Adjusting Dry Weight by Extracellular Volume and Body Composition in Hemodialysis Patients

Abstract

Background: At present, the determination of dry weight in patients on hemodialysis is largely made empirically by trial and error. Extracellular volume (ECV) assessment by bioimpedance analysis (BIA) is a preferable technique for determining dry weight, and it also provides useful data on body composition. Methods: We measured the ECV of 74 normal subjects and 121 stable chronic hemodialysis patients postdialysis. In addition, for the dialysis patients, we measured intracellular volume (ICV) and lean body mass (LBM) by BIA, and analyzed the ECV, blood pressure and complications of dialysis. We adjusted dry weight according to the ECV and repeated a BIA exam 4 months later to evaluate changes in body composition, blood pressure and dialysis status of these patients. Results: The ECV as a percentage of weight (ECV%) of hypertensive patients was significantly higher than that of normotensive patients (24.29 ± 3.56% vs. 21.50 ± 2.38%, p < 0.001). All patients with excessive ECV% had hypertension, but not all hypertensive patients had excessive ECV%. None of the normotensive patients had ECV excess. Some hypertensive patients with symptoms of dialysis complications still had excessive ECV%. Eight hypertensive patients with excessive ECV had decreased dry weight. ECV% (29.80 ± 2.03% vs. 27.10 ± 2.99%, p < 0.001) and blood pressure (159 ± 7 / 97 ± 4 vs. 137 ± 10 / 86 ± 8 mm Hg, p = 0.006 for systolic and p = 0.004 for diastolic) decreased. ECV was the only portion of body composition that decreased (p < 0.001) after decreasing dry weight, the other parameters remaining unchanged. Twenty symptomatic normotensive patients improved with elevation of the dry weight. The ECV (p = 0.007), ICV (p = 0.009) and LBM (p < 0.001) were significantly increased after increasing dry weight, while the ECV% (p = 0.39) and fat (p = 0.46) remained unchanged. Conclusions: (1) For hypertensive patients, ECV must be evaluated in order to adjust dry weight and correct hypertension. (2) For normotensive patients, if dialysis complications occur, dry weight should be increased until symptoms disappear or the blood pressure begins to rise.