Classical hemodialysis

In experimental conditions, the possibility of extracorporeal blood purification using hemodialysis was first demonstrated by Abel in 1913. But it was not until 30 years later that W. J. Kolff constructed a device that was suitable for clinical conditions. Since then, this procedure has firmly entered clinical practice for the programmatic treatment of patients with chronic uremia. The term classical hemodialysis should be understood as intermittent (lasting no more than 3-4 hours) therapy, with a frequency of 3 times a week, using high blood flow rates (250-300 ml/min), dialysate (up to 30 l/h) and dialysis "dose" (Kt/V, at least more than 1).

Hemodynamic instability during standard hemodialysis in intensive care patients is caused by the rate and volume of ultrafiltration and a decrease in plasma osmolarity. Such instability develops at the beginning of an intermittent dialysis session due to changes in intravascular volume and the development of hypovolemia. In the classic case of acute renal failure, a conflict arises between fluid overload of the body (in the form of tissue edema, ascites, effusion in the pleural and abdominal cavities) and intravascular hypovolemia. This contributes to hypotension during rapid and volumetric ultrafiltration. The factor limiting the filtration volume is the rate of fluid transport between the extra- and intravascular spaces. In many patients, this rate is affected by changes in capillary permeability due to inflammation, as well as disturbances in the colloid osmotic pressure of plasma in response to hypoalbuminemia and/or electrolyte imbalance.

Classic hemodialysis is characterized by diffusion transfer of osmotically active substances from the blood to the dialysate due to the concentration gradient. Since water transport is more active, the plasma osmolarity decreases during conventional hemodialysis. This causes an even greater decrease in the volume of extracellular fluid that rushes into the cell. Increasing the duration of hemodialysis and the resulting decrease in the rate and volume of ultrafiltration, as well as the ability to regulate the concentration of sodium in the dialysate, helps prevent the development of intradialytic hypotension.

Stabilization of hemodynamic parameters depends on the temperature of the dialysing and substituting solutions. The use of cool solutions prevents arterial hypotension due to moderate vasoconstriction and an increase in total peripheral vascular resistance. However, severe vasoconstriction worsens tissue perfusion and cardiac function.

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

The use of intermittent hemodialysis in patients with acute renal failure, which requires rapid and effective filtration of uremic toxins, correction of water-electrolyte balance and acid-base balance, is justified. If low-molecular substances, which include creatinine, urea, potassium, can be effectively removed using various blood purification methods, then rapid correction of metabolic acidosis without the risk of developing hypernatremia and water balance disorders is much easier to achieve 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 "non-physiological", since it involves aggressive short-term treatment, with large intervals (more than a day) between procedures. This feature of the technique causes 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 for adequate nutritional support, since fluid overload and the development of pulmonary edema in interdialysis intervals are possible. Complications of this intensive dialysis technique 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 brain tissue and an increase in intracranial pressure in patients at risk of developing or with already developed cerebral edema.

Thus, classical hemodialysis is not the best method for treating acute renal failure in the intensive care unit. In its traditional version, this method of renal replacement therapy is unable to ensure either safety or the proper effectiveness of therapy in patients in critical condition. The high frequency of complications noted in recent years has led to the development and implementation of new methods and techniques of renal replacement therapy that have greater hemodynamic stability, no neurological complications, better control of the water-electrolyte and acid-base balance, and also make it possible to provide adequate nutritional support to patients in intensive care units.

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