Comparative Impact of Isolated Ultrafiltration and Hemodialysis on Fluid Distribution: A Bioimpedance Study

Abstract

Introduction: Isolated ultrafiltration (IUF) is an alternative treatment for diuretic-resistant patients with fluid retention. Although hemodialysis (HD) predominantly decreases extracellular water (ECW), the impact of IUF on fluid distribution compared with HD remains unclear. Methods: We compared the effect of HD (n = 22) and IUF (n = 10) sessions on the body fluid status using a bioimpedance analysis device (InBody S10). Results: The total ultrafiltration volume was similar between HD and IUF (HD 2.5 ± 0.3 vs. ICF 2.1 ± 0.3 L/session, p = 0.196). The reduction rate of ECW was significantly higher than that of intracellular water (ICW) after HD (ECW −7.9% ± 0.8% vs. ICW −3.0% ± 0.9%, p < 0.001) and IUF (ECW −5.8% ± 0.9% vs. ICW -3.6% ± 0.8%, p = 0.048). However, the change in the ratio of ECW to total body water in HD was significantly larger than that in IUF (HD −3.2% ± 0.3% vs. ICF −1.1% ± 0.4%, p < 0.001). The reduction rates in serum tonicity (effective osmolality) were higher after HD than after IUF (HD −1.8% ± 0.5% vs. IUF −0.6% ± 0.2%, p = 0.052). Among the components of effective osmolality, the reduction rates of serum K⁺ and glucose levels after HD were significantly higher than those after IUF (serum K⁺: HD −30.5% ± 1.6% vs. IUF −0.5% ± 3.8%, p < 0.001; serum glucose: HD −15.4% ± 5.0% vs. IUF 0.7% ± 4.8%, p = 0.026), while the serum Na⁺ level was slightly and similarly reduced (HD −0.8% ± 0.4% vs. IUF −0.8% ± 0.4%, p = 0.500). The reduction in the osmolal gap value (measured osmolality–calculated osmolarity) was significantly greater after HD sessions than after IUF sessions (HD −12.4 ± 1.4 vs. IUF 2.0 ± 1.0 mOsm/kg, p = 0.001). Conclusion: The extracellular fluid reduction effect of HD is stronger than that of IUF. The different changes in effective osmolality and osmolal gap after HD and IUF sessions may be related to the different effects of HD and IUF on fluid distribution.