Plasma Expanders

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Chapter: Essential pharmacology : Hypolipidaemic Drugs And Plasma Expanders

These are high molecular weight substances which exert colloidal osmotic (oncotic) pressure, and when infused i.v. retain fluid in the vascular compartment. They are used to correct hypovolemia due to loss of plasma/blood.


PLASMA EXPANDERS

 

These are high molecular weight substances which exert colloidal osmotic (oncotic) pressure, and when infused i.v. retain fluid in the vascular compartment. They are used to correct hypovolemia due to loss of plasma/blood.

 

Human plasma or reconstituted human albumin would seem to be the best. However, the former carries risk of transmitting serum hepatitis, AIDS, etc., and the latter is expensive. Therefore, synthetic colloids are more often used.

 

Desirable Properties Of A Plasma Expander Are:

 

·            Should exert oncotic pressure comparable to plasma.

·            Should remain in circulation and not leak out in tissues, or be too rapidly disposed.

·            Should be pharmacodynamically inert.

·            Should not be pyrogenic or antigenic.

·            Should not interfere with grouping and crossmatching of blood.

·            Should be stable, easily sterilizable and cheap.

 

Substances Employed Are:

 

Human Albumin

Hydroxyethyl starch

Dextran                

(HES); (Hetastarch)

Degraded gelatin Polyvinyl pyrrolidone - (PVP)

Polymer

 

Human  Albumin                                                                       

 

It is obtained from pooled human plasma; 100 ml of 20% human albumin solution is the osmotic equivalent of about 400 ml of fresh frozen plasma or 800 ml of whole blood. It can be used without regard to patient’s blood group and does not interfere with coagulation. Unlike whole blood or plasma, it is free of risk of transmitting serum hepatitis because the preparation is heat treated. There is also no risk of sensitization with repeated infusions.

 

The 20% solution draws and holds additional fluid from tissues: crystalloid solutions must be infused concurrently for optimum benefit. Apart from burns, hypovolemia, shock, etc., it has been used in acute hypoproteinaemia, acute liver failure and dialysis. Dilution of blood using albumin and crystalloid solutions can be used before cardiopulmonary bypass. Febrile reaction to human albumin occurs occasionally. It is expensive.

 

Human albumin 20%: ALBUDAC, ALBUPAN 50, 100 ml inj., ALBUMED 5%, 20% infusion (100 ml)

 

Dextran

 

It is a polysaccharide obtained from sugar beat which is available in two forms.

 

Dextran70 (MW 70,000): DEXTRAN70, LOMODEX70; 6% solution in dextrose or saline, 540 ml vac. Dextran40 (MW 40,000; low MW dextran): LOMODEX 10% solution in dextrose or saline, 540 ml vac.

 

The more commonly used preparation is dextran70. It expands plasma volume for nearly 24 hours, and is slowly excreted by glomerular filtration as well as oxidized in the body over weeks. Some amount is deposited in RE cells. Dextran has nearly all the properties of an ideal plasma expander except:

 

a)     It may interfere with blood grouping and crossmatching.

b)  Though the dextran used clinically is not antigenic, its structure is similar to other antigenic polysaccharides. Some polysaccharide reacting antibodies, if present, may cross react with dextran and trigger anaphylactic reaction. Urticaria, itching, bronchospasm, fall in BP occur occasionally; anaphylactic shock is rare.

c)    It can interfere with coagulation and platelet function and thus prolong bleeding time; should not be used in hypofibrinogenaemia, thrombocytopenia or in presence of bleeding.

 

Dextran-40

It acts more rapidly than dextran70. It reduces blood viscosity and prevents RBC sludging that occurs in shock by coating them and maintaining their electronegative charge. Microcirculation may improve. However, it is rapidly filtered at the glomerulus: expands plasma volume for a shorter period, and may get highly concentrated in the tubule if oliguria develops—tubular obstruction may occur. The total dose should not exceed 20 ml/kg in 24 hr. It has also been tried in stroke and for prophylaxis of deep vein thrombosis and pulmonary infarction.

 

Dextrans can be stored for 10 years and are cheap.

They are the most commonly used plasma expanders.

 

Degraded Gelatin Polymer (Polygeline)

 

It is a polypeptide with average MW 30,000 which exerts oncotic pressure similar to albumin and is not antigenic; hypersensitivity reactions are rare, but should be watched for. It does not interfere with grouping and crossmatching of blood and remains stable for three years. It is not metabolized in the body; excreted slowly by the kidney. Expansion of plasma volume lasts for 12 hours. It is more expensive than dextran. It can also be used for priming of heartlung and dialysis machines.

 

Hypersensitivity reactions like flushing, rigor, urticaria, wheezing and hypotension can occur. HAEMACCEL,SERACCEL 500 ml vac. (as 3.5% solution in balanced electrolyte medium).

 

Hydroxyethyl Starch (HES; Hetastarch)

 

It is a complex mixture of ethoxylated amylopectin of various molecular sizes; average MW 4.5 lac (range 10,000 to 1 million). The colloidal properties of 6% HES approximate those of human albumin. Plasma volume expands slightly in excess of the volume infused. Haemodynamic status is improved for 24 hour or more.

 

Smaller molecules (MW < 50,000) are excreted rapidly by kidney; 40% of infused dose appears in urine in 24 hr. Larger molecules are slowly broken down to smaller ones and eliminated with a t½ of 17 days.

 

Adverse effects are vomiting, mild fever, itching, chills, flu like symptoms, swelling of salivary glands. Urticaria, periorbital edema and bronchospasm are the anaphylactoid reactions.

 

It has also been used to improve harvesting of granulocytes because it accelerates erythrocyte sedimentation. EXPAN 6% inj (100, 500 ml vac)

 

Polyvinylpyrrolidone (PVP)

 

It is a synthetic polymer (average MW 40,000) used as a 3.5% solution. It interferes with blood grouping and crossmatching and is a histamine releaser. PVP is slowly excreted by kidney and small amounts by liver into bile. A fraction is stored in

RE cells for prolonged periods. It has been found to bind penicillin and insulin in circulation so that the same is not available for action. It is infrequently used as a plasma expander.

 

OSMOPLASMA, SIOPLASMA; 3.5% solution in buffered normal saline, 540 ml vac.

 

Use Of Plasma Expanders

 

These colloidal solutions are used primarily as substitutes for plasma in conditions where plasma has been lost or has moved to extravascular compartment, e.g. in burns, hypovolemic and endotoxin shock, severe trauma and extensive tissue damage. They can also be used as a temporary measure in cases of whole blood loss till the same can be arranged: but they do not have O2 carrying capacity.

 

Contraindications to plasma expanders are— severe anaemia, cardiac failure, pulmonary edema, renal insufficiency.

 


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