Background: It is the prevailing view that convective dialysis techniques stabilize blood pressure. The aim of this study was to compare the hemodynamics of high-dose predilution hemodiafiltration (HDF) and low-flux hemodialysis (HD), under matched conditions and using high calcium-ion concentration in the replacement/dialysis fluid.
Methods: 13 stable hemodialysis patients were investigated in a randomized crossover, blinded controlled trial. The patients were allocated to one session of predilution HDF (substitution fluid 1.20 1/kg BW) and one session of HD at 4.5 hours. At the start of the dialysis the patient's core temperature was "locked" by an automatic feedback system regulating the dialysate temperature, thereby patient's temperature was kept stable throughout the whole treatment. The Ca ion concentration in the substitution/dialysis fluid was 1.75 mM. Cardiac output was measured hourly by the ultrasound velocity dilution method.
Results: Within treatments comparisons revealed that both treatments displayed stable mean blood pressure and equally reduced cardiac output. HDF showed decreased stroke volume and increased total peripheral resistance. The pulse rate decreased significantly only during HD. Arterial temperature was kept constant during both treatments. Ultrafiltration volume, cardiopulmonary recirculation, relative blood volume, Kt/V and total energy transfer were matched for HD and HDF. The overall between treatments comparisons revealed no significant differences.
Conclusions: We have shown that during matched conditions and high calcium concentrations, the hemodynamic profiles of high dose predilution HDF and lowflux HD were similar. Both modalities showed stable mean blood pressure profiles. An acute circulatory benefit of convective solute removal over diffusive, could not be demonstrated.