Total body water measured by bioelectrical impedance in patients after hemodialysis. Comparison with urea kinetics.

Bioelectrical impedance (BEI) measurements have been used to measure total body water volume (VBEI). The VBEI were measured after hemodialysis in 14 patients, as was dialyzer blood water urea clearance (KBW) and dialysate urea clearance (KD). Urea clearance based on the mass transfer coefficient, KoA, was determined (KKoA). Residual renal function was measured, and three point variable volume single pool urea kinetic modeling (UKM) was done. Urea distribution volumes were calculated using the measured urea clearance values from blood water (VBW), dialysate (VD), and KoA (VKoA) as inputs. Direct dialysate quantitation was calculated based on total dialysate collections to measure urea clearance (KDDQ) and urea distribution volume (VDDQ). Total body water estimates were made using the Hume and Watson anthropometric formulas (VHUME and VWATSON). It was found that average VBEI (34.76 L) was larger than VBW (27.50 L) and VD (26.69 L), but it was not different from VKoA (32.15 L), VHUME (35.15 L), or VWATSON (34.53 L). Linear regression revealed a good correlation between VBEI and both VBW and VD (R = 0.873 and 0.882, respectively). The BEI measurements provide a simple method for measuring total body water in dialysis patients that correlated well with UKM volumes.