Dialysis is a process that is generally used to remove excess salts and water from the intravascular space. The method is mainly used as replacement therapy for non-functioning or damaged kidneys as a result of acute or chronic renal failure.
There are two main methods of dialysis – hemodialysis and peritoneal dialysis, each of which has its advantages and disadvantages. The choice of one of the two methods depends both on the experience of the attending physician/dialysis center and on the child himself, his clinical condition, the presence of contraindications, etc.
Hemodialysis
The main principles by which hemodialysis works are diffusion of salts and ultrafiltration of water through semipermeable membranes. This means that the blood must flow on one side of the dialysis (semi-permeable) membrane, and the dialysis fluid flows on the other side, i.e. between the two, an exchange of water and salts dissolved in it takes place through the semipermeable membrane.
The exchange takes place due to the different concentration gradient between the two liquids, resulting from the different content of salts in them. Only the substances that are in the vascular space, i.e. the blood, are subject to hemodialysis. For example, if there is a syndrome of impaired capillary permeability with deposition of fluids in the extravascular space, it is first necessary to “enter” this extravascular fluid back into the vessels, and then it is subject to “purification” by hemodialysis.
In hemodialysis, the semi-permeable membrane is “embedded” in the so-called filter. The entire system consists of numerous thin and hollow tubes through which blood passes from the patient. The dialysis fluid flows in the opposite direction. Thus, a multiple increase in the contact surface between the blood and the dialysis fluid is achieved. Opposite directions are used to increase the gradient and thus increase the efficiency of hemodialysis.
What are the main methods of hemodialysis?
- Diffusion
Diffusion is the process by which salts dissolved in water move from a place of higher concentration to a place of lower concentration. Only substances for which the membrane is permeable can participate in diffusion, i.e. subject to “clearing” from the blood by the method of hemodialysis. These are, as a rule, water-soluble substances with a low molecular mass. This excludes lipid and protein molecules.
- Ultrafiltration
Ultrafiltration, through which excess water is removed from the body and, in particular, from the blood plasma. This happens due to a difference in pressures on both sides of the semi-permeable membrane, i.e. blood goes from a place of high pressure (the blood) to a place of low pressure (the dialysis fluid). The rate of ultrafiltration depends on several factors, such as the patient’s clinical condition, hemodynamic status, volume loading, respiratory status, water balance, presence of own diuresis, and others.
- Convection
Convection is the movement of water and salts dissolved in it through a semipermeable membrane along the hydrostatic gradient. The rate of convection depends on the size of the pores, the hydrostatic pressure, the volume, and the rate of ultrafiltration (in the absence of ultrafiltration there is little or no convection and vice versa).
What are the indications for starting hemodialysis?
Hemodialysis is indicated in children with chronic kidney disease, in which, as a result of kidney damage, there are:
- Volume burden as a result of the difficult excretion of water using the kidneys
- Presence of hyperkalemia, hyperammonemia, uremia, metabolic acidosis.
- Requirement of certain toxic substances, such as drugs or toxins, which cannot be removed by other medical means.
- Certain surgical conditions or congenital malformations prevent peritoneal dialysis.
The material is informative and cannot replace consultation with a doctor. Before starting treatment, you must consult a doctor.
