Renal replacement therapy

Replacement renal therapy reduces uremic intoxication and maintains the "internal environment" in a state as close as possible to the physiological state, without adversely affecting the functions of the patient's vital organs and systems.

Severe acute renal failure contributes to an increase in lethality and is associated with an overall increase in this index to 50-100%. Renal dysfunction develops most often as a consequence of another existing pathology (eg, low cardiac output, infectious-septic complications), which is the cause of death of patients. Methods of extracorporal therapy should be considered as an interim treatment that allows a patient to survive the period until the restoration of the functioning of his own kidneys. In the case of acute renal dysfunction or multiple organ dysfunction syndrome, severe uraemia, hyperkalemia, or severe metabolic acidosis should not be tolerated , since each of these complications can significantly affect the final result of treatment, which necessitates the use of renal replacement therapy at earlier stages.

[1], [2], [3], [4], [5], [6], [7], [8]

Indication for renal replacement therapy

Given the apparent identity of the indications for renal replacement therapy in patients with terminal stage of chronic renal failure and in patients with acute renal failure, it is of fundamental importance to include methods of extracorporeal detoxification as soon as possible into complex intensive therapy. In intensive care units, extracorporeal methods of blood purification are used to a greater extent to maintain the function of the kidneys and other vital organs (heart, lungs, CNS) than to replace them. It is necessary, with the help of renal replacement therapy, to provide optimal treatment without adversely affecting the functions of the patient's organs and systems without impeding the adequate restoration of kidney activity.

Indications for renal replacement therapy:

• Non-obstructive oliguria (diuresis <200 ml / 12 h).
• Anuria / severe oliguria (diuresis <50 ml / 12 h).
• Hyperkalemia (K +> 6.5 mmol / l) or a rapid increase in the level of K + -plasma.
• Severe disinatraemia (115
• Pronounced acidemia (pH <7.1).
• Azotemia (urea> 30 mmol / l).
• Clinically significant edema of organs and tissues (especially pulmonary edema).
• Hyperthermia (t> 39.5 ° C).
• Complications of uremia (encephalopathy, pericarditis, neuro- and myopathies).
• Overdose of medicines.

"Out-of-the-box" indications (sepsis, congestive heart failure, etc.). There are no special criteria for conducting renal replacement therapy in critically ill patients to date. To the question of indications for the use of methods of detoxification in patients with intensive care should be treated in a comprehensive manner, assessing the overall state of homeostasis and the function of vital organs. In patients with ARI, it is preferable to prevent physiological disorders of organs and systems, than to restore their functions later. Modern methods of detoxification can safely and efficiently perform blood purification in critically ill patients and make it possible to differentiate the choice of the method of renal replacement therapy in order to improve the quality and optimize the results of treatment of patients.

Methods of renal replacement therapy

Replacement renal therapy has the following types: hemodialysis, peritoneal dialysis, permanent hemofiltration or hemodiafiltration, "hybrid" methods of replacement of kidney function. The capabilities of these methods depend on the clearance of substances with different molecular weights, membrane properties, blood flow velocity, dialysis solution and ultrafiltration.

It is known that all substances can be divided into 4 large groups depending on the value of their molecular weight:

• low-molecular substances with a mass not exceeding 500-1500 D, they include water, ammonia, K \ Na +, creatinine, urea;
• medium molecular weight - with a mass of up to 15 000 D: mediators of inflammation, cytokines, oligopeptides, hormones, fibrin degradation products;
• substances of relatively large molecular weight - up to 50 000 D: myoglobin, beta2-microglobulins, blood clotting system degradation products, lipoproteins;
• large-molecular substances with a mass exceeding 50 000 D: hemoglobin, albumins, immune complexes, etc.

In hemodialysis, a diffusion mechanism of mass transfer is used, in which the osmotic pressure gradient on both sides of the semipermeable membrane is of primary importance. The diffusion mechanism of transport is best suited for the filtration of low-molecular substances, in a large amount dissolved in plasma, and it is less effective with increasing molecular weight and lowering the concentration of removed substances. The effectiveness of peritoneal dialysis is based on the transport of water and dissolved substances through the peritoneum, due to diffusion and ultrafiltration, due to the gradients of osmotic and hydrostatic pressures.

At the heart of hemofiltration and plasma exchange are the principles of ultrafiltration (through a highly permeable membrane) and convection, and the transport of substances is carried out at the expense of the gradient of hydrostatic pressure. Hemofiltration is, first of all, a convective technique in which the ultrafiltrate is either partially or completely replaced by sterile solutions administered either before the filter (pre-dilution) or after the filter (post-dilution). The most important positive aspect of hemofiltration is the possibility of removing so-called medium molecules involved in the pathogenesis of sepsis and multiple organ failure. These molecules have a sufficiently large molecular weight and are contained in the plasma in low concentrations and, therefore, because of the low osmotic gradient, can not be removed by the diffusion mechanism of mass transfer. If necessary, more efficient and rapid removal of low molecular weight substances in patients with hypercatabolism, which is often observed in intensive care units, use the principle of combining convection and diffusion, for example, during hemodiafiltration. This method is a combination of hemofiltration and hemodialysis, it uses a counterflow of dialysate to the flow of blood in the hemofiltration circuit. And, at last, at a hemoperfusion use a principle of concentration of substances on a surface of the sorbent.

Which method of blood purification and replacement renal therapy is most preferable: intra- or extracorporeal? Continued or intermittent? Diffusion or convection? It is extremely difficult to answer these questions, since the effectiveness of any therapy depends on the complex of components, primarily the clinical condition of patients, their age and body weight, the technical support and the park of equipment for performing renal replacement therapy in the clinic, as well as the experience and specialization of the clinician (nephrologist or resuscitator) and much more.

Permanent renal replacement therapy, as a rule, is held around the clock. This determines the possible side effects.

• The risk of bleeding increases with the constant use of systemic anticoagulation. In patients with compromised blood coagulation, especially in the postoperative period, this complication can be fatal.
• The concentration of inotropic drugs, antibiotics and other expensive drugs decreases with constant ultrafiltration or adsorption on the filter membrane.
• Inadequate correction of uremia, especially in patients with hypercatabolism.
• Round-the-clock replacement renal therapy makes it difficult to conduct diagnostic and treatment procedures, increases the need for sedatives and limits the mobility of patients.
• High cost and labor intensity of treatment, especially in cases of severe sepsis and multiple organ dysfunction syndrome, when performing high-volume procedures (ultrafiltration> 6 l / h).

Hybrid technologies of renal replacement therapy

"Hybrid" technologies are a slow, low-effective daily dialysis (SLEDD-Sustained low-efficiency daily diafiltration), which prevents the negative impact of intermittent treatment on hemodynamics by removing the liquid and dissolved substances in it for a long time exceeding 4 hours. This avoids rapid fluctuations in the concentration of dissolved substances and reduce intravascular volume. The method allows to increase the dose of dialysis in patients with multiple organ dysfunction and a high level of catabolism. The increase in the dose, and consequently, the effectiveness of intermittent replacement renal therapy is possible due to the lengthening of the procedure for more than 3-4 hours, as well as to increase the diffusion component of treatment.

Thus, "hybrid" technologies allow:

• adjust the treatment to the condition of patients, combining the therapeutic goals of permanent replacement renal therapy and periodic hemodialysis;
• ensure a low rate of ultrafiltration and achieve a stable hemodynamic index;
• conduct a low-efficiency removal of dissolved substances and reduce the risk of developing a syndrome of imbalance and progression of brain swelling phenomena;
• increase the duration of the daily procedure to increase the dose and effectiveness of dialysis;
• carry out diagnostic and therapeutic procedures;
• reduce the daily dose of systemic anticoagulation and reduce the total cost of replacement renal therapy.

To conduct "hybrid" methods, standard dialysis machines (with an obligatory system for water purification) using low blood flow velocities (100-200 ml / min) and dialysate flow (12-18 l / h) are used.

Treatment should be daily and prolonged (more than 6-8 hours), with the ability to prepare on-line replacement solution and dialysate. Depending on the type of extracorporeal procedure required (hemodialysis, haemofiltration or hemodiafiltration), biocompatible, synthetic high permeability membranes should be used for SIEDD therapy. Taking into account the violations of the coagulating blood system in the postoperative period, the use of "hybrid" technologies allows the use of minimal doses of anticoagulants [2-4 U / kg / h) of heparin] or procedures without systemic anticoagulation. The use of SLEDD-therapy at night allows for carrying out various diagnostic studies and therapeutic manipulations during the day. In addition, nighttime SLEDD therapy allows for hemodialysis in the daytime for other patients on the same device.