Classic hemodialysis

Under experimental conditions, the possibility of extracorporeal cleansing of the blood with the use of hemodialysis was first shown by Abel in 1913. But only 30 years later WJ Kolff constructed a device that proved to be suitable for clinical conditions. Since then, this procedure has become firmly established in clinical practice for the programmatic treatment of patients with chronic uremia. The term classical hemodialysis should be understood as intermittent therapy (with a duration of no more than 3-4 hours), with a frequency of 3 times a week, using high blood flow rates (250-300 ml / min), dialysis solution (up to 30 l / h) and " dose "dialysis (Kt / V, at least more than 1).

The instability of hemodynamics with the use of standard hemodialysis in resuscitation patients is due to the speed and volume of ultrafiltration, the decrease in osmolarity of the plasma. Such instability develops at the beginning of a session of intermittent dialysis due to changes in intravascular volume and development of hypovolemia. In the classic case of acute renal failure, there is a conflict between body overload with fluid (in the form of tissue edema, ascites, effusion into the pleural and abdominal cavities) and intravascular hypovolemia. This contributes to hypotension when performing fast and volumetric ultrafiltration. The factor limiting the volume of filtration is the velocity of fluid transport between the extra- and intravascular spaces. Many patients at this rate are affected by changes in capillary permeability due to inflammation, as well as disturbances of colloid osmotic pressure of the plasma in response to hypoalbuminemia and / or electrolyte imbalance.

Classical hemodialysis is characterized by the diffusion transfer of osmotically active substances from the blood into dialysate due to the concentration gradient. Since water transport is more active, in normal hemodialysis plasma osmolality decreases. This causes an even greater decrease in the volume of extracellular fluid that rushes into the cell. An increase in the duration of hemodialysis and a decrease due to this speed and volume of ultrafiltration, as well as the ability to regulate the concentration of sodium in dialysate, helps to prevent the development of intra-dialysis hypotension.

Stabilization of hemodynamic parameters depends on the temperature of dialyzing and replacing solutions. The use of cool solutions prevents arterial hypotension due to moderate vasoconstriction and increased total peripheral vascular resistance. But pronounced vasoconstriction worsens tissue perfusion and heart function.

The question of the use of biocompatible membranes in the process of such a procedure as classical hemodialysis is relevant. According to the results of the research, the use of cellulose membranes leads to activation of the complement system, leukocytes and other humoral and cellular mechanisms that cause coagulation disorders, allergies, inflammatory and immune damages. Therefore, the use of synthetic, biocompatible membranes (for example, polysulfone, AN-69) greatly optimizes the course of the procedure.

The use of intermittent hemodialysis in patients with acute renal failure is warranted, in which fast and effective filtration of uremic toxins is necessary, correction of water-electrolyte balance and CBS. If low-molecular substances, which include creatinine, urea, potassium, can be effectively removed by various methods of blood purification, then rapid correction of metabolic acidosis without the danger of hypernatremia and water balance disorders is much easier to perform using the bicarbonate dialysis procedure.

On the other hand, classical hemodialysis in the treatment of acute renal failure in critically ill patients of the intensive care unit is deeply "nonphysiological", since it involves aggressive short-term treatment, with large intervals (more than a day) between procedures. This feature of the procedure determines the development of hemodynamic instability and insufficient control of uremic intoxication, water-electrolyte, acid-base and calcium-phosphorus balances. Moreover, the use of the "classical" hemodialysis technique in intensive care units does not allow adequate nutritional support, as liquid overload and the development of pulmonary edema in interdialytic spaces are possible. Complications of this method of intensive dialysis include a rapid decrease in the concentration of dissolved substances (osmotically active sodium and urea), which leads to significant changes in the water content in the brain tissues and increased intracranial pressure in patients at risk of development or with an already developed edema of the brain.

Thus, classical hemodialysis is not the best method of treatment of acute renal failure and in conditions of intensive care unit. In the traditional version, this method of substitutive renal therapy is not able to provide either safety or proper efficacy of therapy in critically ill patients. The high incidence of complications noted in recent years has led to the development and implementation of new methods and methods of renal replacement therapy with greater hemodynamic stability, the absence of neurological complications, better control of the state of water-electrolyte and acid-base balance, and also enabling adequate nutritional support for patients in intensive care units.

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