Assessment of excess fluid distribution in chronic hemodialysis patients using bioimpedance spectroscopy

Sodium and water homeostasis is abnormal in hemodialysis (HD) patients, however, the distribution of the excess fluid (extracellular vs. intracellular) has not been fully characterized. We studied the distribution of fluid using bioimpedance spectroscopy to determine if HD patients have an excess of fluid in any specific compartment relative to controls. Dual-energy x-ray absorptiometry was used to measure lean body mass and bone mineral content. The resistive index (RI) for extracellular water volume (RIECW), was significantly increased in patients pre-HD when corrected for bone mineral content (RIECW:BMC) (pre-HD, 19.0 +/- 3.3; controls, 15.8 +/- 1.7 cm2-ohms(-1)-kg -1; P < 0.01). This value decreased to the control range following HD (15.2 +/- 2.5 cm2-ohms(-1)-kg(-1). The intracellular water volume to bone mineral content (RIICW:BMC) was not different between controls and HD patients. These data suggest that hemodialysis patients carry their excess fluid volume primarily in the extracellular compartment and that bioimpedance spectroscopy coupled with a stable measure of lean tissue such as bone mineral content can determine the degree of relative excess hydration.