Assessment of degree of hydration in dialysis patients using whole body and calf bioimpedance analysis

Prescription of an appropriate post hemodialysis (HD) dialysis target weight requires accurate evaluation of the degree of hydration. The aim of this study was to investigate whether a state of normal hydration as defined by calf bioimpedance spectroscopy (cBIS) could be characterized in HD and normal subjects (NS). cBIS was performed in 62 NS (33 m/29 f) and 30 HD patients (16 m /14 f) pre-and post-dialysis to measure extracellular resistance. Normalized calf resistivity at 5 kHz (ρ_N,5) was defined as resistivity divided by body mass index. Measurements were made at baseline (BL) and at a state of normal hydration (NH) established following the progressive reduction of post-HD weight over successive dialysis treatments until the ρ_N,5 was in the range of NS. Blood pressures were measured pre-and post-HD treatment. ρ_N,5 in males and females differed significantly in NS (20.5±1.99 vs 21.7±2.6 10^-2 Ωm³/kg, p>0.05). In patients, ρ_N,5 notably increased and reached NH range due to progressive decrease in body weight, and systolic blood pressure (SBP) significantly decreased pre-and post-HD between BL and NBH respectively. This establishes the use of ρ_N,5 as a new comparator allowing the clinician to incrementally monitor the effect of removal of extracellular fluid from patients over a course of dialysis treatments.