Hemodialysis
Hemofiltration
Hemodiafiltration
Single-needle dialysis


Which Hemodialysis therapies are available?
A variety of methods are available for chronic hemodialysis: Conventional hemodialysis (HD), hemofiltration (HF) and hemodiafiltration (HDF). Another possible therapy is the single-needle dialysis, in which case only one cannula or a single-lumen catheter is used to access the blood.
 
How does Hemodialysis work?

• Hemodialysis
  As the most widely used blood purification method, hemodialysis serves as a replacement for renal detoxification and discharge functions in the event of chronic kidney failure. The patient's blood is routed via a vessel access point by means of a blood pump through a bloodline system into the dialyser (artificial kidney). This is where the blood is cleaned. The blood flows through the dialyser's capillaries, while the dialyser liquid is bypassed outside the capillary walls in the direction opposing the flow of blood. The capillary walls are semi-permeable, i.e. they permit an exchange of substances between the blood and dialyser liquid. The primary transport mechanism during hemodialysis is selective diffusion. The size of the semi-permeable capillary walls' pores determines which molecules are able to diffuse from the blood into the dialyser liquid and vice versa. The capillary walls can be permeated by small and medium-sized molecules and water, but not by blood cells or large molecules, e.g. proteins. This eliminates toxic substances, restores normal concentrations of other substances (e.g. electrolytes such as potassium, sodium and calcium), balances the blood pH value and removes excess water which has accumulated in the body.
  While individual substances are eliminated mainly by diffusion, the water is filtered by the capillary walls' semi-permeable membrane out of the blood and into the dialyser liquid (ultrafiltration). This is made possible by the positive pressure on the blood's side and the negative pressure on the dialyser liquid's side (trans-membrane pressure, TMP).
• Hemofiltration
  Hemofiltration (HF) differs from hemodialysis in that no dialyser liquid is routed through the dialyser; instead a hemofiltration solution is infused directly into the blood and removed again in the hemofilter via ultrafiltration. In this process, the ultrafiltered water also rids the blood of the substances requiring discharge via urine. The advantage of this convective transport of substances is its ability to also remove larger molecules (medium-sized ones such as ß2 microglobulin), which cannot be eliminated as effectively by means of conventional hemodialysis.
• Hemodiafiltration
  A combination of hemodialysis and hemofiltration, i. e. hemodiafiltration (HDF), incorporates the advantages of both these therapies. Low-molecular substances are removed primarily by diffusion, medium-molecular substances by convection. A simultaneous application of hemodialysis and hemofiltration allows low-molecular and medium-molecular substances to be eliminated in a total proportion higher than that achieved by just one of the two therapies alone.
• Single-needle dialysis
  Single-needle dialysis is a therapeutic option used especially in cases where blood removal and return are only possible via one cannula or a single-lumen, central venous catheter. This constitutes a special technique, because one and the same cannula must be used to remove the blood and feed it back after cleaning in the dialyser. This kind of system always operates in two phases. During the arterial phase, the patient's blood is removed and pumped through the dialyser. During the venous phase, the purified blood is supplied back to the patient. A variety of single-needle systems with one or two blood pumps are available. The main disadvantage of most such systems is the constant interruption to the flow of blood through the dialyser.

The single-needle crossover system contains two blood pumps which run continuously without any interruptions. Compared with a conventional, single-needle system, the single-needle crossover system ensures a continuous flow of blood and a relatively constant pressure in the dialyser. This increases the dialysis efficiency.