So take a look at this, look at
this graphic that is pretty cool.
You see the urea travels from your liver
to your kidneys through the bloodstream
Then our kidneys will filter that, send
it out of the body through your urine.
So let's do a quick review.
First we've got ammonia.
Now remember, where does ammonia come from?
Right! from the breakdown of protein.
Now here's what I want you to add to
your notes so make sure you've got that.
Protein can come from dietary or GI bleeding.
Remember, red blood cells are a source
of protein because of all the hemoglobin,
so if someone has GI bleeding they've got a
high source of protein because of that hemoglobin.
Next, urea cycle.
That the liver transforms the ammonia into
urea which travels through the bloodstream
down to the kidneys to be excreted because
the kidneys will excrete the urea in the urine, why?
because it's water-soluble
Cool, you did a great job tracking with me.
So here are the normal values
again, you got that 7-20 (mg/dL)
use lots of repetition help
yourself memorize those lab values
but now take a look at the BUN greater than 20
(mg/dL), this should start making more sense to you.
Liver or renal dysfunction, ask yourself why
would this tell me about liver or renal dysfunction?
Well because I need the liver to break apart
the protein, I need the kidneys to excrete it.
Why would upper GI bleeding cause an elevated BUN?
because blood has hemoglobin and hemoglobin is
protein, and excess protein could lead to excess ammonia.
Cool, what about high protein intake?
Same thing like upper GI bleeding that's
extra protein that my body has to process
And last, significant dehydration is the third
major category of causing an elevated BUN.
Alright now let's have some fun, I know
it's kind of nerd fun but it really is fun.
Let's think about the impact of liver failure if you're
taking care of a patient whose liver was not doing well,
what change would you expect in their BUN level?
So pause the video, think through what
you know and what changes would you expect
in a patient's BUN level who's liver failure.
Alright welcome back, hopefully you're taking
a chance to study along with us and pausing
and seeing if you can come
up with that answer yourself.
We'll always come back and give you the
right answer but it'll stick with you a lot more
if you try and do that struggle
of understanding as we go.
So the patient is in liver failure,
think about what the liver does.
It breaks down that protein, right and helps
convert ammonia into something called urea.
Right, that's all familiar to you.
So if a patient has liver failure,
their BUN is going to be decreased.
They'll have elevated ammonia and decreased BUN.
So I want to take just a minute here because
we're talking about how all your hard work and studying
pays off in actually becoming an excellent nurse.
I want to hit that ammonia level again remember it's
neurotoxic, it'll go after your central nervous system.
So anyone who has an impaired liver can
end up with elevated ammonia levels or NH3.
So you want to keep an eye on your patients
whose liver is struggling, watch that ammonia level
and it also explains why we sometimes limit dietary
intake of protein in patients whose livers are struggling.
Alright, you wrapped up your
liver, let's take a look at the kidneys.
So what change in the BUN
would you expect with renal failure?
Go ahead, try it by yourself first.
Okay cool, welcome back.
With renal failure, you're going
to see an increased the BUN.
Okay, so think that through, why do I have
elevated BUN if the kidneys aren't functioning?
Well the liver's doing it's job - it's breaking down
protein, it ends up with ammonia, it turns it into urea.
But if the kidneys can't filter appropriately,
that's just gonna to build up in the body
instead of being excreted if the
kidneys were able to handle that
Okay, so liver functioning - breaking down
ammonia, I end up with urea, everything should be fine
but once it makes it way down to the
kidneys, if the kidneys are struggling,
they can't get that out of the body into your urine.
That's why you'll see the BUN level
rise when the kidneys are struggling.