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 contracti on of urea distribution volume. However, UF-induced blood volume reduction has been hypothesized to enhance peripheral urea sequestration and post-dia lysis urea rebound (PDUR), possibly reducing HD effectiveness. The effect o f UF on PDUR was investigated in this study. Methods. Nine HD patients were studied on two subsequent treatment days. Th e first HD was performed with UF (UF-rate = 0.78 +/- 0.27 l/h), and the sec ond treatment without UF. Serial measurements of serum water urea nitrogen concentration, arterial blood pressures (BP), and relative bland volume cha nges (Delta BV%) were obtained over the duration of HD. Results, BP and Delta BV% decreased with UF (BPsys = -9%, BPdia = -8%, BPme an= -9%, Delta BV% =-15%) but increased or remained unchanged without UF (B Psys = 9%, BPdia = 12%. BPmean = 11%, Delta BV% = 1%). PDR was 28.6 +/- 9.6 % without UF, and increased in every single patient with UF (40.7 +/- 13.2% , P < 0.01). Modelled perfusion of the peripheral low-flow compartment decr eased from 1.45 <plus/minus> 0.54 l/min without UF to 0.91 +/- 42 l/min wit h UF (P < 0.05), thereby explaining an enhanced two-compartment effect and increasing PDUR. Conclusion. The significant increase in the two-compartment effect of urea kinetics observed in current HD accompanied by UF call be explained by comp ensatory, intradialytic blood flow redistribution induced by blood volume r eduction. Because of the link between UF and blood flow. limited salute cle arance treatment modes that optimize fluid removal such as variable UF will also have favourable effects on delivered dose of dialysis.