The kidneys are essential organs for our body, as through the filtering activity they purify the blood from the excess liquid component and toxins; moreover, they also carry out a regulatory activity, through which the correct hydro-saline and acid-base balances in the blood are maintained.

When these two fundamental organs can no longer fully perform the filtering function, a treatment is used to reproduce it artificially. This therapy is called DIALYSIS, and is prescribed by a doctor when a disabling nephrological pathology is diagnosed, such as chronic renal failure; that is, a disease that progressively affects kidney function, to the point of irreversibly compromising it, to the point of considering, in certain cases, transplantation, when possible.

Dialysis respects the principles of passive diffusion of solutes and ultrafiltration of fluids, allowing us to keep our body in balance: removing catabolites, salt and fluid overload, in order to avoid a harmful accumulation in the blood. At the same time, it keeps the levels of certain substances stable, such as sodium, potassium and bicarbonate, whose imbalance can be potentially dangerous, and finally helps to keep blood pressure under control. In essence, dialysis replaces the natural function of the kidneys.


There are 2 dialysis techniques:


How does dialysis eliminate waste and toxins in the body: the passive diffusion of solutes

This procedure is performed in the hospital or in specialized outpatient centers, and consists in the purification of blood through a dialyzer, that is, a plastic cylinder that performs the functions of an artificial kidney, and is formed by a filter that inside it has numerous hollow fibers with microscopic pores.

The aforementioned fibers are connected to both ends of the cylinder, forming a real compartment, and above all a semipermeable synthetic membrane.

Inside the hollow fibers the blood is flowed, sent to the machine by an arterial catheter, while outside them, the dialysis fluid is flowed. The levels of the latter are established by a nephrologist and are obviously different, depending on the needs of the patient, so as to favor the transfer of particular molecules in the required direction. Inserisci  Traduzioni di molecules sostantivo

In fact, every minute, about 300 ml of blood and 600 ml of fluid, with different concentrations, flow in the opposite direction, in the dialyzer, allowing the correct exchange of solutes.

The membrane, being semipermeable, allows the passage of molecules, based on their electrochemical gradient (passive diffusion), preventing instead that of the corpuscular elements of blood and proteins.

At the end of the purification, the blood leaves the device from one end, returning to the patient via the venous catheter. While the dialysis solution, containing the toxic substances and excess fluids removed from the blood, evidently comes out from the other end.

How dialysis eliminates excess body water: fluid ultrafiltration

In hemodialysis, if the external pressure of the hollow fiber is lower than the internal one, then excess body fluid is eliminated, at the moment when it flows inside the hollow fiber.

Most patients require three sessions a week, four hours each.

An important role in haemodiafiltration is played by the convention, i.e. a different process to carry out hemodialysis.

This procedure, considered particularly effective, involves the water being pushed through the membrane, thanks to the hydrostatic pressure. Together with liquids, the pressure is also able to move toxins and waste molecules, through the semipermeable membrane, thus providing a result of considerable impact.


Peritoneal dialysis is a process of blood purification that consists, in the exploitation of a natural semipermeable dialysis membrane, which is already present within our body, that is, the peritoneum, in the same way that the semipermeable membrane is used in hemodialysis.

The peritoneum envelops and supports numerous abdominal organs, such as the liver and stomach, and is formed by blood vessels, which make it suitable for filtration, just like the kidneys.

Through a catheter, which is inserted into the peritoneal cavity, the dialysis fluid is introduced, allowing the exchange of solutes between the blood flowing inside the capillaries of the peritoneum and the fluid. After a period of time of about 4-6 hours you can remove the fluid from the abdominal cavity.

How dialysis removes excess body water: osmosis

In order to remove excess body water, glucose is added to the dialysis fluid. Considering the fact that glucose molecules cannot easily pass through the peritoneum membrane, water is able to move thanks to the peritoneum in the dialysis fluid, to balance the difference in fluid concentration. In summary, fresh dialysis fluid is introduced continuously, and excess water is eliminated through the blood, thus avoiding an accumulation of water in it.

This procedure is performed in hospitals but can also be carried out at home, with the appropriate precautions, and two distinct methods:

manual peritoneal dialysis,performed by the patient or by specialists of the center, with a change of fluid about 4/5 times in 24 hours

automated peritoneal dialysis, an automated device is used to carry out the replacement of fluid several times during the night, while the patient sleeps

Most often, the choice of what kind of dialysis to adopt strongly depends on the patient and his health condition, because both solutions (hemodialysis and peritoneal dialysis) guarantee equivalent results. This means that an assessment must be made based on the benefits, preferences and habits of the patient and any problems of these procedures.

As a first form of treatment, peritoneal dialysis is strongly recommended, especially for children aged three and over and for adults who suffer from kidney disease, but do not have other pathologies or serious health conditions.

Hemodialysis is a procedure used mainly by older people, or in any case by those who do not enjoy a good state of health.


The possible side effects of dialysis are varied:

Anemia, typical of those who have dietary restrictions or have loss of iron and vitamins and those suffering from chronic renal failure due to poor production of erythropoietin, a hormone that stimulates the generation of red blood cells

Weakening of the bones, due to the non-production of vitamin D due to renal malfunction, thereby creating disorders of calcium metabolism.

Hypotension, that is, the lowering of blood pressure, which occurs especially in diabetic patients, due to the decrease in fluids.

Muscle cramps, also due to the scarcity of fluids and can be relieved with the regulation of fluids and sodium


Hyperkalemia, that is, having very high potassium levels

Amyloidosis, caused by the accumulation of blood protein material, on tendons and joints

Staph infections, especially for patients undergoing hemodialysis who are continuously exposed to bacteria that can cause serious infections; these there is a possibility that they spread in the blood, up to cause sepsis, that is, a multiple organ dysfunction

Peritonitis, frequent especially when it comes to peritoneal dialysis and consists of bacterial infection of the peritoneum

Weight gain


We can say, in conclusion, that dialysis is a very demanding procedure and that a strong spirit of collaboration is needed on the part of the patient, but it is rightly counted among the life-saving therapies. However, it does not allow you to go to fully recover the kidney function, in fact it can only partially compensate for this lack and is not considered a definitive cure. In fact, many people continue with this therapy for a very long time, in some cases even for life; while, for a minority of patients the therapy is carried out until the kidney transplant takes place, then after finding a compatible donor.