Importance of the plasma refilling rate in the genesis of hypovolaemic hypotension during regular dialysis and controlled sequential ultrafiltration-haemodialysis.

The effects of ultrafiltration (UF) on plasma volume (PV) have been studied in eight patients using regular dialysis (RD) and controlled sequential ultrafiltration-haemodialysis (CSU) performed with a Rhodial 75 dialysis system. For a given value of UF the reduction of PV is determined by the plasma refilling rate. During CSU ultrafiltration induces a rapid increase in oncotic pressure without decreasing plasma osmolality. The high plasma refilling rate which can reach 1500 ml/hr allows moderate hypovolaemia despite high rates of UF and contributes to the usual good clinical tolerance of CSU. During RD a rapid decrease in plasma osmolality contributes to a water shift from the vascular space towards the interstitial and intracellular spaces and severe hypovolaemia can occur despite moderate ultrafiltration. CSU offers an adequate treatment for sodium overloaded patients with hypervolaemia, but is of no benefit in routine conditions.