Effect of ultrafiltration on peripheral urea sequestration in haemodialysis patients

Background. Ultrafiltration (UF) is assumed to enhance urea removal during haemodialysis (HD) because of convective transport and because of contraction of urea distribution volume. However, UF‐induced blood volume reduction has been hypothesized to enhance peripheral urea sequestration and post‐dialysis urea rebound (PDUR), possibly reducing HD effectiveness. The effect of UF on PDUR was investigated in this study. Methods. Nine HD patients were studied on two subsequent treatment days. The first HD was performed with UF (UF‐rate=0.78±0.27 l/h), and the second treatment without UF. Serial measurements of serum water urea nitrogen concentration, arterial blood pressures (BP), and relative blood volume changes (ΔBV%) were obtained over the duration of HD. Results. BP and ΔBV% decreased with UF (BPsys= −9%, BPdia=−8%, BPmean=−9%, ΔBV%=−15%) but increased or remained unchanged without UF (BPsys= 9%, BPdia=12%, BPmean=11%, ΔBV%=1%). PDUR was 28.6±9.6% without UF, and increased in every single patient with UF (40.7±13.2%, P