Types of Plasma Substituents

Plasma substituents, also known as plasma expanders, are fluids that can be infused into a patient's bloodstream to increase the plasma volume. These are often used in medical situations where there is blood loss or a reduction in blood volume (hypovolemia), such as trauma, surgery, or severe burns. Plasma substituents help maintain adequate blood pressure, improve circulation, and ensure that vital organs receive sufficient oxygen and nutrients.

Types of Plasma Substituents

Plasma expanders can be broadly classified into two categories:

1. Crystalloids

Crystalloids are solutions of small molecules that can easily pass through the blood vessel walls into tissues. They are typically composed of water with electrolytes, such as sodium and chloride, and can rapidly expand the intravascular volume.

• Examples:

  • Normal saline (0.9% sodium chloride): A commonly used isotonic solution.
  • Ringer's lactate: Contains electrolytes like sodium, potassium, calcium, and lactate, and is often used in cases of trauma or surgery.
  • Dextrose 5% in water (D5W): A hypotonic solution that provides free water and a small amount of glucose.

• Advantages: Crystalloids are inexpensive and widely available.

• Disadvantages: Large volumes may be required to achieve adequate plasma expansion, which can lead to edema (fluid accumulation in tissues).

2. Colloids

Colloids are solutions containing larger molecules, such as proteins or synthetic polymers, which stay in the blood vessels longer than crystalloids and are more effective at expanding plasma volume. They exert oncotic pressure, drawing fluid from the tissues into the bloodstream.

• Types of colloids:

  • Natural colloids:
    • Albumin: A natural protein found in blood plasma. Albumin solutions are often used in critical care to restore blood volume, especially in cases of hypoalbuminemia (low blood albumin levels).
    • Plasma: Fresh frozen plasma (FFP) is a natural source of clotting factors, albumin, and immunoglobulins, used in specific situations like coagulopathy (bleeding disorders).
  • Synthetic colloids:
    • Hydroxyethyl starch (HES): A synthetic polymer used to increase plasma volume in trauma and surgical patients.
    • Gelatins: Solutions derived from bovine collagen, used as a plasma expander.
    • Dextrans: Polysaccharide solutions that act as plasma volume expanders by maintaining blood pressure.

• Advantages: Colloids are more efficient at increasing blood volume with smaller quantities compared to crystalloids.

• Disadvantages: They are more expensive and can have side effects, such as allergic reactions, coagulopathy (blood clotting issues), and kidney damage, especially with synthetic colloids like HES.

Key Differences Between Crystalloids and Colloids:

• Crystalloids: Quickly diffuse into tissues, requiring larger volumes for plasma expansion.
• Colloids: Stay in the circulation longer, providing sustained volume expansion with smaller amounts, but have higher risks and costs.

In summary, plasma substituents play a crucial role in managing hypovolemia and shock, and the choice between crystalloids and colloids depends on the clinical situation, patient needs, and risks associated with the fluids.