Estimation of peripheral blood volume and interstitial volume in hemodialysis patients using bioimpedance techniques

This paper describes a method to estimate interstitial fluid volume and peripheral blood volume (BV_P) in hemodialysis (HD) patients using whole body (wBIS) and calf (cBIS) bioimpedance spectroscopy techniques. The aim of this study was to evaluate the usefulness of the technique. Thirty five HD patients were studied pre and post HD. Extracellular volume (ECV) and total body water (TBW) were measured using wBIS and cBIS. The calf resistances at 5 kHz (R₅) and at 1000 kHz (R₁₀₀₀) respectively reflect ECV and TBW in the calf. A blood pressure cuff was placed over the area of cBIS. Regional and whole body plasma or BV_P and interstitial (V_IT) or total fluid volume are measured at R₅ or R₁₀₀₀ when the cuff was inflated to just above the systolic blood pressure. According to calf normalized resistivity (CNR) post HD, patients were divided into two groups: overhydration (OH, CNR<;18.5, 10^-2*Ωm³/kg) and normal hydration (NH, CNR≥18.5, 10^-2*Ωm³/kg). BV_P was higher in OH than in NH group which can be explained by the low ratio of change in V_IT to ultrafiltration volume in the OH group (0.57±0.23 vs 0.83±0.45 L, p<;0.05). In conclusion, the method could be useful to better understand fluid dynamics during HD.