The term dialysis describes the process known as blood purification. The use of a dialysis procedure is primarily for patients with renal insufficiency, in whom the kidney is no longer able to filter and eliminate toxins and pollutants from the blood. Because of this, either a kidney transplant or dialysis therapy (extracorporeal renal replacement therapy) must be performed to cleanse the blood when kidney function is absent or severely reduced. In principle, kidney transplantation is the gold standard (therapy of choice) for severely suppressed and completely absent kidney function. However, in Germany there is a higher demand for donor kidneys than there are organ donors available, so that the majority of patients have to bridge the waiting phase until organ transplantation by means of dialysis. If a transplant is not possible due to various causes, dialysis therapy can be carried out for the patient’s entire life. Thus, next to kidney transplantation, dialysis is the most important renal replacement therapy for chronic kidney failure. Furthermore, however, there is the option of using dialysis as a treatment for acute kidney failure. Furthermore, it is possible to divide dialysis therapy into two subgroups. These are extracorporeal (outside the body) and intracorporeal (inside the body) or non-extracorporeal dialysis procedures. Of particular importance among the extracorporeal procedures is hemodialysis, which is the most frequently used dialysis procedure worldwide. Also included in the extracorporeal procedures are hemofiltration and hemodiafiltration. In addition, hemoperfusion and apheresis therapy are counted among the blood purification procedures, although it should be noted that the indication (indication for use) of these procedures is not chronic therapy for existing renal insufficiency, but the presence of other clinical pictures or poisoning. Thus, both hemoperfusion and apheresis therapy are not renal replacement therapy procedures. The following procedures are classified as dialysis therapy:
- Hemodialysis – to perform hemodialysis therapy, surgical implantation of a shunt is required. A shunt is an artificially created connection point between the arterial and venous blood. In principle, the procedure is performed exclusively on the upper or lower arm (usually at the wrist between the radial artery and the cephalic vein). The dialysis shunt should always be placed on the non-dominant arm, as the shunt arm must be protected in everyday life! Note: No blood pressure measurement, blood sampling and no placement of indwelling venous cannulae on the shunt arm!Depending on the patient’s constitution, complications can arise when placing the shunt, which can be reduced, for example, by using so-called vascular prostheses. The basic principle of hemodialysis is the creation of a concentration balance of precisely defined substances between two fluids separated by a semipermeable membrane. Substances are exchanged across this membrane according to the physical principle of osmosis. The two separated fluids are the patient’s blood, which contains all toxins and harmful substances, and the dialysate. The dialysate contains a buffer substance that can compensate for an imbalance in the pH value (acid-base balance). Furthermore, the dialysate is low in germs, electrolyte and contains no waste products.
- Hemofiltration – fundamental difference between hemofiltration and hemodialysis is the lack of use of a dialysate to carry out the therapeutic measure. Despite this difference, even when hemofiltration is used, a significantly better and therefore lower concentration of urinary and harmful substances is contained in the blood and therefore in the patient’s organism. Instead, hemofiltration involves fluid removal by ultrafiltration. This principle is based on the use of a hemofilter. This hemofilter used is characterized by the fact that it consists of a highly permeable membrane, which leads to the achievement of ultrafiltration rates in the range of 120 to 180 ml/min. By means of a pressure gradient applied to the filter membrane via a pump, plasma can be transported from the blood across the membrane, resulting in fluid removal.The consequence of this pressure gradient is still the removal of all filterable substances. It should be noted, however, that the removed liquid must be quickly replaced by an electrolyte solution. It should also be mentioned that hemofiltration is a mechanical process which can be divided into further subsystems. Spontaneous slow ultrafiltration (SCUF), continuous arteriovenous hemofiltration (CAVH), continuous arteriovenous hemofiltration with filtration pump and continuous veno-venous hemofiltration (CVVH) can be assigned to hemofiltration.
- Hemodiafiltration – this procedure is a combination of hemodialysis and hemofiltration, which is used exclusively for the therapy of chronic renal failure with therapeutic indication as a renal replacement procedure. Due to this combination of the two blood purification procedures, it is possible to perform the removal of both low and medium molecular weight substances. The removal of these substances can only be realized with a controlled replacement of the ultrafiltrate by physiological electrolyte solution. The replacement solution is added directly to the blood either before or after the dialyzer. In order to restore volume balance, it is necessary to remove the added fluid by dialyzer. Result of this process the generation of a higher transmembrane flow. As a result, the pollutants and toxins present in the blood can be eliminated more effectively.
- Peritoneal dialysis – this is a group of renal replacement procedures for the therapy of renal failure which have in common that for dialysis therapy a use of the peritoneum (peritoneum) as a filter membrane. For this purpose, a catheter system is implanted in the patient’s abdominal cavity either invasively (conventional surgery) or minimally invasively (with little damage to the abdominal skin). Following this procedure, a dialysis solution can be filled into the peritoneal space (abdominal cavity) via this catheter. The fate of the dialysate depends on the procedure used. However, the disadvantage of this procedure is that the peritoneum is protein permeable, so that a larger amount of protein is removed from the body.
- Home dialysis – both hemodialysis and peritoneal dialysis can be performed in the patient’s own home under certain conditions, such as the patient’s suitability for this therapeutic measure. By carrying out the therapy at home, more flexible time management can be achieved, which may result in the patient being able to continue working. In addition, it has been shown in various studies that the lethality (mortality related to the total number of people suffering from the disease) can be reduced by home dialysis.
Start of therapy
The IDEAL (Initiating Dialysis Early and Late) study investigated whether the statement: dialysis: the earlier the better holds true for patients with chronic renal failure (stage V)?In the early group, dialysis began at a GFR between 10 and 14 mlg/min/1. 73 and in the late group at a GFR between 5.0 and 7.0 ml/min/1.73.Result: overall mortality was the same for both groups!Conclusion: it is possible to wait until symptoms of uremia appear before starting dialysis.
