What exactly is the difference between crystalloids and colloids?

In summary, colloids and crystalloids are both volume and plasma expanders, but colloids are iso-oncotic and therefore do not cause fluid shift between the interstitial and intravascular space. Crystalloids, on the other hand, are not iso-oncotic and require a larger volume to achieve the same degree of blood volume expansion, leading to more hemodilution. Hypo/hypertonic solutions can also affect the amount of water within cells, but this is a separate issue from the difference between colloids and crystalloids.
  • #1
sameeralord
662
3
Hello guys,

I'm bit confused here, hope you guys can help me out.

1. Crystalloid- Ok they contain water soluble molecules. So eg is Saline (NaCl). Now book says if I infuse crystalloids then only 1/3 of of my infusion would remain in the intravascular compartment. Now my question is why is this? If I add lot of salt to intravascular compartment eg by giving saline, shouldn't I suck more water from extracellular compartment, why am I losing 2/3 instead.

What I think: Is it because Saline contains like 0.9% Saline. So this is actually more like you are adding more water to the intravascular compartment rather than salts, so some water may leak out. Does this mean if I give 5% Saline solution more water would stay in the intravascular compartment than 0/9%.

2. Colloid- Ok why are they called plasma expanders

What I think: Ok they are big molecules, increasing colloid osmotic pressure and sucking water from extracellular environment into blood vessels. But crystalloids should also then be considered plasma expanders because add the end, they also increase the fluid even if it is not as great as colloids.

Thanks a lot in advance. :smile:
 
Biology news on Phys.org
  • #2
Normal saline contains roughly the same osmolarity of NaCl as blood. It is a crystalloid because it contains a water-soluble molecule.

If you used a saline solution with a larger concentration of salt then it would act to induce a shift in fluid from the intracellular to the extracellular space due to the osmotic gradient (hypertonic saline is therefore effective at reducing intracranial pressure as it decreases brain water).

Colloids contain larger molecules that are (for the most part) not water-soluble e.g. toothpaste (sorry for the non-medical example, I'm a chemical engineer ^_^).

They are both volume expanders and plasma expanders. More information on the respective advantages / disadvantages of each can be found here:

http://www.nursingtimes.net/nursing...colloid-and-crystalloid-fluids/204444.article

Hope this helps!
 
  • #3
Shisnu said:
If you used a saline solution with a larger concentration of salt then it would act to induce a shift in fluid from the intracellular to the extracellular space due to the osmotic gradient (hypertonic saline is therefore effective at reducing intracranial pressure as it decreases brain water).

Hey, Thanks for the reply :smile: However in this scenario if I add salt into intravascular compartment, wouldn't that make it more hypertonic, so shouldn't water from outside come in, instead. Why have you stated the opposite? Did I missunderstand something.

EDIT: Oh wait are u saying? If I add salt to blood vessels, water from red blood cells for example would come out increasing intravascular compartment, then this excess water would go out of the intravascular compartment due to increase hydrostatic pressure inside the vessels, so you lose some water from crystalloids.
 
  • #4
The following is how I understand it. If I am wrong then someone please correct me.

Colloids are iso-oncotic with blood plasma, which means that they do not affect the force causing fluid transfer from the interstitial fluid to the blood plasma. Giving someone a colloid solution will cause the plasma to expand, expanding the volume of the blood. Some hemodilution will occur and the increased hydrostatic pressure (the force causing fluid transfer from the blood plasma to the interstitial fluid) may cause some fluid to leak out into the interstitial and transcellular spaces, but for the most part with colloid solutions whatever you put in stays in the blood.

Keeping it simple, isotonic crystalloids have roughly the same osmotic pressure as the extracellular fluid in general, but are NOT iso-oncotic with blood plasma. Therefore when you give someone a crystalloid solution the hydrostatic / osmotic pressure difference between the interstitial fluid and blood plasma is changed, and the replacement fluid will distribute between the two. Therefore crystalloid solutions require a larger volume of replacement solution to achieve the same degree of blood volume expansion achievable with a colloid solution, thus also increasing the degree of hemodilution.

You can alter the amount of water within cells by using hypo/hypertonic solutions (i.e. my point about intracranial pressure). However I now realize that was a digression from your original question, so apologies if this caused any confusion. The main difference between colloids and crystalloids that I think you are concerned about is that colloids are iso-oncotic, whereas crystalloids are typically merely isotonic. For the physical differences, see my previous post.
 
  • #5


Hello there,

The main difference between crystalloids and colloids lies in their molecular size and ability to stay within the intravascular compartment. Crystalloids, such as saline, contain small molecules that can easily cross cell membranes and distribute evenly throughout the body's compartments. As a result, only 1/3 of the infused fluid remains in the intravascular compartment, while the remaining 2/3 is distributed to the extracellular and intracellular compartments.

On the other hand, colloids are larger molecules that are unable to cross cell membranes. When infused, they stay within the intravascular compartment and increase the colloid osmotic pressure, causing water to be pulled from the extracellular compartment into the blood vessels. This is why they are called plasma expanders - they expand the intravascular volume by drawing in water from the surrounding tissues.

In terms of your question about 5% saline solution, it would still behave like a crystalloid and only 1/3 of the infused fluid would remain in the intravascular compartment. The concentration of saline does not significantly affect its ability to distribute throughout the body.

I hope this helps clarify the difference between crystalloids and colloids. If you have any further questions, please don't hesitate to ask. As a scientist, it's important to fully understand the mechanisms and differences between different types of fluids used in medical treatments. Keep up the curiosity and critical thinking!
 

What is the definition of crystalloids and colloids?

Crystalloids and colloids are two types of fluids used in medical settings to treat conditions such as dehydration and shock. Crystalloids are solutions made up of small molecules that can easily pass through cell membranes, while colloids are solutions made up of larger molecules that do not easily pass through cell membranes.

What are some examples of crystalloids and colloids?

Common examples of crystalloids include normal saline, lactated Ringer's solution, and dextrose solutions. Examples of colloids include albumin, hydroxyethyl starch, and gelatin solutions.

What are the main differences between crystalloids and colloids?

The main difference between crystalloids and colloids lies in the size of their molecules. Crystalloids have smaller molecules and can easily move across cell membranes, while colloids have larger molecules and are unable to pass through cell membranes. Additionally, crystalloids are less expensive and have a shorter duration of action compared to colloids.

When should crystalloids be used over colloids?

Crystalloids are typically used in cases of mild to moderate dehydration or shock, as they are effective at restoring fluid volume and electrolyte balance. They are also preferred in cases of burns, as they can help with tissue perfusion. Colloids, on the other hand, are typically reserved for more severe cases of dehydration or shock, or for patients who are unable to tolerate large volumes of fluid.

Are there any risks or side effects associated with using crystalloids or colloids?

Both crystalloids and colloids can have potential side effects and risks, which may include allergic reactions, electrolyte imbalances, and fluid overload. It is important to carefully monitor patients and use these fluids as directed by a healthcare professional.

Similar threads

Replies
7
Views
4K
  • Chemistry
Replies
1
Views
4K
Replies
8
Views
8K
  • Materials and Chemical Engineering
Replies
11
Views
3K
Replies
9
Views
3K
Replies
1
Views
1K
  • Feedback and Announcements
Replies
16
Views
3K
Replies
2
Views
3K
Back
Top