Changes in Intracellular Water Following Hemodialysis Treatment Lead to Changes in Estimates of Lean Tissue Using Bioimpedance Spectroscopy

Abstract

Background: Bioelectrical impedance (BIA) devices are being introduced into hemodialysis (HD) centers to aid determining normohydrated weight and also provide body composition assessment by estimating lean tissue mass index (LTMI) and fat mass index (FMI). BIA devices differ, with most using a 2-body compartmental model, which can be affected by hydration status, and as such for reliable measurements, these should be made postdialysis when patients are not overhydrated, which is inconvenient for both patients and staff. The development of BIA devices using a 3-compartmental body model, separately estimating normohydrated LTMI potentially, now offers the advantage of making reliable measurements of body composition prior to dialysis.

Materials and methods: We measured body composition predialysis and postdialysis in 50 HD patients using a 3-body compartment model BIA device.

Results: Although there were no statistically significant differences for the whole cohort in LTMI and FMI (pre and post HD-13.5 ± 4.2 vs 13.9 ± 4.7 kg/m(2), and 10.5 ± 5.5 vs 10.6 ± 5.4 kg/m(2) respectively), the correlation (r(2)) between pre and post HD was only 0.27 and 0.37 kg/m(2) respectively, with a mean ± SD bias on Bland-Altman analysis, -0.67 ± 4.25 and 0.33 ± 4.77 kg/m(2) respectively. Changes in intracellular water were associated with changes in LTMI (r(2) = 0.99, P < .001). Similarly, a fall in LTMI was associated with a corresponding increase in FMI (r(2) = -0.86, P < .001).

Conclusion: In clinical practice, predialysis bioimpedance measurements are more convenient. However, for more reliable and reproducible assessments of nutrition status, we suggest that measurements of body composition should be made when patients are not overhydrated.

Keywords: bioimpedance; body composition; extracellular water; fat mass; hemodialysis; intracellular water; muscle mass.