is less affected by the change of body position and may be more accurate in measuring ECF change than whole body BIS (WBIS). We have compared SBIS and WBIS in estimating change in fluid volume during hemodialysis. Methods. Twenty-eight patients (male 10, female 18) were studied during their regular hemodialysis. ECF changes estimated by both techniques were compared with actual weight change during the inter- and intradialytic periods. Results. Both techniques tracked fluid changes that correlated well with fluid loss during the dialysis run (WBIS, r = 0.75, P < 0.001; SBIS, r = 0.65, P < 0.001) and fluid gain in the interdialytic period (WBIS, r = 0.73, P < 0.01; SBIS, r = 0.6, P < 0.01). ECF changes estimated by SBIS and WBIS underestimated weight loss 0.78 +/- 0.01 L and 0.6 +/- 0.01 L, respectively; and underestimated weight gain 0.66 +/- 0.18 L and 0.76 +/- 0.18 L, respectively. Conclusions. While both WBIS and SBIS can be used to track relative ECF volume changes in HD patients, they are not accurate in quantifying changes in ECF volume. More studies are needed to evaluate the benefit of SBIS over WBIS in clinical practice.