Hemodialysis for acute poisoning

Dialysis is a method of removing toxic substances (electrolytes and non-electrolytes) from colloidal solutions and solutions of high-molecular substances, based on the properties of some membranes to pass molecules and ions, but retain colloidal particles and macromolecules. From a physical point of view, hemodialysis is free diffusion combined with filtration of a substance through a semi-permeable membrane.

The membranes used for dialysis can be divided into two main types: artificial (cellophane, cuprophane, etc.) and natural (peritoneum, glomerular basal membrane, pleura, etc.). The size of the membrane pores (5-10 nm) allows only free molecules that are not bound to protein and are suitable in size for the pore size of the membrane to penetrate through them. Only the concentration of the non-protein-bound part of the toxic substance is the initial one for the quantitative assessment of the possible effect of any dialysis, since it characterizes the ability of the chemical substance to pass through artificial or natural membranes, or its "dialyzability". Of decisive importance for the dialyzability of a chemical substance are the features of its physicochemical and toxicological properties, the influence of which on the efficiency of hemodialysis is formulated as follows:

• The toxicant must be relatively low molecular weight (molecule size should be no more than 8 nm) to diffuse freely through the semipermeable membrane.
• It must be soluble in water and present in the plasma in a free, non-protein-bound state, or this bond must be easily reversible, i.e., when the concentration of free toxicant decreases during dialysis, it must be continuously replenished by releasing it from its protein bond.
• The toxicant must circulate in the blood for a certain time, sufficient to connect the “artificial kidney” apparatus and pass several BCCs through the dialyzer, i.e. at least 6-8 hours.
• There must be a direct relationship between the concentration of the toxicant in the blood and the clinical manifestations of intoxication, which determines the indications for hemodialysis and its duration.

To date, despite the large number of types of “artificial kidney” devices, the principle of their operation has not changed and consists of creating blood and dialysate flows on both sides of a semi-permeable membrane - the basis for the operation of dialysers-mass exchange devices.

The dialysate fluid is prepared in such a way that its osmotic, electrolyte characteristics and pH basically correspond to the level of these indicators in the blood; during hemodialysis it is heated to 38-38.5 °C, in this case its use does not lead to homeostasis disorders. The change in the standard parameters of the dialysate fluid is carried out according to special indications. The transfer of the toxicant from the blood to the dialysate fluid occurs due to the difference (gradient) of its concentrations on both sides of the membrane, which requires a large volume of dialysate fluid, which is constantly removed after passing through the dialyzer.

Hemodialysis is considered a highly effective method of detoxification in cases of acute poisoning with many drugs and chlorinated hydrocarbons (dichloroethane, carbon tetrachloride), compounds of heavy metals and arsenic, alcohol substitutes (methanol and ethylene glycol), which, due to their physicochemical properties, have sufficient dialysability.

It should be borne in mind that when treating with hemodialysis, it is necessary to dynamically determine the relationship between the clinical manifestations of poisoning and the concentration of the toxicant in the blood, which is most noticeable when exposed to psychotropic substances and can change as follows:

• Positive dynamics of clinical data during hemodialysis is accompanied by a significant decrease in the concentration of the toxicant in the blood, which indicates a favorable course of the disease, which is usually observed with the early use of HD on the first day of treatment.
• Positive clinical dynamics are not accompanied by a parallel decrease in the concentration of the toxicant in the blood. Improvement of clinical data in this group of patients can be explained by the favorable effect on oxygen transport created by the "artificial kidney" apparatus, which is confirmed by the corresponding studies of the gas composition of the blood. Some deterioration in the clinical condition and a parallel slight increase in the concentration of the toxicant are noted in some patients of this group 1-5 hours after hemodialysis. This is obviously due to its continued entry from the gastrointestinal tract or equalization of its concentration in the blood with the concentration in other tissues of the body.
• A noticeable decrease in the concentration of the toxicant in the blood is not accompanied by positive clinical dynamics. It occurs with the development of multiple organ failure.

Filtration modifications of hemodialysis in the toxicogenic stage are used in cases, as a rule, of late admission of patients, when, along with the removal of toxicants from the blood, there is a need to correct changes in homeostasis parameters that arise as a result of long-term hypoxic and metabolic disorders.

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Hemodialysis technique for acute poisoning

Equipment	Artificial kidney machine
Mass transfer device	Dialyzer
Highway system	Disposable special
Vascular access	Catheterization of the main vein with a double-lumen catheter using the subclavian vein - followed by X-ray examination of the chest organs
Preliminary preparation
Hemodilution	12-15 ml of fluid per 1 kg of the patient's body weight until the hematocrit decreases within 35-40% and the central venous pressure reaches about 80-120 mm Hg
Heparinization	500-1000 IU/h of sodium heparin per 1 kg of patient's body weight. In case of risk of bleeding - dosed heparinization with a 1.5-2 times reduction in the dose of sodium heparin with its constant intravenous drip administration in isotonic glucose or electrolyte solutions or regional heparinization with inactivation of sodium heparin with protamine sulfate at the outlet of the dialyzer
Blood perfusion rate	150-200 ml/min (within the doubled clearance of the toxic substance) with a gradual increase in the perfusion rate to the required level over 10-15 minutes
Blood perfusion volume	From 36 to 100 l per hemodialysis session (5-15 BCC)
Indications for use	Clinical poisoning with dialyzable poisons, drugs, chlorinated hydrocarbons, methanol, ethylene glycol, heavy metals, arsenic. Laboratory presence of critical concentrations of dialyzable poisons in the blood, pronounced clinical picture of poisoning with poisons circulating in the blood for a long time.
Contraindications	Hypotension refractory to therapy and administration of vasopressors. Gastrointestinal and visceral bleeding.
Recommended modes	The duration of one hemodialysis session is not less than 6-8 hours. In case of barbiturate poisoning, it can be increased (up to 12-14 hours) based on laboratory data or positive neurological dynamics before the onset of superficial stupor. In case of severe poisoning with heavy metal compounds and arsenic, hemodialysis continues for 10-12 hours for complete blood purification. The consumption of unithiol in case of moderately severe poisoning with heavy metal compounds and arsenic is 20-30 ml/h, in case of severe poisoning - 30-40 ml/h of 5% solution, ethanol in case of ethylene glycol and methanol poisoning - 2-3 ml of 96% solution per 1 kg of patient's body weight (in a tenfold dilution in 5 or 10% glucose solution). In case of poisoning with foliar-organic substances, the doses of antidotes (atropine, cholinesterase reactivators) are increased by 2-3 times. If laboratory control is possible, the antidote is dosed so that its content in the blood exceeds the level of poison in it. If the concentration of the toxic substance in the blood increases or the clinical picture of poisoning persists after the end of hemodialysis, its sessions are repeated. In case of poisoning with FOI, the number of hemodialysis reaches 4-10 - until the blood is cleansed of toxic metabolites and the beginning of stable restoration of AChE. In case of severe poisoning, the method of choice is prolonged hemodialysis (several days - a week)