Saidala 24: Plasma expanders

Definition and Clinical Use

Plasma expanders are a pharmacological and clinical class of intravenous (IV) fluids used to increase or restore intravascular volume in patients experiencing hypovolemia, hypotension, or shock. Unlike crystalloids (e.g., saline, Ringer’s lactate), which distribute throughout the extracellular space, plasma expanders contain large molecules (colloids) that remain within the vascular compartment, creating oncotic pressure that pulls or retains fluid in the bloodstream.

They are used in a variety of clinical scenarios, including trauma, burns, hemorrhage, sepsis, and perioperative fluid management. However, their use is controversial, with varying safety and efficacy profiles across products.

1. Classification of Plasma Expanders

Plasma expanders are classified into two broad types based on their composition:

A. Natural Colloid Solutions

Human Albumin Solutions (HAS)
- Albumin 5% (iso-oncotic): volume expander
- Albumin 20–25% (hyperoncotic): draws interstitial fluid into vasculature
Plasma Protein Fraction (PPF)
- A mix of albumin and other plasma proteins; less commonly used than pure albumin

B. Synthetic Colloid Solutions

Hydroxyethyl Starch (HES)
- Examples: Hetastarch, Voluven, Volulyte
- Vary by molecular weight (MW) and degree of substitution
Dextrans
- Dextran 40 (low MW): improves microcirculation
- Dextran 70 (higher MW): used for volume expansion
Gelatins
- Examples: Polygeline, Succinylated gelatin, Urokinase-based gelatins
- Derived from bovine collagen; less commonly used globally

2. Mechanism of Action

Plasma expanders act primarily through colloid osmotic pressure (also known as oncotic pressure):

The large molecules in these fluids cannot pass easily through capillary membranes.
This leads to an increase in intravascular oncotic pressure, which:
- Retains existing plasma water
- Draws additional fluid from the interstitial and intracellular compartments
The net effect is plasma volume expansion and hemodynamic stabilization

3. Indications

Plasma expanders are indicated in various acute care and surgical settings where rapid intravascular volume repletion is essential:

A. Hypovolemic Shock

Due to blood loss, trauma, burns, or dehydration

B. Hypoproteinemia

Albumin solutions are used in hypoalbuminemic patients (e.g., nephrotic syndrome, liver cirrhosis)

C. Burns

Used in intermediate to late resuscitation phases to maintain intravascular volume

D. Sepsis and Septic Shock

Historically used in septic patients, though recent evidence supports cautious or limited use

E. Hemodialysis

To prevent hypotension during or after dialysis

F. Cardiopulmonary Bypass Surgery

Used during priming of bypass machines to maintain circulatory volume

G. Toxin or Drug Removal (Dextrans)

Facilitate renal excretion of nephrotoxic substances in select cases

4. Generic Drug Names and Products

Generic Name	Brand Examples	Type
Albumin (Human)	Albutein, AlbuRx, Albuminar	Natural colloid
Dextran 40	Rheomacrodex	Synthetic colloid (low MW)
Dextran 70	Macrodex	Synthetic colloid (high MW)
Hetastarch	Hextend, Hespan	HES (6%, 10%)
Hydroxyethyl Starch	Voluven, Volulyte	HES (varied MW)
Gelatin (Polygeline)	Haemaccel, Gelofusine	Gelatin-based

5. Pharmacokinetics

Agent	Half-Life	Excretion	Volume Expansion Effect
Albumin 5%	~16 hours	Renal + catabolism	1:1 plasma volume expansion
Albumin 20–25%	>16 hours	Renal + catabolism	Expands plasma volume >1:1
Dextran 40	2–4 hours	Renal (filtration)	Moderate volume expander
Dextran 70	6–12 hours	Renal	Stronger volume expansion
HES 130/0.4	~12 hours	Renal + RES	Effective; less coagulopathy
Gelatins	2–4 hours	Renal	Short-lived expansion

Note: Larger molecules tend to stay longer in the circulation but are associated with higher toxicity.

6. Adverse Effects

General:

Volume overload, especially in patients with heart failure or renal dysfunction
Allergic or anaphylactoid reactions, especially with dextrans and gelatins
Dilutional coagulopathy from excessive volume replacement

Specific to Agents:

Albumin:

Rare allergic reactions
Fluid overload (especially 25% solutions)

Dextrans:

Anaphylaxis
Platelet dysfunction
Interfere with blood crossmatching

HES:

Nephrotoxicity (dose- and type-dependent)
Coagulopathy (reduced clotting factor activity)
Increased mortality in critically ill/septic patients (per recent meta-analyses)

Gelatins:

Mild allergic reactions
Less volume effect compared to other colloids

7. Contraindications

Severe congestive heart failure (risk of fluid overload)
Renal failure (particularly with HES and dextrans)
Active bleeding with coagulopathy (risk exacerbated by HES)
Known hypersensitivity to product components
Hypervolemia or pulmonary edema
Intracranial hemorrhage (risk of fluid shift and pressure elevation)

8. Precautions and Monitoring

Monitor central venous pressure (CVP) to assess volume status
Daily weight and urine output to evaluate fluid balance
Electrolytes and renal function, especially in elderly and ICU patients
Coagulation parameters with repeated dosing of HES or dextrans
Infusion rate: Must be tailored to the patient’s clinical condition and cardiovascular status

9. Drug Interactions

Anticoagulants: Enhanced bleeding risk with dextran or HES due to platelet inhibition
Blood products: Dextrans may interfere with cross-matching; notify the blood bank
Diuretics: Increased risk of volume shift and renal stress
Calcium-containing solutions: Avoid mixing albumin with calcium-containing IV fluids (risk of precipitation)

10. Clinical Considerations

Crystalloids (e.g., saline, lactated Ringer's) are often first-line for volume replacement due to cost, safety, and availability
Use of colloids is controversial, especially HES, which is restricted or banned in several countries due to renal and coagulopathy risks
Albumin is beneficial in:
- Large-volume paracentesis in cirrhosis
- Hepatorenal syndrome (with vasoconstrictors)
- Burn patients (after 24 hours)
Dextrans and gelatins are rarely used today in high-resource settings
Always weigh benefits vs. risks, especially in critically ill patients

11. Summary Table

Agent	Type	Key Uses	Risks
Albumin	Natural colloid	Hypovolemia, burns, cirrhosis	Fluid overload, allergy
HES	Synthetic colloid	Trauma, surgery (limited use)	Renal injury, bleeding
Dextran	Synthetic colloid	Volume expansion, microcirculation	Anaphylaxis, coagulopathy
Gelatin	Synthetic colloid	Short-term volume expansion	Allergy, weaker effect

Saidala 24

الصفحات

Monday, August 4, 2025

Plasma expanders