Peritoneal dialysis

Peritoneal dialysis is a safe and relatively inexpensive method of renal replacement therapy. The first attempt to replace renal function using this method in a patient with acute renal failure was made by Ganter in 1923. The abdominal cavity is created by nature itself as a reserve organ of detoxification. The peritoneum here serves as a semipermeable dialysis membrane, the area of which corresponds to the surface area of the patient's body, and the blood flow - to the renal blood flow (1200 ml / min). The clearance of low-molecular substances in peritoneal dialysis is significantly lower than in hemodialysis. Meanwhile, the peritoneal dialysis procedure is continuous (round the clock), and therefore the total clearance can be higher than in intermittent hemodialysis.

General characteristics

The process of peritoneal dialysis proceeds according to the same principles as dialysis through an artificial semi-permeable membrane using the "artificial kidney" apparatus; in this case, the peritoneum acts as a natural membrane. At the same time, the anatomical and physiological features of the peritoneum determine a number of fundamental differences in the capabilities of peritoneal dialysis from hemodialysis:

• The presence of mesenteric vessels in the peritoneum, which drain blood from the intestines into the portal system of the liver, increases the effectiveness of dialysis in cases of oral poisoning with hepatotropic drugs.
• The presence of a large amount of fatty tissue in the abdominal cavity creates conditions for effective dialysis of lipotropic toxicants that quickly concentrate in fat depots (chlorinated hydrocarbons, etc.) due to their direct washing with dialysis fluid.
• The presence of so-called hatches in certain places of the peritoneum provides the possibility of dialysis of not only crystalloids, but also large-molecular proteins, thereby creating conditions for the effective dialysis of toxicants that quickly and firmly bind to plasma proteins.

A decrease in blood pressure and the accompanying acidosis lead to an increase in the permeability of the capillary walls, which under these conditions makes it possible to maintain the dialysis process at a sufficient level.

Targeted change of physicochemical properties of dialysing solutions, in addition, allows to increase the efficiency of peritoneal dialysis taking into account similar features of toxicants. Alkaline dialysing solutions are most effective in case of poisoning with weakly acidic drugs (barbiturates, salicylates, etc.), acidic - in case of poisoning with poisons with properties of weak bases (chlorpromazine, etc.), as a result of which ionization of the toxic substance occurs, preventing its reabsorption from the dialysing solution into the blood, neutral dialysing solutions are most suitable for removing poisons with neutral properties (FOI, etc.). The possibility of using lipid peritoneal dialysis in cases of poisoning with fat-soluble drugs (dichloroethane) is being considered, and the addition of protein (albumin) to the dialysate fluid can increase the excretion of drugs that have a pronounced ability to bind to proteins (short-acting barbiturates, etc.), which depends on the sorption of the toxic substance on the surface of albumin, which allows maintaining a significant concentration gradient of the substance between the blood plasma and the dialysate solution until the surface of the adsorbent is completely saturated.

In acute exogenous poisoning, the fractional method of peritoneal dialysis is recommended, allowing for high intensity of toxic substance removal and at the same time ensuring constant control over the volume of introduced and removed dialysis fluid and its most complete contact with the peritoneum. In addition, the fractional method most effectively prevents such complications of peritoneal dialysis as abdominal cavity infection, large protein losses, and some others.

The fractional method involves sewing a special fistula with an inflatable cuff into the abdominal cavity using a lower midline laparotomy, and inserting a perforated catheter through the fistula between the peritoneal layers, through which the dialysate moves in both directions. Since the amount of dialysate that can be injected into the abdominal cavity at one time is limited (within 2 liters), the intensity of PD is maintained by regularly changing the dialysate at certain intervals (exposure). Due to this methodological feature of peritoneal dialysis, another approach to increasing its effectiveness is the correct choice of exposure. In this case, the exposure should be such as to ensure the maximum possible accumulation of the toxic substance in the dialysate fluid. An increase in exposure beyond the optimal period leads to resorption, or the reverse transition of the toxic substance into the blood, which significantly reduces the effectiveness of the operation.

In patients with acute renal failure, the effectiveness of any method of renal function substitution depends on the ultrafiltration rate. In peritoneal dialysis, its value is affected by the permeability of the peritoneum, osmolarity and exposure time of the dialysate, and the state of hemodynamics. When using solutions with a theoretical osmolarity of up to 307 mOsm/l, the ultrafiltration rate does not exceed 0.02 ml/kg x min). The use of high-osmolar solutions (up to 511 mOsm/l) makes it possible to increase it to 0.06 ml/kg x min). The principle of the peritoneal dialysis method is based on the diffusion mass transfer of fluid and substances dissolved in it from the vascular bed and surrounding tissues into the dialysate through a semipermeable membrane - the peritoneum. The rate of diffusion transport depends on the concentration gradient between the blood and the dialysate, the molecular weight of the substances and the resistance of the peritoneum. Naturally, the higher the concentration gradient, the higher the peritoneal transport rate, so frequent changes of dialysate in the peritoneal cavity can maintain a high level of mass transfer during the procedure.

The rate of ultrafiltration in peritoneal dialysis depends on the state of hemodynamics and the chosen therapy for circulatory failure. Theoretically, the blood flow in the peritoneal vessels is maintained at a satisfactory level even with a drop in systemic blood pressure. However, severe hemodynamic disturbances, centralization of blood circulation, infusion of significant doses of cardiotonics and vasopressors negatively affect the peritoneal blood flow and the rate of mass transfer. That is why, despite the fact that peritoneal dialysis can be effective in patients with unstable hemodynamics, the degree of effectiveness of the procedure in patients of this category, of course, decreases.

Many clinics around the world prefer "acute" peritoneal dialysis as renal replacement therapy in newborns and infants, given the minimal adverse effects of this method on hemodynamic parameters, the lack of need for vascular access and the use of systemic anticoagulation. Early initiation of dialysis in children with acute renal failure or multiple organ failure syndrome allows for rapid correction of water-electrolyte imbalance, metabolic disorders, clearance of exogenous and endogenous toxins, adequate volume of infusion-transfusion therapy and nutritional support during complex intensive therapy.

From a practical point of view, this method is simple and accessible to any intensive care unit, does not require complex and expensive equipment and high labor costs of personnel. However, despite all its advantages in pediatric practice, in some cases a situation arises that requires more dynamic correction of gross violations of water-electrolyte and metabolic balances. In hypervolemia, threatening pulmonary edema, critical hyperkalemia and lactate acidosis, neither technical difficulties, nor problems of adequate vascular access, nor a host of other important methodological issues can be a limitation for the use of extracorporeal detoxification methods in children.

Peritoneal dialysis technique for acute poisoning

Equipment	Fistula with inflatable cuff, perforated catheter (silicone, rubber), containers for dialysate solution
Highway system	The Y-shaped inlet line is connected to a dialysate collection container located above the patient's body level, and the outlet line is connected to a dialysate collection container located below the patient's body level.
Access to the abdominal cavity	Lower midline laparotomy, puncture insertion of a catheter
Volume of dialysate solution	1700-2000 ml, with a persistent tendency to fluid retention in the abdominal cavity - 850-900 ml
Temperature of dialysate solution	38 0-38 5 C. In case of hypo- or hyperthermia, the temperature of the dialysate solution can increase or decrease accordingly within 1-2 C.
Recommended modes	If laboratory monitoring is possible, peritoneal dialysis is stopped when the toxic substance disappears from the dialysate removed from the abdominal cavity. In the absence of laboratory monitoring, peritoneal dialysis is carried out until clear clinical signs of improvement in the patient's condition appear (in case of poisoning with psychotropic and hypnotic drugs - the onset of superficial sopor), in case of poisoning with chlorinated hydrocarbons, FOI and other poisons - at least 6-7 shifts, and in case of poisoning with psychotropic and hypnotic drugs, the number of shifts can be brought to 20-30 pH of the dialysis fluid in case of poisoning with phenothiazines, FOI and compounds of heavy metals and arsenic 7.1-7.2 - slightly acidic (addition of 15-25 ml of 4% sodium bicarbonate solution to 800 ml of dialysis fluid), in case of poisoning with noxiron 7.4-7.45 - neutral (25-50 ml of 4% sodium bicarbonate solution), and in case of poisoning with barbiturates and other poisons 8.0-8.5 - alkaline (150 ml of 4% solution sodium bicarbonate). In case of poisoning with heavy metal compounds and arsenic, 1 ml of a 5% solution of unithiol is added to each change of dialysate fluid, unithiol is also administered intravenously by drip at the rate of 200-250 ml of a 5% solution per day. The exposure of dialysate fluid in the abdominal cavity in case of poisoning with chlorinated hydrocarbons and heavy metal compounds and arsenic is 20 minutes, in case of poisoning with FOI - 25 minutes, in other cases - 30 minutes.
Indications for use	Laboratory critical concentrations in the blood of dialysable poisons with a pronounced affinity for proteins Clinical detoxification (exotoxic shock, pronounced hemolysis, etc.), poisoning with chlorinated hydrocarbons, aniline and other fat-soluble poisons with hepatotropic action
Contraindications	Extensive adhesions in the abdominal cavity. Foci of infection in the abdominal cavity. Pregnancy over 15 weeks. Tumors deforming the abdominal cavity.

Contraindications to peritoneal dialysis

Peritoneal dialysis cannot be performed after extensive abdominal surgeries, in the presence of diaphragmatic or inguinal hernias, etc.

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Complications of peritoneal dialysis

The most serious complication of peritoneal dialysis is peritonitis. Indeed, until the middle of the last century, this complication extremely limited the use of the method in clinical practice. However, since the 1970s, with the introduction of soft silicone catheters, commercial, factory-made dialysis solutions, modification of dialysis line connection locks and full compliance with asepsis and procedure rules, the risk of peritonitis has significantly decreased.

In addition, there is a risk of hypoproteinemia, since the possibility of protein loss during peritoneal dialysis (up to 4 g/day) has been proven, and hyperglycemia due to the use of high-osmolar (due to the high concentration of glucose) dialysate solutions.

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