What is a Colloid Solution?
A colloid solution is a high molecular weight intravenous fluid that contains large molecules (such as albumin, hydroxyethyl starches, gelatins, or dextrans) that predominantly remain in the intravascular compartment and generate oncotic pressure, theoretically providing more sustained volume expansion than crystalloid solutions. 1, 2
Basic Composition and Mechanism
Colloids contain macromolecules that are too large to easily cross intact capillary membranes, creating an osmotic gradient that helps retain fluid within blood vessels 2
The volume expansion ratio of colloids to crystalloids is approximately 1:1, meaning colloids do not provide the dramatic volume-sparing effect once theorized 3
Intravascular persistence is greater than crystalloids, though this advantage is significantly diminished in states of capillary leak or endothelial injury 4
Types of Colloid Solutions
Natural Colloids
- Albumin: The predominant plasma protein, pooled from human donors, remains the standard against which other colloids are compared but is expensive and in limited supply 4
Synthetic Colloids
Hydroxyethyl starches (HES): Available in various molecular weights and substitution ratios; third-generation tetrastarches (HES 130/0.4) have improved safety profiles compared to older formulations 2, 5
Gelatins: Derived from bovine collagen with moderate effects on hemostasis 6
Dextrans: Polysaccharides with significant effects on coagulation and platelet function; high molecular weight dextrans have the most pronounced hemostatic effects 6, 4
Clinical Considerations and Limitations
Theoretical vs. Actual Benefits
Despite theoretical advantages, colloids have not been shown to decrease acute lung injury risk or improve survival compared to crystalloids in most clinical scenarios 4
In critically ill patients, the CRISTAL trial subgroup analysis of 741 surgical patients found no mortality difference between colloids and crystalloids 3
Adverse Effects Profile
All colloids share common risks including intravascular volume overload, dilutional coagulopathy, extravascular extravasation across leaky capillaries, and anaphylactoid reactions 7
Specific adverse effects by type:
- HES: Associated with renal dysfunction, coagulopathy (prolonged aPTT and PT), and increased transfusion requirements in ICU settings 1, 6
- Dextrans: Renal dysfunction and the most significant hemostatic interference 7
- Albumin: Myocardial depression 7
- Gelatins: Moderate coagulation effects, comparable to medium molecular weight HES 6
Hemostatic Effects
All colloids interfere with hemostasis through hemodilution and specific effects on platelet function, coagulation proteins, and fibrinolysis 6
Albumin has the least effect, while high molecular weight dextrans and HES have the most significant effects on coagulation 6
Clinical bleeding risk is primarily associated with dextrans and high molecular weight HES when safety considerations (maximum dosage, duration, patient hemostatic status) are not observed 6
Current Clinical Recommendations
The 2022 French guidelines strongly recommend against colloids in both septic shock (GRADE 1-) and hemorrhagic shock (GRADE 2-) compared to non-hypertonic crystalloids for reducing mortality and renal replacement therapy requirements 1
The 2024 Perioperative Quality Initiative strongly recommends against routine use of albumin or synthetic colloids for intraoperative fluid administration 3
Critical Pitfall
In pathological states with endothelial injury and capillary leak (precisely when colloids are commonly given), colloid molecules may leak into the interstitium and remain there, exerting an osmotic gradient that pulls additional water into the interstitium, worsening tissue edema 4