Plasma expanders, also known as volume expanders, are intravenous fluids that increase the circulating volume or plasma volume in a person's body. They are used to treat hypovolemia or low blood volume caused by conditions like hemorrhage, dehydration, diarrhea or burns. By increasing intravascular volume, volume expanders can help improve blood flow and oxygen delivery to vital organs.

Types of Plasma Expanders
There are different types of volume expanders used in clinical practice depending on the situation:

Crystalloids
Crystalloids include normal saline and lactated ringer's solution. They are cheap and readily available fluid options that expand extracellular fluid volume when administered intravenously. However, their effects are short-lived as they distribute throughout the extracellular space and are easily replaced. Large volumes may be required for adequate volume repletion.

Colloids
Colloid solutions contain larger molecules that remain in the vascular space for longer and are more effective plasma volume expanders. Examples include:

- Dextrans: Derived from sucrose, dextrans come in various molecular weights. They increase circulating blood volume and plasma oncotic pressure. However, anaphylactoid reactions are a risk.

- Hydroxyethyl starches (HES): Synthetic starches that are effective plasma volume expanders. Newer generations carry a lower risk of adverse effects.

- Gelatins: Colloid alternatives derived from bovine collagen. They are cheaper than HES but less effective volume expanders. Associations with kidney injury are controversial.

- Albumin: Human serum albumin purified from donor blood. It expands intravascular volume well but is expensive and in short supply.

Workings

Plasma expanders work by increasing intravascular oncotic pressure through their presence in circulating blood. This counters the effects of low oncotic pressure seen in conditions like bleeding or dehydration, where fluid and proteins have been lost from the bloodstream.

By drawing fluid back into blood vessels, volume expanders augment circulating blood volume and subsequently improve cardiac preload and cardiac output. This helps restore tissue perfusion pressure and oxygen delivery to vital organs supported by increased blood flow.

Clinical Uses of Plasma Expanders
Volume expanders find several applications in clinical practice:

Trauma and Hemorrhagic Shock
In major bleeding from traumatic injuries, volume expanders like crystalloids and colloids are widely used as initial fluid resuscitants. They help stabilize the patient until bleeding is controlled through surgery or other means.

Burn Injuries
Patients with extensive burns suffer significant fluid loss through damaged skin and increased vascular permeability. Volume expanders play a vital role in volume expansion and restoration of effective circulation in burn shock.

Pre-operative Optimization
In high risk surgical cases, volume expanders preload the circulation and optimize hemodynamic status prior to procedures to reduce complications from blood loss or hypovolemia during surgery.

Renal Dialysis
Patients on hemodialysis often require volume expansion with plasma substitutes before, during or after dialysis sessions to prevent intradialytic hypotension from rapid fluid removal.

Dengue and other Bleeding Diatheses
Conditions associated with internal bleeding and leakage of fluids from blood vessels are effectively managed with volume expansion using crystalloids and colloids to compensate for fluid losses.

Adverse effects and Risks
While volume expanders are largely safe when used judiciously, certain risks and adverse effects must be considered:

- Allergic reactions: Rare but potentially life-threatening anaphylactic reactions have been reported especially with dextran and gelatin containing products.

- Coagulation abnormalities: Large volumes of certain colloids may disturb clotting and bleeding times by interacting with coagulation factors.

- Acute kidney injury: Some studies link hydroxyethyl starch to an increased risk of renal impairment especially in critical care patients with sepsis. Newer generations seem safer.

- Cost implications: While crystalloids are cheap, frequent large volume use can add up. Albumin and newer colloids are much more expensive options.

- Fluid overload: Overenthusiastic volume expansion therapy without addressing the underlying cause can precipitate or worsen pulmonary or peripheral edema in susceptible patients. Close monitoring of fluid balance is important.

Thus in summary, volume expanders play an indispensable role in initial fluid resuscitation and management of conditions involving fluid and volume depletion. But their uses require a detailed understanding of indications, pharmacokinetics and potential adverse effects for safe clinical application. Combined with addressing the underlying disease process, plasma expanders can help optimize hemodynamics and organ perfusion in various critical illnesses.

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