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What is dialysis?

In the final stage of nephrotic syndrome (stage CKD G5), a human body is so poisoned/overhydrated that some people cannot breathe or their legs are so heavy due to the edema (overhydration) that dialysis, so-called blood washing, is carried out to detoxify/remove fluids must become.


Otherwise, a person has no chance of survival unless they have had a kidney transplant first.
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Dialysis procedure

There are several methods to rid the body of toxins and overhydration:


  • Hemodialysis HD

  • Peritonealdialysis PD

In hemodialysis, the filtration is carried out extracorporeally and, conversely, in peritoneal dialysis, the peritoneum’s own peritoneum takes over the filter function.


Here we explain the function of hemodialysis HD, which is also divided into hemofiltration HF, hemodiafiltration HDF and hemoperfusion HP in acute poisoning. Hemodialysis is the most commonly used procedure in Germany with most patients in so-called “renal replacement therapy”.


The dialysis machine

During hemodialysis, the blood is filtered using a dialysis machine (housing with measuring instruments, clamps, pumps and sensors, etc.), dialyzer (capillary filter element) with a tube system and the exchange solution (osmosis solution, electrolytes and bicarbonate, etc.).

In acute cases (or if this is not possible), the connection to the patient is achieved via a catheter on the carotid artery (Demers catheter, atrial catheter, etc.) or via the so-called shunt.

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The Shunt

Before dialysis (blood washing) takes place, a shunt (access, short-circuit connection) for HD dialysis must be created on the non-handled side of the forearm. This is usually done before the final stage with the shunt operation (surgery), as it requires maturation of up to 6 weeks.


The Shunt

The shunt (also called fistula) is created (shunt operation) in order to achieve the highest possible cleaning effect in a short time. This can be achieved with strong blood flow, which means wider vessels, which people with normal arm vessels do not have. (See picture “The Shunt”)


But remember: The kidneys carry out filtration and endocrine regulation continuously, but a dialysis patient is only allowed to undergo HD dialysis (Germany) 2x 4h to 3x 5.5h per week, depending on the progress of the disease. Nobody cares about endocrine regulation anyway, if any irregularities arise due to the 3-month blood collection rhythm. (Who makes these guidelines?). Nobody takes into account that the accompanying diseases flourish while waiting for a kidney transplant.


Dialysis needle – arterial and venous.

After “shunt maturation”, that is Expansion of the puncture vessels, will be every 2 days two needles (1.3 mm – 2 mm, which over time cause the puncture sites to mutate into wounds and aneurysms, which then also lead to stenosis) attached to these vessels (arterial and venous) and the blood then circulates on the machine’s hose system, driven by a Pump. This pumps the blood by rolling it on the specific location of the tube (elongated in a special shape/consistency). It presses the blood from the patient into the tube system past measuring sensors to the dialyzer. The total blood volume in this tubing system plus dialyzer is max. 300ml.


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The dialyzer (capillary)

The dialyzer element, also known as a “capillary” (densely arranged hollow fibers with a diameter of 190 μm – 300 μm), the most current ones consist of polypropylene PP (housing) and polyurethane PUR (filter elements), in the middle of the tube system is the actual filter element. These smallest dialyzer units have permeable (semipermeable) nanopores.
Dialyzer – capillary

The dialyzer, which is connected to the hose system (so-called extracorporeal blood circulation), also has two connections. A liquid called dialysate, similar to the electrolyte solution, flows through this.


The dialyzer uses the diffusion processes of the physical principle of osmosis:
Since there are two sides, the blood side and the electrolyte side, the “toxins” (urea, potassium, calcium, sodium and phosphates) are “filtered” with the effect of diffusion through the blood-impermeable semi-permeable pores of the capillary. The machine uses the fresh dialysis fluid for this.


The hemoglobin (red blood cells) are larger than the openings in the pores of the capillaries and therefore they cannot be flushed out to the electrolyte side. (See “dialyzer – capillary”)


semi-permeable membrane
semi-permeable membrane

Dialyzer, cut through
Dialyzer, average


The toxins (urinary substances + molecules that are smaller than the size of the capillary pores) only change sides: from the blood side to the electrolyte side and are essentially flushed out of the blood in the extracorporeal tube system with the used dialysis fluid.


Because this therapy only 4-5 hours is carried out every two days, collecting in the meantime Toxins (for dialysis patients, potassium, calcium, phosphate, etc. are toxins to an uncontrolled extent), urea and fluid in the human body (up to three liters of fluid and more on weekends if there is no self-restriction!).
The self-restriction consists of the following two points:
  1. ingestion
    Food restriction during dialysis
  2. Drinking quantity
    Drinking restriction during dialysis

Therefore, if a kidney transplant is no longer possible, it is desirable to aim for the longest possible duration of dialysis with a slow pumping speed and to obtain the best information/exchange in social networks about the long-term dialysis therapy.

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Chronic renal failure and dialysis


Explanatory graphics: Dialysis procedure Hemodialysis (HD)