Hemodialysis in 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 certain membranes, to pass molecules and ions, but to retain colloidal particles and macromolecules. From a physical point of view, hemodialysis is a free diffusion, combined with the filtration of the substance through a semi-impermeable membrane.

The membranes used for dialysis can be divided into two main types of artificial (cellophane, cuprofan, etc.) and natural (peritoneum, basal membrane of the glomeruli of the kidneys, pleura, etc.). The pore size of the membranes (5-10 nm) makes it possible to penetrate through them only to free molecules that are not bound to a protein and which are suitable in size to the pore size of a given membrane. Only the concentration of the non-protein part of the toxic substance is the starting point for quantifying the possible effect of any dialysis, as it characterizes the ability of the chemical to pass through artificial or natural membranes, or its "dialyzability". Critical to the dialysability of a chemical substance are the features of its physicochemical and toxicological properties, the effect of which on the effectiveness of hemodialysis is formulated as follows:

• The toxicant should be relatively low molecular (the molecule size should not be more than 8 nm) for free diffusion through the semi-impermeable membrane.
• It must dissolve in water and be in the plasma in a free, non-protein-bound state, or this bond must be easily reversible, ie, when the concentration of the free toxicant decreases during dialysis, it must be continuously replenished by the release of its association with the protein.
• The toxicant should circulate in the blood for a certain time, sufficient to connect the device "artificial kidney" and pass through the dialyzer of several bcc, at least 6-8 hours.
• There must be a direct relationship between the concentration of toxicant in the blood and the clinical manifestations of intoxication, which determine the indications for hemodialysis and its duration.

To date, despite the large number of types of "artificial kidney" devices, the principle of their work has not changed and is concluded in the creation of blood flows and dialysating fluid on both sides of the semi-impermeable membrane - the basis for the work of dialyzers-mass exchange devices.

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

Hemodialysis is considered a highly effective method of detoxification in acute poisoning by many drugs and chlorinated hydrocarbons (dichloroethane, carbon tetrachloride), heavy metal and arsenic compounds, alcohol substitutes (methanol and ethylene glycol), which have sufficient dialyzability for their physicochemical properties.

It should be borne in mind that in the treatment 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:

• The positive dynamics of clinical data during hemodialysis is accompanied by a marked decrease in the concentration of toxicant in the blood, which indicates a favorable course of the disease, which is usually observed in the early application of HD in the first day of treatment.
• Positive clinical dynamics are not accompanied by a parallel decrease in the concentration of toxicant in the blood. Improvement of clinical data in this group of patients can be explained by the favorable effect on the transport of oxygen produced by the "artificial kidney" apparatus, which is confirmed by appropriate studies of the gas composition of the blood. A part of patients of this group, after 1-5 h after hemodialysis, notice a certain deterioration in the clinical state and in parallel a slight increase in the concentration of the toxicant. This is obviously due to its continued intake from the gastrointestinal tract or by equalization of its concentration in the blood with concentration in other tissues of the body.
• A marked decrease in the concentration of the toxicant in the blood does not accompany the positive clinical dynamics. It occurs with the development of multiorgan insufficiency.

Filtration modifications of hemodialysis in the toxicogenic stage are used in cases, as a rule, of late admission of patients, when along with removal of toxicants from the blood, there is a need to correct the changes in homeostatic indices resulting from prolonged hypoxic and metabolic disorders.

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

The method of hemodialysis in acute poisoning

Equipment	Apparatus "artificial kidney"
Mass-exchange device	Dialyzer
System of highways	One-time special
Vascular access	Catheterization of the main vein with a double-lumen catheter using a subclavian vein - followed by chest X-ray examination
Preliminary preparation
Hemodilution	12-15 ml of liquid per 1 kg of the body weight of the patient to a decrease in hematocrit in the range of 35-40% and reaching a CVP of the order of 80-120 mm Hg
Heparinization	500-1000 IU / h of sodium heparin per 1 kg of body weight of the patient. At the risk of bleeding - dosed heparinization with a decrease in the dose of heparin sodium in 1 5-2 times with its constant intravenous drip in isotonic solutions of glucose or electrolytes, or regional heparinization with the inactivation of heparin sodium protamine sulfate at the outlet of the dialyzer
Blood perfusion rate	150-200 ml / min (within twice the clearance of a toxic substance) with a gradual increase in the perfusion rate to the required within 10-15 min
Blood perfusion volume	From 36 to 100 liters per one hemodialysis session (5-15 bcc)
Indications for use	Clinical poisoning with dialyzing poisons of drugs, chlorinated hydrocarbon, methanol, ethylene glycol, heavy metals, arsenic. Laboratory presence in the blood of critical concentrations of dialyzing poisons, a pronounced clinical picture of poisons poisoning, long circulating in the blood.
Contraindications	Refractory to therapy and the introduction of vasopressors hypotension. Gastrointestinal and cavitary bleeding.
Recommended Modes	The duration of a single hemodialysis session is at least 6-8 hours. When barbiturates are poisoned, it can be increased (up to 12-14 hours) according to laboratory data or with positive neurological dynamics before the onset of the superficial sopor. In severe poisoning with heavy metal compounds and arsenic, hemodialysis lasts 10-12 hours for complete purification of the blood. The consumption of unithiol in case of moderate poisoning with heavy metals and arsenic compounds is 20-30 ml / h, for heavy - 30-40 ml / h 5% solution, ethanol for poisoning with ethylene glycol and methanol - 2-3 ml of 96% solution per 1 kg of weight body of the patient (in a tenfold dilution in a 5 or 10% solution of glucose). When poisoning FOI doses of antidotes (atropine, cholinesterase reagents) increase by 2-3 times. If the laboratory control is possible, the antidote is dosed so that its content in the blood exceeds the level of the poison in it. When the concentration of toxic substance in the blood increases or the clinical picture of poisoning is maintained after the end of hemodialysis, its sessions are repeated. With FOI poisoning, the number of hemodialysis reaches 4-10 - before the blood purification from toxic metabolites and the beginning of a steady recovery of AChE. With severe poisoning, the method of choice is prolonged hemodialysis (several days a week)