A method for the estimation of hydration state during hemodialysis using a calf bioimpedance technique

Although many methods have been utilized to measure degrees of body hydration, and in particular to estimate normal hydration states ( dry weight, DW) in hemodialysis (HD) patients, no accuratemethods are currently available for clinical use. Biochemcial measurements are not sufficiently precise and vena cava diameter estimation is impractical. Several bioimpedance methods have been suggested to provide information to estimate clinical hydration and nutritional status, such as phase angle measurement and ratio of body fluid compartment volumes to body weight. In this study, we present a calf bioimpedance spectroscopy (cBIS) technique to monitor calf resistance and resistivity continuously during HD. Attainment of DW is defined by two criteria: ( 1) the primary criterion is flattening of the change in the resistance curve during dialysis so that at DW little further change is observed and ( 2) normalized resistivity is in the range of observation of healthy subjects. Twenty maintenance HD patients ( 12 M/8 F) were studied on 220 occasions. After three baseline (BL) measurements, with patients at their DW prescribed on clinical grounds ( DWClin), the target post-dialysis weight was gradually decreased in the course of several treatments until the two dry weight criteria outlined above were met (DWcBIS). Post-dialysis weight was reduced from 78.3 +/- 28 to 77.1 +/- 27 kg ( p < 0.01), normalized resistivity increased from 17.9 +/- 3 to 19.1 +/- 2.3 x 10(-2) Omega m(3) kg(-1) (p< 0.01). The average coefficient of variation ( CV) in three repeat measurements of DWcBIS was 0.3 +/- 0.2%. The results indicate that cBIS utilizing a dynamic technique continuously during dialysis is an accurate and precise approach to specific end points for the estimation of body hydration status. Since no current techniques have been developed to detect DW as precisely, it is suggested as a standard to be evaluated clinically.