What is Oncotic Pressure?

Nursing Students Student Assist

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I've been stuck on this topic for almost an hour now and I think I've got it. So Oncotic pressure is the pressure generated by Albumin proteins in the Plasma that forces fluids such as water from the intercellular space to move into the RBC?

This is the answer I'm planning to give for my test coming up in a few days as my Professor asks what Oncotic Pressure is.

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Not necessarily just albumin but big proteins (or colloids) in general force fluid from tissue space back into the venule side of the capillary bed. It's the only pressure that drives fluid back into circulation!

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I do not understand what you said. Let me explain.

Albumin and other large proteins and as the user above said PULL water from the interstitial space into the intravascular space.

You have the intersticial space

Within it you have cells

(Cells) (cells)

-------------------------------------

On the other side you have the intravascular space

I want you to go back to basics...

Remember that WATER follows sodium?

This is similar ... the water on the intersticial side will go to the intravascular side .... PROVIDED there's enough albumin to drive this... if NOT as seen in cirrhosis, you'll see ascites.

Tell me what TWO conditions in which hypoalbuminemia is present?

Hint ... one is with liver and one is with kidneys

Also, while we're on the topic. Albumin is pretty important. Apart from driving oncotic pressure it also binds to drugs. Some drugs like NSAIDs and Digoxin bind to albumin. So what does this tell us about patients with LOW albumin levels? Increased risk of toxicity? ;)

Albumin also is implicated with acid/base balance because it's negatively charged ... it's an anion.

Please refer to the visual to understand oncotic pressure.

http://fce-study.netdna-ssl.com/images/upload-flashcards/883783/522194_m.jpg

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Specializes in Critical Care, ED, Cath lab, CTPAC,Trauma.
Intravascular or intracapillary oncotic pressure is determined by plasma proteins in the bloodstream. The proteins keep fluid in the blood vessel, with albumin protein molecules doing 70% of the work

These resources might help

Nursing Center - CE Article

CV Physiology: Hydrostatic and Oncotic Pressures

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It's not really a physical pressure, like, oh, the pressure it takes you to push over a pile of blocks. It's a force that results in movement of the fluid.

There's protein and (essentially) water or saline in a blood vessel. There ought to be a nice balance, where the blood isn't so thick with extra protein that it sucks water out of surrounding cells, or so thin and protein-poor that fluid leaks away because there isn't enough protein to hold it in the blood vessel.

This is why people with low serum proteins have edema -- they don't have the oncotic pressure (that isn't really pressure, remember, it's a force) to keep the fluid in the vessels.

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