Measurement of body composition changes during hemodialysis by bioimpedance analysis

Monitoring of fluid exchanges during hemodialysis is essential for the safety and efficacy of the procedure. Bioimpedance analysis has been used for the measurement of body compartments in many settings, but experience during hemodialysis is relatively scare. In a prospective study of 28 cases of chronic renal failure treated by long-term hemodialysis on an outpatient basis, body composition studies were done immediately before and after the dialysis session. Methods included body weight, serum albumin, hematocrit, hemoglobin, sodium and osmolality. These variables were compared with impedance (BIA) findings, namely lean body mass, body fat, total water, extra and intra-cellular water, third space, and exchangeable sodium/potassium ratio. Patients lost weight and improved hematocrit, hemoglobin, osmolality and serum sodium during the therapy, and BIA measurements were consistent with these changes. Lean body mass and body fat markedly changed along the dialysis session (respectively -24.5% and + 7.5%), and these results were out of proportion regarding known gains and losses in that period. It is concluded that BIA was useful for monitoring water fluxes during hemodialysis, but provided unreliable information about body fat and lean body mass.