Before dialysis blood pressure and laboratory values ​​are checked.

Dialysis is an apparatus method for the treatment of certain diseases or symptoms in which the kidneys of the body do their job inadequately or not at all or in the patient no kidney is present.

In principle, in all the variants used, the entire blood of the patient is passed through a kind of filter, freed from pollutants and excess water and then returned to the body in a purified state - hence the popularly known synonym for dialysis: blood washing. It is therefore in most cases a renal replacement therapy due to a terminal renal insufficiency. The first modern-day dialysis of ill people was carried out in 1924 in Giessen. The technology became accessible to a broader mass from about 1945 and has since undergone a steady development with a growing number of application areas. Nowadays, dialysis is the major support in the treatment of renal replacement therapy, so that in 2010, there were approximately 70, 000 permanently dialysis-dependent patients in Germany, and the trend is rising.

Tasks of the kidney

The kidney, of which each human usually has two, is one of the most important organs of the body, without which man would not be viable. Not only does it regulate the water balance of the body via the urine excretion. In addition, it filters out harmful substances that the body can not degrade from the blood and is crucially involved in maintaining the electrolyte composition of the blood, ie the dissolved salts and ions. In addition, in the kidney hormones such as Epo ( erythropoietin ) are produced, which is important for blood production and most of whom are known from cycling, and regulates the pH. The pH value is a measure of the ratio of chemical acids and bases in the blood, which must be kept constant within narrow limits. Also in the adjustment of blood pressure, the kidney is crucially involved. This makes it clear which significance this organ and thus dialysis has as an important therapy option.


Access to the patient's blood is provided via catheters or shunts.

When using a dialytic therapy one must distinguish between acute complaints and chronic illnesses. In the field of acute events, dialysis is useful for the rapid recovery of vital functions. Areas of application here are above all the acute, sudden kidney failure or a high grade, not to be treated by medication overhydration as well as the acute poisoning. Dialysis, however, has the greatest relevance as the most important tool for kidney replacement therapy. This is always used when the kidneys themselves can no longer or no longer sufficiently perform the tasks assigned to them. This occurs on the one hand, when the kidneys are no longer available, for example as part of a tumor therapy in which both kidneys had to be removed. On the other hand, however, the vast majority of dialysis patients have chronic renal insufficiency, ie poor kidneys. In both cases, the above tasks are taken over by the dialysis machine. In rare cases, dialysis is also used in liver disease.


Generally, extracorporeal out-of-body dialysis will be distinguished from intracorporeal in-body dialysis. Most cases are extracorporeal treatments. Here, the patient is connected to the external dialysis machine, which then takes over the blood.

There are several technical principles to wash the blood. All methods have in common that first an access to the blood of the patient must be created. This is done via catheters (a type of thin tube) (acute) or dialysis shunts (chronic). The catheter commonly used in acute dialysis is the Shaldon catheter, which provides access to large peripheral veins on the neck or groin, allowing blood flow to and from the dialysis machine. If a patient is dependent on dialysis for a longer or lasting period of time, the establishment of a permanent access in the form of an arterio-venous shunt makes sense. Usually located on the forearm, one of the two forearm arteries is connected in a minor surgical procedure directly to the adjacent vein, so that in this vein arterial blood flows (so-called Cimino fistula). This type of shunt can be recognized by the fact that the vein is greatly enlarged at the affected area and so easy to poke. With bare hands you can also feel the blood flow in the shunt, sometimes you hear a noise.

Two sheds are then placed at this shunt: one sends blood to the dialysis machine, the other picks up the cleaned blood and brings it back to the body. The blood cleansing steps then take place in the attached dialysis machine. In addition, the modern dialysis machine has several filters that prevent, for example, the formation of gas bubbles in the blood, which can lead to complications. The administration of medication is also possible during dialysis via additional supply points. The heart of the device, which is usually about the size of a small dresser, is always a semi-permeable membrane. This means that a membrane is built in which has many microscopic pores and is therefore semipermeable: water, ions and smaller particles such as the unwanted pollutants can pass through the membrane. For larger particles dissolved in the blood, the pores are too small and they remain in the blood. These include, in particular, the blood cells (red, white blood cells and platelets) or vital proteins that you do not want to filter out.

On the membrane directly two mechanisms of importance, which are used to purify the blood and thus determine the possible variants of performing a dialysis: hemodialysis and hemofiltration (Greek: haima = blood). The basis of hemodialysis is the principle of osmosis. It describes the behavior of particles dissolved in water, in this case in blood, evenly distributed on a semipermeable membrane along concentration differences on both sides of the membrane. In order to take advantage of this effect in practice, one needs a specific solution for successful dialysis, the dialysate, which is located on one side of the membrane.

On the other hand, the patient's blood is derived from the other person. The composition of the dialysate is precisely tailored to the needs of the patient and thus allows a well-controlled exchange of substances between blood and dialysate along the membrane.

An example: If there is too much potassium in the patient's blood, dial a dialysate with a low potassium concentration, so that during dialysis the excess potassium ions travel through the membrane from the blood until a desired level is reached. It is possible in this way to regulate up or down all substances which can pass through the membrane. Excess water, which leads to edema, can be removed from the body in this way. In contrast, the hemofiltration is basically the same structure inside the device, but here is not a concentration difference responsible for the mass transfer. Instead, a slight negative pressure is generated on the semipermeable membrane by means of a pump, so that water and dissolved substances are continuously withdrawn.

In both methods, it is possible to optimize the result of dialysis by adding desired substances or liquid from the dialysis machine into the blood. A combination of both principles is also used in practice and is referred to as hemodiafiltration. So far, the typical principle of extracorporeal dialysis has been described. In the rare case of intracorporeal dialysis, a tube is implanted under the abdominal wall and flushed with solutions. Here, however, the body's peritoneum (peritoneum), which rests from the inside of the abdominal wall, serves as a membrane. One speaks of the Peritonealdialyse.


When a patient has insufficient renal function and is therefore dependent on dialysis is determined on the basis of the patient's clinical picture together with specific laboratory values. A good value associated with kidney function is creatinine. Nevertheless, increasing this value is not enough to definitely justify the beginning of dialysis. The more important and meaningful kidney value is the glomerular filtration rate (GFR). It is a measure of how well the kidneys can filter and thus cleanse the blood. The standard value of GFR for young adults is 100-120 ml / min.

In old age, this value naturally decreases steadily. However, from about 10-15 ml / min such a chronic kidney weakness is given that the permanent dialysis can not be avoided. In addition, acute events in the context of an emergency, such as acute renal failure or poisoning, are indications of dialysis. In the practical implementation of permanent dialysis, ie in classic dialysis patients, there are two options: outpatient dialysis or home dialysis. Ambulatory dialysis patients receive a dialysis plan at the beginning of the therapy, which firmly records the appointments of dialysis per week.

A popular and useful scheme would be, for example, the dialysis plan Monday-Wednesday-Friday. At least three times a week, the patient must go to a suitable place. Hospitals can perform dialysis on an outpatient basis, but in many places there are also dialysis centers specializing in the treatment of this group of patients. Here, the latest development is increasingly a nightly dialysis offered, in which the patient can sleep. The aim is to influence as little as possible the everyday life of those affected. A dialysis session lasts about 5-6 hours on average. Before each dialysis session, general parameters such as blood pressure, body weight and laboratory values ​​are recorded. Then the shunt is pierced with two cannulas and the blood is cleaned. The patients then return home.

A dialysis patient often notices significant fluctuations in mood between cycles. So it is the most people directly after dialysis significantly better than just before, because after 1-2 days again accumulated undesirable substances. The only way to get rid of the permanent dialysis duty is the kidney transplant. Without them, dialysis is a lifetime therapy. In acute or emergency dialysis, one or a few sessions are usually sufficient, as the kidney itself is still intact and only one poison or one cause had to be repaired.


Overall, dialysis is a safe and low-complication medical procedure. The most vulnerable component in dialysis therapy is the shunt. As with all invasive procedures, there is some underlying risk that an infection will spread, which in the worst case can become sepsis. However, this risk is extremely low. More often it happens that the shunt is closed by onset of coagulation: it forms in thrombus. In this case, surgical removal of the thrombus can be done by a surgeon. In the worst case, a new shunt must be set elsewhere. Many dialysis patients have other underlying conditions that can sometimes be secondary to problems. Thus, in oversaturated patients with limited cardiac function to ensure sufficient pumping power.

Because of the chronic kidney disease, it is especially important to control the amount of water drunk during the day. The rule of thumb for the amount of water to drink per day is urine residue excretion plus 500ml. In addition, nutrition also plays a significant role. Low-protein meals are recommended because the body converts many components of the proteins, the amino acids, into potentially toxic substances that kidneys can no longer excrete. Here, nitrogen plays a crucial role, from which the nerve cells damaging ammonia is produced. Even food that contains a lot of potassium - bananas, kale, wheat germ - should not or only in moderation. A constant potassium level in the blood is extremely important for normal heart work. For example, too high or too low potassium levels may be responsible for the spontaneous occurrence of defective heart actions.

Overall, dialysis is a low-impact and equally important measure that secures the lives of a large number of patients with end-stage renal disease worldwide or bridges the time to kidney transplantation without unduly restricting quality of life.

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