Why the need for blood substitutes arose
Sources of whole donor blood and its individual components are extremely limited. At the same time, the need for transfusion therapy is continuously growing. This is due to the active development of surgical practice, in particular — the introduction of complex surgical interventions and the use of artificial blood circulation apparatuses.
The use exclusively of cadaveric or utilized blood cannot completely solve the problem of global shortage. Thanks to the development of modern methods of chemistry and enzymology, mass production of artificial preparations has become possible. Today they are produced from available raw materials, yielding synthetic, polysaccharide, and heteroprotein transfusion media capable of temporarily taking over the functions of plasma or formed elements.
Medical requirements for preparations
For a solution to be used safely in the patient's bloodstream, it must meet a number of strict criteria. There are five main requirements for modern blood-substituting liquids:
- Physicochemical similarity. The medium must be as close as possible to natural blood plasma in its physical and chemical characteristics.
- Biodegradation and elimination. After performing its function, the preparation must be completely eliminated from the body or metabolized by natural enzyme systems.
- Absence of sensitization. The solution must not provoke allergic or immune reactions upon repeated intravenous administrations.
- Atoxicity. Any toxic damaging effect on the organs and tissues of the patient is excluded.
- Stability. Preparations must withstand the sterilization process and retain their basic biological and physicochemical properties during long-term storage.
Classification by chemical composition
Depending on the base active substance and structure, all blood substitutes are divided into several large groups:
- Colloid solutions. Include dextrans with an average molecular weight from 30,000 to 70,000, as well as various gelatin-based preparations.
- Hydroxyethyl starch preparations. Represented by hydroxyethyl starch solutions.
- Saline solutions. The most well-known representatives are isotonic sodium chloride solution and complex Ringer-Locke solution.
- Buffer solutions. These include sodium bicarbonate and trometamol solutions.
- Solutions of polyhydric alcohols and sugars. Include dextrose, fructose, and sorbitol.
- Protein preparations. Various amino acid solutions and protein hydrolysates.
- Fat preparations. Specialized fat emulsions, which usually include triglycerides and soybean oil.
Division by target action
In clinical practice, the classification based on the main therapeutic effect of the transfusion medium is the most convenient. According to this principle, five groups are distinguished:
- Hemodynamic (antishock). Designed to maintain blood pressure and circulating blood volume. These include low- and medium-molecular-weight dextrans, gelatin preparations, and hydroxyethyl starches. Some solutions are combined with mannitol and sodium chloride.
- Detoxification. Used for binding and excreting toxins. A typical representative is low-molecular-weight polyvinyl alcohol.
- Parenteral nutrition preparations. Provide the body with plastic and energy material, bypassing the gastrointestinal tract. This group includes protein hydrolysates (amino acids with peptides, mineral salts, and dextrose), amino acid solutions (polyamine), fat emulsions, and sugars.
- Regulators of acid-base and water-electrolyte balance. Used for homeostasis correction. Include buffer (trometamol, sodium bicarbonate) and saline solutions (isotonic solution, Ringer's solution).
- Oxygen carriers. A unique group of preparations capable of transporting blood gases (perftoran, perfukal).
Briefly: answers to topical questions
What are the contraindications to the intravenous administration of hemodynamic blood substitutes?
Contraindications to the intravenous administration of hemodynamic blood substitutes depend on the specific preparation and include kidney pathologies, trauma, and bleeding. These include:
- Acute and chronic nephritis — is a relative contraindication.
- Chronic kidney disease — a contraindication for the use of low-molecular-weight dextrans.
- Traumatic brain injury — a contraindication for medium-molecular-weight dextrans.
- Increased intracranial pressure.
- Ongoing internal bleeding.
Which specific preparations are included in the group of detoxification blood substitutes?
The group of detoxification blood substitutes includes various solutions based on polyvinyl alcohol, povidone, and dextrans used to relieve intoxication. Specific representatives include:
- Low-molecular-weight polyvinyl alcohol.
- Povidone + saline components (sodium, potassium, calcium, magnesium chlorides, and sodium bicarbonate).
- Polyglukin.
- Rheopolyglucin.
- Hemodez.
What complications can occur with massive infusion of blood-substituting liquids?
With massive infusion of blood-substituting liquids, severe complications may develop associated with vascular bed volume overload and reactions to the preparation. Possible complications:
- Hypervolemia — can lead to the development of heart failure.
- Pulmonary edema — occurs due to intravenous fluid overload (non-cardiogenic edema) or as a result of a decrease in colloid-osmotic pressure (during crystalloid transfusion).
- Infusion reactions — include individual hypersensitivity (for example, during dextran infusion).
Through which physicochemical processes is the mechanism of action of detoxification blood substitutes realized?
The mechanism of action of detoxification blood substitutes is realized through hemodilution, toxin binding, the release of tissue toxins into the blood, and their excretion by the kidneys. Main processes:
- Hemodilution — dilution of blood, leading to a decrease in the concentration of circulating toxins.
- Release of tissue toxins into the blood followed by removal by the kidneys.
- Toxin binding.
- Excretion — elimination of excess fluid and toxins through the kidneys, which is facilitated by an increase in diuresis.
For quick memorization of groups by action, use the phrase: "Hemodynamic, Detoxification, Nutrition (parenteral), Regulators (water-electrolyte), Oxygen carriers".
Class and exam questions
Can all blood be replaced by a single product?
No. A blood-substituting fluid replaces only a specific function of blood (e.g., volume or nutrition). For a comprehensive effect, it is necessary to administer mixtures or use products sequentially.
What happens to the solution after it has performed its function?
According to basic requirements, a quality preparation must be completely metabolized by the enzymes of the patient's body or excreted unchanged.
Why are standard colloids not used for parenteral nutrition?
Colloid solutions (dextrans, gelatins) perform a hemodynamic function. Nutrition requires building blocks and energy — amino acids, protein hydrolysates, fat emulsions, and sugars.
What else to study on this topic
- Mechanism of action of low-molecular-weight dextrans in hemorrhagic shock
- Specifics of using Perftoran as an oxygen carrier
- Principles of calculating parenteral nutrition mixture composition
- Correction of acid-base balance with buffer solutions
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