Plasma Expanders

PLASMA EXPANDERS

Introduction:

• High molecular weight substances.

Desirable properties of plasma expander:

• Should exert oncotic pressure comparable to plasma.
• Should remain in circulation and not leak out in tissues, or be too rapidly disposed of.
• Should be pharmacodynamically inert.
• Should not be pyrogenic or antigenic.
• Should not interfere with grouping and cross-matching of blood.
• Should be stable, easily sterilizable & cheap.

Uses:

• Primarily as plasma substitutes – 
  • Mainly in conditions where plasma is lost or moved to extravascular compartment.
  • E.g. in burns (acute phase only), hypovolemic, endotoxin shock, severe trauma & extensive tissue damage.

Contraindications:

• Severe anemia
• Heart failure
• Pulmonary edema
• Liver & kidney failure.

Substances used as plasma expanders:

• Albumin, Dextran, Polygeline & Hetastarch.

Individual substances:

1. Albumin:

• Does not interfere with blood grouping or coagulation.
• Free of hepatitis transmission risk (as it is heat treated).
• Highly expensive.

Uses:

• In hypovolemia
• Burns
• Shock
• Hypoalbuminemia.

2. Dextran:

• Most commonly used plasma expanders.
• Interferes with blood grouping, coagulation & platelet function.
• Reduces blood viscosity.
• Decreases rouleau formation.
• Improves microcirculation.

Dextran-70:

• Longer-acting (24 hours)

Dextran-40:

• Rapid but short-acting.
• Has thromboprophylactic (anti-thrombotic) effect.
• Provides temporary improvement in patient’s ischaemic foot through intravenously.

3. Polygeline:

• Degraded gelatin polymer.
• Polypeptide with average MW 30,000.
• Exerts oncotic pressure similar to albumin.
• Not antigenic.
• More expensive than dextran.

Uses: For priming of heart-lung & dialysis machines.

Adverse effects: Hypersensitivity reactions like flushing, rigor, urticaria, wheezing & hypotension.

4. Hetastarch:

• Complex mixture of ethoxylated amylopectin of various molecular sizes.
  • Average MW 4.5 lac (range 10,000 to 1 million).
  • Smaller molecules (MW < 50,000) are excreted renaly.
  • Larger molecules are slowly broken down to smaller ones.
• Incompatible with many drugs 
• Non-injectable drug is added to infusion.
  • Plasma volume expands slightly in excess of infused volume.
• Colloidal properties of 6% hetastarch approximate human albumin.
• Blood grouping & cross matching may be vitiated.

Uses:

• Used to improve harvesting of granulocytes – As it accelerates erythrocyte sedimentation.
• Hemodynamic status improved for 24hrs or more.

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