Mechanism and essence of the method
Surgical intervention is often associated with the risk of bleeding. The use of hemodilution minimizes harm to the body. The essence is that a state is artificially created in the vascular bed where the concentration of cellular (formed) elements and various plasma factors is temporarily reduced.
As a result, when bleeding occurs during surgery, the patient loses not whole blood, but an already diluted mixture. This preserves the patient's own red blood cells and clotting factors, which are critical for normal recovery in the postoperative period.
Acute normovemic hemodilution
This type of blood dilution involves the mandatory exfusion (collection) of the patient's own blood. The procedure is performed strictly immediately before surgery.
How it works:
- A specific volume of blood is collected (exfused) from a vein. The blood is collected into special vials containing a preservative.
- Simultaneously with blood collection, a hemodiluent—a multicomponent replacement solution—is administered intravenously.
- The collected autologous blood is stored throughout the surgical intervention.
- At the end of the surgery, this autologous blood is mandatorily reinfused (returned) to the patient.
Composition of the administered hemodiluent:
- Dextran with a medium molecular weight from 30,000 to 40,000.
- 20% albumin solution.
- Ringer-Locke solution.
Calculation of volumes in normovolemic hemodilution
The volume of blood withdrawn and solutions administered directly depends on the required degree of blood dilution. The target parameter is the hematocrit level. The volume of administered fluid must always exceed the volume of withdrawn blood to maintain adequate hemodynamics.
| Parameter | Moderate hemodilution | Significant hemodilution |
|---|---|---|
| Decrease in hematocrit | by 1/4 | by 1/3 |
| Volume of exfusion (withdrawal) | 800 ml | 1200 ml |
| Total volume of hemodiluent | 1100–1200 ml | 1600 ml |
| — Dextran (30,000–40,000) | 400 ml | 700 ml |
| — Ringer-Locke solution | 500–600 ml | 750 ml |
| — 20% albumin solution | 100 ml | 150 ml |
Hypervolemic hemodilution
An alternative approach is hypervolemic hemodilution, which is performed without blood exfusion (withdrawal). Like the normovolemic variant, it is used preoperatively to prevent and reduce blood loss volumes.
Essence of the method: The patient is intravenously administered infusion media without any prior extraction of their own blood. The primary focus is on using solutions with pronounced colloidal properties.
Such agents are able to effectively remain retained within the vascular bed. These include:
- Albumin;
- Dextran with a higher average molecular weight ranging from 50,000 to 70,000.
Expected effect: Since no blood is extracted and the fluid volume within the vessels increases due to colloids, a predictable increase in circulating blood volume (CBV) occurs. Against the background of increased CBV, blood dilution takes place, which again ensures that only diluted blood is lost in the event of intraoperative bleeding.
Briefly: answers to topical questions
What target hematocrit and hemoglobin levels are permitted during hemodilution?
During hemodilution, a reduction in hematocrit by a certain fraction of the initial value is permitted, although precise absolute target figures for hemoglobin and hematocrit are not defined. The degree of dilution depends on the type of procedure performed:
| Parameter | Moderate hemodilution | Significant hemodilution |
|---|---|---|
| Decrease in hematocrit | by 1/4 | by 1/3 |
Which specific preservative solutions are used to preserve the collected autologous blood during normovolemic hemodilution?
To preserve the collected autologous blood during acute normovolemic hemodilution, exfusion is performed into vials containing a preservative. In general, solutions containing a stabilizer (sodium citrate) and a preservative (dextrose, sucrose) are used for blood preservation. Specific names of such solutions include:
- "Glugicir" — ensures a storage period of up to 21 days.
- "Ciglufad" — allows blood to be stored for up to 35 days.
Remember the difference: Normovolemic — "withdrawn into a bag and replaced with solution" (with exfusion). Hypervolemic — "colloids simply added on top of the baseline" (without exfusion, CBV increases).
Class and exam questions
When is the blood collected during normovolemic hemodilution returned to the patient?
The autologous blood collected in preservative vials is returned (reinfused) to the patient strictly at the end of the operation.
What is the main difference between hypervolemic and acute normovolemic hemodilution?
Hypervolemic hemodilution is performed by administering colloidal solutions without prior blood exfusion (withdrawal), which leads to an increase in CBV.
Which dextrans are used in different types of blood dilution?
In normovolemic hemodilution, the hemodiluent contains dextran with a molecular weight of 30,000–40,000, whereas in hypervolemic hemodilution, dextran with a molecular weight of 50,000–70,000 is used.
What else to study on this topic
- Indications and contraindications for acute normovolemic hemodilution
- Mechanisms of action of dextrans with different molecular weights
- Complications associated with inadequate calculation of infusion media
- Monitoring of vital functions during exfusion and autologous blood reinfusion
Master the entire topic in the "General Surgery" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Hemodilution" and 3,335 other topics in the subject
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 70 video lessons on the subject
Other topics in the section "CHAPTER 6. BLOOD TRANSFUSION"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.