• Clearance of solutes via diffusion down a concentration gradient
  • A counter-current flow of a solution containing various electrolytes on the opposite side of membrane to blood allows diffusion to occur
  • No fluid is added to the filtrate after diffusion
  • Rate of solute clearance determined by:
    • Concentration gradient between plasma and dialysate
    • Particle size, ionic charge and protein binding
    • Membrane pores, thickness and surface area
  • Clearance of solutes via convection driven by hydrostatic pressure
  • Filtrate removal is balanced by the addition of a solution to maintain volume
  • Does not significantly change the concentration of serum electrolytes and waste products unless a replacement fluid is infused into the blood, effectively diluting out those solutes the physician wishes to remove
  • Rate of filtrate and solute removal determined by:
    • Blood flow
    • Transmembrane pressure gradient
    • Membrane coefficient (pore size/permeability)
Haemodiafiltration (Combined)
  • Clearance of solute via convection and diffusion
  • Countercurrent dialysate is used in addition to hydrostatic pressure
  • Fluid replacement is required to maintain plasma volumes