Hemoperfusion is a therapeutic nephrology procedure used to remove toxic substances from the blood using a specific adsorption system. Adsorption describes the accumulation of substances from gases or liquids on the surface of a solid. Detoxification by hemoperfusion represents an extracorporeal (outside the body) blood purification procedure, the operation of which is based on the binding capacity of the adsorption medium used for the individual toxic substances.
Indications (areas of application)
- Removal of toxic substances from the blood. The following conditions must be met:
- Toxin amount in the blood – only if the concentration of the toxic substance in the bloodstream is sufficient, the use of hemoperfusion can be considered useful. For toxins that accumulate primarily in fat, brain or bone, an extracorporeal blood purification procedure will not achieve a sufficient effect.
- Clearance – the toxin present in the blood must be measurably removed by hemoperfusion. The elimination ability of hemoperfusion must be determined for each toxin. The choice of blood purification procedure depends on the physical properties of the toxin. For diverse toxins, a combination of several procedures is useful. The procedure
Unlike other detoxification procedures, toxin elimination does not occur by diffusion or convection. Used hemoperfusion in the removal of exogenous (externally supplied) toxins that can not be adequately eliminated from the body by hemodialysis or hemofiltration. Adsorption media
Both coated activated carbon and neutral resins can be used as adsorption media in hemoperfusion because both substances are capable of surface enlargement. This surface enlargement massively increases the number of toxin binding sites. This high number of binding sites is achieved via granule-like (grain-like) particle structures with uneven surfaces. To achieve a sufficient effect in hemoperfusion, between 70 and 300 grams of the adsorption granules are included in the hemoperfusion cartridges. Activated carbon
- The surface area of 300 grams of coated activated carbon is equivalent to approximately 400,000 square meters.
- The patient’s blood is now introduced into this cartridge filled with activated carbon via a blood inlet. After successful filling of the cartridge, the toxins contained in the blood are irreversibly (not to be reversed) removed from the blood. After the blood has been purified, it leaves the cartridge through a special blood outlet and is reintroduced into the patient’s bloodstream. Elimination of toxins by the adsorbent medium in the cartridge can continue until saturation (lack of binding ability) of the binding site for the toxins occurs. Replacement of the cartridge is then necessary for further hemoperfusion.
- As described earlier, the principle of hemoperfusion is based on surface enlargement of the activated carbon or neutral resins. The activated carbon can be made either from biological materials such as peat or coconut shell carbon, or from non-biological elements such as various types of geological coal. However, in order for activated carbon to enter an activated state, it must be oxidized in air or in an environment rich in water vapor. Oxidation represents a chemical reaction in which a substance gives up electrons, which are then absorbed by another molecule. Without this activation, the necessary binding ability of toxins would not exist. In order for the toxins contained in the blood to bind at all, the blood flow must pass through the remaining cavities of the activated carbon.
The coating of the activated carbon is of great importance in detoxification by hemoperfusion, because in the absence of a coating, the risk of life-threatening embolism due to the rough surface of the activated carbon is relatively high. In addition, severe thrombocytopenias (reduction in the number of platelets) and leukopenias (reduction in the number of white blood cells) may occur. The possibility of the development of hemolysis (destruction and dissolution of red blood cells) is also given by the surface properties of uncoated activated carbon.However, the coating not only reduces these risk factors, it also creates a barrier for proteins (protein) so that there is no protein loss for the human organism. A commonly used coating material is cellulose. Synthetic resins
The use of special synthetic resins in hemoperfusion is based on the fact that both neutral resins and ionic resins can bind lipophilic (fat-loving) toxins in particular, thus helping to clarify the blood. Polystyrene can be mentioned as an example substance for synthetic resins. Performance of hemoperfusion
- Before starting detoxification therapy by hemoperfusion, the primary step is to check whether the cartridge is sterile. If this is not the case, steam sterilization must be performed beforehand.
- To achieve adequate detoxification, a blood flow of 200 to 300 ml per minute must be aimed for. Depending on a possible heparin coating, the cartridge may need to be flushed with heparin-laced saline. Irrespective of this, administration of heparin into the arterial leg of the tubing system is indicated. However, it should be borne in mind here that heparin is withdrawn from the blood by the adsorption properties of activated carbon, so that the concentration of effect is changed.
- To avoid possible hypoglycemia, the cartridge should be preflushed with 5% glucose solution before hemoperfusion.
Possible complications
- Blood pressure drop – due to adsorption of blood pressure regulating hormones such as norepinephrine or even angiotensin, blood pressure drops significantly at the beginning of the therapeutic intervention. The drop in blood pressure can be exacerbated by bloodletting into the system in the case of primarily unstable blood pressure. Therefore, substitution with plasma expanders should possibly be performed in the first hour of therapy.
- Thrombocytopenia – as previously listed, hemoperfusion may result in a loss of platelets in the blood. As a sign of the body’s counter-regulation is the increased occurrence of young platelets. The consequence of this thrombocytopenia can be a massive bleeding complication. If one examines the activated carbon after hemoperfusion has taken place, it can be seen that a dense felt of fibrin and platelets is detectable in the carbon particles.
- Reduction in the number of immunoglobulins – immunoglobulins are antibodies whose quantity in the blood is reduced by hemoperfusion. The exact mechanism is still unclear, but an increase in bronchopneumonia (pneumonia) has been observed in hemoperfused patients despite successful elimination of toxins from the blood.
- Adsorption of drugs – Because the risk of occurrence of pneumonia is significantly increased by hemoperfusion, the affected patients should benefit from antibiotic therapy. However, it should be considered problematic that antibiotics can be bound by the adsorption medium in addition to toxins. The binding to the medium reduces the effective serum level of the antibiotic, so that the effect of the treatment cannot be guaranteed. So far, no meaningful in vivo studies (study conducted on volunteers) have been conducted to prove this effect, however, in vitro (study in the test tube) it has been demonstrated that, for example, the antibiotic ampicillin was 100% removed from the blood after three hours of hemoperfusion.
