Colloids are solutions containing larger molecules, such as proteins or starches, that remain in the intravascular space for a more extended period, providing a longer-lasting volume expansion. The main types include:
Albumin (Human Albumin Solution):
A natural colloid derived from human plasma, available in concentrations of 4-5% or 20-25%. Albumin is effective for volume expansion and can reduce edema in patients with hypoalbuminemia. It is often used in critical care settings, such as sepsis or acute respiratory distress syndrome (ARDS). However, it is more expensive and has limited availability due to being a blood product, which may pose a risk of allergic reactions or transmission of infectious agents.
Hydroxyethyl Starch (HES):
Synthetic colloids like HES (e.g., Voluven, Hespan) are commonly used for volume resuscitation. They offer effective volume expansion but have been associated with an increased risk of kidney injury, coagulopathy, and higher mortality rates in critically ill patients, particularly those with sepsis. In the United States, hydroxyethyl starch products now carry an FDA boxed warning for increased mortality, kidney injury requiring renal replacement therapy, and excess bleeding; they are reserved for situations where no adequate alternative exists.
Gelatins:
Gelatins (e.g., Gelofusine) are derived from bovine collagen and are used as volume expanders with a relatively short duration of action. They are less expensive than albumin but can cause allergic reactions, including anaphylaxis. Additionally, they may not provide as much intravascular volume expansion as other colloids.
Dextrans:
Synthetic glucose polymers like Dextran 40 and Dextran 70 offer effective volume expansion and improved microcirculatory flow. However, their use is limited due to significant side effects, including bleeding, anaphylactic reactions, and interference with blood cross-matching.
Advantages
- Provide more sustained intravascular volume expansion.
- Lower risk of tissue edema compared to crystalloids.
- Beneficial in patients with significant hypoalbuminemia or requiring rapid volume expansion.
Drawbacks
- They are more expensive and less readily available than crystalloids.
- Potential for adverse effects, such as coagulopathy, kidney injury, or allergic reactions.
- Certain colloids (e.g., HES, dextrans) are associated with specific complications and are generally contraindicated in critically ill patients.
Anesthesia providers can make more informed decisions on fluid management strategies tailored to individual patient needs and clinical contexts by understanding the various types of crystalloids and colloids.
| Feature | Crystalloids | Colloids |
|---|---|---|
| Composition | Small molecules that pass easily through semi-permeable membranes | Larger molecules — proteins or starches — that stay in the intravascular space longer |
| Volume expansion | Rapid, but less sustained | More sustained intravascular expansion |
| Edema risk | Can cause edema and tissue swelling if overused | Lower risk of tissue edema |
| Cost and availability | Cost-effective and widely available | More expensive and less readily available |
| Main drawbacks | Dilutional coagulopathy or electrolyte imbalance with excessive use | Coagulopathy, kidney injury, allergic reactions; HES and dextrans are generally contraindicated in critically ill patients |
| Where they fit | Primary choice for fluid resuscitation, with the type tailored to the scenario | Significant hypoalbuminemia or a need for rapid volume expansion |
