Principles of Haemodiafiltration: Rationale for Improved Patients’ Survival

Haemodiafiltration (HDF) is a renal replacement modality that combines diffusion and enhanced convection in order to remove small- and middle-molecular-weight compounds, respectively. They are removed along solvent drag effect of ultrafiltration through increased transmembrane pressure (TMP), whereas the replacement solution is infused intravenously at equal amount minus the desired fluid volume removal for achieving dry weight. Limiting factors for high-volume on-line haemodiafiltration (HV oHDF) are blood flow and viscosity (haematocrit, protocrit), filter performance and technical features of HDF monitor. Most recent advanced technology of dynamic analysis of pressure pulses along the blood flow pathway in the dialyser has enabled optimal ultrafiltration flow performances. HV oHDF offers today the best compromise of cardioprotective option by reducing cardiovascular risk factors in end-stage kidney disease patients. Recent randomised controlled trials (RCTs), individual participant data meta-analyses and a number of observational studies have shown the evidence of survival advantage of HDF over conventional haemodialysis (HD). The convective volume has become the key quantifier for HV oHDF as the measure of dialysis dose. Its cut-off values for better survival have been recognised, but the research is still needed in the years to come to set the required optimal volumes tailored to individual patients’ needs.