Plasma volume changes induced by sequential ultrafiltration-hemodialysis and sequential hemodialysis-ultrafiltration.

Isolated ultrafiltration (UF) has been shown to preserve plasma volume (PV) by means of a high plasma refilling rate, mediated by a rapid rise in oncotic pressure. This mechanism contributes to the good tolerance of sequential ultrafiltration-hemodialysis (SUH). This study compared PV changes induced by SUH and sequential hemodialysis-ultrafiltration (SHU). Seven dialysis patients underwent two sets of SUH and SHU, in which 2 h of UF (approximately equal to 3L) respectively preceded or followed 2 h of no-weight-change hemodialysis (ISO HD). VEM (volume of extravascular mobilization), VEM/VUF (percent of plasma refilling rate) and delta PV were calculated by mathematical formulas. Results showed: 1) a high VEM/VUF during the UF period, either before or after ISO HD: 80 and 77% respectively; 2) a significant increase in PV during ISO HD after UF, compared to ISO HD before UF: + 229 ml and + 43 ml, P less than 0.05; 3) VEM/VUF significantly higher during SUH than during SHU: 87 and 80%, P less than 0.01. In conclusion, the decrease in PV was lower in SUH than in SHU (11 vs. 19%, P less than 0.001) because the plasma refilling persisted through the ISO HD period.