Non-euvolaemia in HD patients is associated with elevated mortality risk. Achievement of a normal hydration state is one of the major targets of hemodialysis (HD) therapy. An abnormal hydration state has been associated with arterial hypertension, dialysis associated hypotension and other symptoms and signs include pulmonary and peripheral edema, heart failure, left ventricular hypertrophy and other adverse cardiovascular events. To determine the hydration state clinical surrogate parameters are used such as interdialytic weight gain, ultrafiltration rate or blood pressure. Several authors have reported an important improvement in cardiac conditions by volume optimal monitoring strategy in HD patients. Charra and Chazot (1) and Ozkahya et al. (2) studies have shown that a strict volume control strategy decreases blood pressure (BP) without drugs, causes regression of LVH, and prolongs survival. Kalantar-Zadeh et al. examined 2-year mortality in 34,107 hemodialysis patients across the United States who had an average weight gain of at least 0.5 kg above their end-dialysis dry weight by the time the subsequent hemodialysis treatment started. They concluded, that, the greater fluid retention between 2 subsequent hemodialysis treatment sessions is associated with higher risk of all-cause and cardiovascular death (3).

Bioimpedance technology is based on passing a bioelectrical current through the body, and it estimates the body fluid volume by the amount of resistance this current endures in the body tissues. The bioelectrical current used in these devices can have segmental, spectral, or multi-bioelectrical frequencies. At present time, available bioimpedance techniques are generally classified using different frequency spectrum: the first option is the single frequency at 50 kHz or other current frequency bioimpedance (BI) analysis (SF-BIA), the multifrequency BI analysis using more than one frequency (e.g., 5, 50, and 100 kHz) and finally multifrequency BI spectroscopy (MF-BIS) using a range of frequencies such as 5 kHz to 1000 kHz to measure extracellular and intracellular resistance by Cole model. Two options for practical measurement of hydration status is based on whole body (wrist to ankle) measurements, or segmental (arm, trunk, and leg) measurements including calf BI spectroscopy (4, 5). The widely useful BIS technique, especially in European dialysis units is the body composition monitor (BCM) is based on a whole-body BI model, which is established with ECV, ICV, and body weight based on parameters from regression analysis in HSs to calculate fluid overload (FO) in dialysis patients. Webel et al. reported usefulness of the model in a clinical study with BCM guiding the reduction of FO in five hundred HD patients to achieve normal blood pressure (6). Raimann et al. compared the study of 49 HD patients of a single and multifrequency-BIA to direct estimation methods using isotope technique of TBW, ECF, and ICF in 49 hemodialysis patients. Comparisons of indirect methods (IEMs) to DEMs showed no significant differences and proportional errors (7).