Sources of plastic material
To restore the nutritional function of blood, protein hydrolysates and amino acid mixtures are used. It is important to remember the basic physiological law: the whole protein molecule is not broken down in the liver. This is precisely why whole blood, plasma, and serum are used solely for hemocorrection rather than as a nutrient medium.
- Protein hydrolysates. They consist of dispensable and indispensable amino acids as well as low-molecular-weight peptides (which are ultimately broken down in the liver). The raw materials for their production are technical casein, unused donor blood, and placental blood. The assimilation of nitrogen from them reaches 80–93%.
- Amino acid mixtures. These are balanced solutions of chemically pure crystalline amino acids (e.g., Polyamine, Aminofusin, Moriamin, Vamin). Polyamine contains 8 essential amino acids and D-sorbitol, and is stored at temperatures from $-10$ to $+20^\circ\text{C}$ for two years.
Dosage of protein products:
| Type of nutrition | Protein hydrolysates | Amino acid mixtures |
|---|---|---|
| Total | $1500–2000$ mL/day | $800–1200$ mL/day |
| Partial | $700–1000$ mL/day | $400–600$ mL/day |
Energy components: carbohydrates and alcohols
Sugars and polyhydric alcohols meet the body's energy demands, which directly contributes to the accumulation of endogenous proteins. The baseline daily dose is 250 g/day.
- Dextrose (5%, 10%, 20%, and 40% solutions). It is rarely used on its own, primarily acting as an energy supplement to protein hydrolysates. Its excess is rapidly excreted by the kidneys.
- Fructose and Sorbitol (polyhydric alcohol). These are the drugs of choice when glucose assimilation is impaired due to stress, shock, or diabetes mellitus. Their key advantage is that their assimilation does not depend on insulin. Both substances are broken down in the liver. Sorbitol is typically used as a 5% solution.
Fat emulsions
Fats are prescribed for prolonged parenteral nutrition (3–4 weeks) or when it is necessary to administer a massive amount of calories in a strictly limited fluid volume.
- Composition: soybean oil and triglycerides (20% emulsion). Particle size does not exceed 1 µm.
- Energy density: 2100 kcal/L.
The use of fat emulsions is strictly contraindicated in the early postoperative period, in shock, severe liver disease, uncompensated diabetes mellitus, severe atherosclerosis, and when there is a risk of fat embolism or thrombophlebitis.
Indications and contraindications for protein nutrition
Protein-based blood substitutes are intended to correct hypo- and dysproteinemia.
Main indications:
- Preparation for surgery in malnourished and wasted patients.
- Pathologies with severe protein loss: oncological diseases, peptic ulcer disease, esophageal stenosis, or gastric antral stenosis.
- Purulent-inflammatory processes (peritonitis, pleural empyema, lung abscess, extensive phlegmons).
- Postoperative period (especially gastrointestinal surgery) to maintain nitrogen balance and wound healing.
- Burn disease, osteomyelitis, and intestinal obstruction (due to massive protein breakdown and loss via exudate or pus).
Contraindications: Acute circulatory disorders (shock, acute blood loss), acute and subacute renal failure, thrombosis and thromboembolism. The primary route of administration is intravenous; less commonly, they are administered intraoperatively via a small bowel tube.
Briefly: answers to topical questions
What complications can arise from prolonged parenteral nutrition?
The provided sources indicate the following potential problems related to nutrition components during parenteral nutrition:
- Ketosis — with isolated use of fat emulsions; fat emulsions must be combined with carbohydrates.
- Fluid overload (hyperhydration) — risk when administering large volumes of isotonic dextrose solution.
- Plasma hyperosmolarity — hazard when using highly concentrated dextrose solutions.
Is the administration of hyperosmolar solutions for parenteral nutrition permitted in central or peripheral veins?
The cited sources do not explicitly state whether hyperosmolar solutions for parenteral nutrition are permitted in central or peripheral veins.
Only the following is confirmed:
- central venous catheterization is indicated when parenteral nutrition, massive infusion therapy is required, and when peripheral venous access is limited;
- highly concentrated dextrose solutions pose a risk of developing plasma hyperosmolarity.
The "whole molecule" rule: whole blood and plasma are not broken down in the liver, so they are infused solely for hemocorrection, whereas exclusively hydrolysates and amino acids are used for nutrition.
Class and exam questions
Why is regular dextrose not always suitable in diabetes mellitus or shock?
Glucose assimilation is impaired in these conditions. In such cases, fructose and sorbitol become the drugs of choice, as their hepatic metabolism does not depend on insulin production.
Can a protein hydrolysate be used if a precipitate has formed in the vial?
A light precipitate is acceptable if it completely disappears upon shaking. However, if the precipitate is persistent or cloudiness appears, the product must categorically not be used.
What happens if a single essential amino acid is missing from an amino acid mixture?
According to the law of protein synthesis, if even a single essential amino acid is missing from the incoming complex, the synthesis of endogenous protein in the body will not occur.
What else to study on this topic
- Composition and electrolyte balance of combined hydrolysates with dextrose.
- Peculiarities of protein dosage calculation in extensive burns and peritonitis.
- Methodology of intraoperative enteral tube feeding.
- Symptoms and prevention of fat embolism during the infusion of fat emulsions.
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Other topics of "CHAPTER 7. BLOOD SUBSTITUTES"
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