Mechanism of action and classification
Hemodynamic agents are divided into two functional groups:
- Medium-molecular-weight blood substitutes (hemodilutants). Their main task is hemodilution and maintenance of CBV. They circulate in the vascular bed for a prolonged period, effectively drawing in interstitial fluid. This leads to a sustained restoration of blood pressure. The main indications are shock and acute blood loss.
- Low-molecular-weight blood substitutes. Their profile is rheology improvement and detoxification. They restore capillary perfusion, remove excess fluid with toxins, and are excreted faster by the kidneys. They are prescribed for dehydration, intoxications, and microcirculation disorders.
Dextran preparations
Dextran (Dextranum) is a dextrose polymer of bacterial origin. In surgery, its solutions in isotonic sodium chloride are used (solution pH 4.5–6.5). The preparation is produced sterile in 400 ml bottles, and its shelf life reaches 5 years. Storage is permitted at temperatures from -10 °C to +20 °C (after thawing, therapeutic properties are fully restored).
- Medium-molecular-weight dextran (avg. molecular weight 50,000–70,000, 6% solution).
Its molecular weight is close to that of albumin, which is ideal for maintaining normal colloid-osmotic pressure.
- Hemodynamics: Surpasses other blood substitutes. Increases plasma volume more than the administered volume of the drug. Restores blood pressure (BP) and central venous pressure (CVP). Circulates for 3–4 days (half-life is 1 day).
- Detoxification: Contains up to 20% low-molecular-weight fractions, which increase diuresis and promote the transfer of tissue toxins into the blood for renal elimination.
- Indications: Traumatic, burn, and operative shock; acute blood loss; sepsis, peritonitis, intestinal obstruction; exchange transfusions.
- Administration: Single dose from 400 to 1,200 ml (sometimes up to 2,000 ml). In emergency care, start with rapid IV infusion (jet), and as BP rises, switch to drip infusion (60–70 drops/min).
- Contraindications: Traumatic brain injury, high intracranial pressure, ongoing internal bleeding.
- Low-molecular-weight dextran (avg. molecular weight 30,000–40,000, 10% solution).
- Volumic effect: Every 20 ml of the solution additionally binds 10–15 ml of tissue water.
- Rheology: Exerts a potent disaggregating effect on erythrocytes, eliminates stasis, reduces blood viscosity, and produces a strong diuretic effect (useful in intoxications).
- Elimination: Leaves the vascular bed within 2–3 days, but the bulk is excreted in the urine within the first 24 hours.
- Specific indications: Prevention and treatment of thromboembolic disease, post-transfusion complications, prevention of acute renal failure (ARF).
- Limitations: Contraindicated in chronic kidney disease. The average dosage is 500–750 ml.
Gelatin preparations
This group includes an 8% solution of partially hydrolyzed gelatin (Gelatinum) with a relative molecular weight of 20,000–25,000 in an isotonic NaCl solution.
- Properties: Increases CBV due to colloidal characteristics. However, its main effect is rheological: the drug dilutes the blood, reduces its viscosity, and improves microcirculation. The solution has no nutritional value.
- Pharmacokinetics: Unlike dextrans, gelatin leaves the vascular bed extremely quickly. Only 2 hours later, merely 20% of the administered dose remains in the vessels. It is completely excreted in the urine within 24 hours.
- Application: Administered intravenously (jet or drip) and intra-arterially. The solution is actively used to prime heart-lung machines (cardiopulmonary bypass).
Briefly: answers to topical questions
Which specific drugs (trade names) belong to medium-molecular-weight dextrans?
Medium-molecular-weight dextrans include Polyglukin. This is a colloidal solution with an average molecular weight of 50,000–70,000, used as a blood-substituting fluid with hemodynamic action. The drug circulates in the vascular bed for a prolonged period, draws in interstitial fluid, and effectively restores circulating blood volume in shock or acute blood loss.
Which specific drugs (trade names) belong to low-molecular-weight dextrans?
Low-molecular-weight dextrans include Rheopolyglucin. It is a colloidal dextran solution with an average molecular weight of 30,000–40,000. This hemocorrective agent is used to improve microcirculation, disaggregate erythrocytes, reduce blood viscosity, and replenish circulating blood volume in capillary perfusion disorders and intoxications.
What are the contraindications for the administration of medium-molecular-weight dextran?
Contraindications for the administration of medium-molecular-weight dextran are:
- traumatic brain injury;
- increased intracranial pressure;
- ongoing internal bleeding.
What are the indications for the use of gelatin preparations in surgical practice?
In surgical practice, gelatin preparations are used in the following cases:
- an 8% solution of partially hydrolyzed gelatin is used to prime the heart-lung machine (cardiopulmonary bypass);
- hemostatic gelatin sponge is used for capillary and parenchymal hemorrhage from bones, muscles, and parenchymal organs, as well as for the tamponade of dural venous sinuses;
- in Shkolnikov-Selivanov intrapelvic block, gelatinol is mixed with a procaine solution to prolong the effect.
Remember the difference between dextrans using the rule "M/L": Medium-molecular (Srednemoлекулярные) — Maintain pressure and Stay in the vascular bed for a long time (3–4 days). Low-molecular (Nizkomolekulyarnyye) — Normalize microcirculation and Immediately excrete (within 1 day).
Class and exam questions
Why should medium-molecular-weight dextran not be administered during ongoing bleeding?
The drug is a potent hemodiluent. It rapidly draws fluid into the vessels and raises blood pressure, which can dislodge a blood clot and increase internal bleeding.
How can plasma volume after dextran infusion exceed the volume of the administered drug?
Dextran molecules have a high osmotic potential: they actively attract water from the interstitial space into the vascular bed. For example, every 20 ml of low-molecular-weight dextran binds an additional 10–15 ml of water.
Can a frozen solution of medium-molecular-weight dextran be used?
Yes, the drug can be stored at temperatures down to -10 °C. After natural thawing, its therapeutic physicochemical properties are fully restored.
What else to study on this topic
- Calculation of dosage and infusion rate depending on the severity of shock
- Mechanisms of colloid-osmotic pressure in the vascular bed
- Use of gelatin preparations in heart-lung machines (cardiopulmonary bypass)
- The role of low-molecular-weight fractions in the prevention of acute renal failure (ARF)
- Management of post-transfusion complications using hemodilutants
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