In this review, we will cover colloid solutions vs. crystalloid solutions.
Both of these are solutions that are administered to the intravascular space and expand the plasma volume.
What does it mean to expand plasma volume? This means we’re adding more fluid into the blood vessels (hence plasma).
Colloid Solutions
First, let’s review colloid solutions. These solutions can include natural and synthetic types of fluids. For example, a natural type of colloid solution is known as albumin (a protein) and blood products. Whereas, synthetic types include Dextran, Hydroxyethyl starches (HES), and gelatin.
How do these fluids work? They work by pulling water into the intravascular space, but how do they do this?
Colloid solutions contain molecules that are very large molecules (proteins are very large). When these large molecules enter the intravascular space, they are unable to escape the capillary wall. Because they are unable to escape (but stay in the intravascular space longer), there are a high concentration of them in this space. This high concentration creates oncotic pressure, also known as colloidal osmotic pressure.
What does this do? This results in water being pulled from around the blood vessels (hence interstitial fluid) to the blood vessel, which is the intravascular space. This will expand the fluid volume inside this space, which is extremely helpful in conditions like:
- Hypovolemic shock
- Severe burns
- Extreme bleeding
The reason they are effective at treating these emergency situations is because they are fast at expanding this space. They have a tremendous pulling effect on the water from the surrounding tissues, which helps increase fluid volume to the depleted intravascular space. In addition, the amount of colloidal solution administered typically equals the amount of fluid depleted from the system, which is not the case with crystalloid solutions.
Downside of Colloid Solutions? Two big things are that they can cause the patient an allergic reaction and coagulation problems. Therefore, as the nurse we must monitor for these reactions (for more colloid solution nursing interventions). Furthermore, these solutions are not usually readily available and tend to cost more for the patient.
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Crystalloid Solutions
Crystalloids solutions include hypertonic hypotonic and isotonic fluids. These bags of solutions contain fluid (like water, saline etc.), but also have electrolytes (like sodium, potassium etc.) in them.
Electrolytes are small molecules that don’t hang out too long in the intravascular space like colloids. They can expand the intravascular space by shifting fluid around through osmosis. The way the fluid shifts water around depends on the tonicity of the fluid.
For example, crystalloid solutions that have a high tonicity are known as hypertonic fluids. These fluids have a higher amount of solutes (electrolytes) in them compared to the blood. This causes water to be pulled from the cell (intracellular space) to the outside of the cell (extracellular space: this includes the intravascular space). This can dehydrate or shrink the cell, which may be needed in cases of cerebral edema.
On the flip side, crystalloid solutions that have a lower tonicity are called hypotonic fluids. These fluids have a lower amount of solutes (electrolytes) in them compared to the blood. This causes water to be pulled from the outside of the cell (extracellular space: this includes the intravascular space) to the cell (intracellular space). This can lead to cell swelling. However, this may be beneficial if the cell was dehydrated.
Then, there are crystalloid solutions that have an equal tonicity called isotonic fluids. These fluids have the same amount of solutes (electrolytes) in them compared to the blood. Due to this, there isn’t a mass movement of water from the intracellular to extracellular space. These fluids are beneficial at replacing fluid to the intravascular space.
Downsides of crystalloid solutions? These fluids are not as fast at expanding the intravascular space like colloids. In addition, the patient will need a high volume of these fluids to equal the amount lost. This carries the risk of fluid volume overload.
However, there is not the risk of allergic reactions or coagulation problems, and they are easily accessible and inexpensive.
Quick Comparison Chart on Colloids vs. Crystalloids
You may be interested in Colloid Quiz or Crystalloid Quiz.
References:
Dengue Clinical Case Management E-learning. (2023). Crystalloid & Colloid IV Solutions: Intravenous Fluids. Retrieved from https://www.cdc.gov/dengue/training/cme/ccm/page70749.html.
Lewis SR, Pritchard MW, Evans DJ, Butler AR, Alderson P, Smith AF, Roberts I. Colloids versus crystalloids for fluid resuscitation in critically ill people. Cochrane Database Syst Rev. 2018 Aug 3;8(8):CD000567. doi: 10.1002/14651858.CD000567.pub7. PMID: 30073665; PMCID: PMC6513027.
III, J. L. L. (2023, April 18). Volume overload – endocrine and metabolic disorders. Merck Manuals Professional Edition. https://www.merckmanuals.com/professional/endocrine-and-metabolic-disorders/fluid-metabolism/volume-