okay so welcome to another MedCram lecture this is part three of acute
renal failure we talked about b1 and creatinine and how to use it I think
that's a good background for what we're going to get into next and what we're
going to get into next is the different types of renal failure I'm going to kind
of divide the screen into thirds okay because there are three basic major
types of acute renal failure and they're aptly named one is called pre renal
failure one is just called renal failure and the other one is post renal failure
and we're going to get into what these things mean okay so you've got the
kidneys you've got blood coming to the kidneys and then the kidneys make urine
and the urine goes out through the ureter down to the bladder through the
bladder and then out through the urethra and then outside so if there's any
obstruction okay any obstruction from the ureter in the bladder and the
urethra that's going to be a post renal failure type of situation if there's any
problem with the kidney itself and I'm talking about the tubular cells I'm
talking about the glomerulus the tubular cells the collecting tubule and about
stuff then it's renal if there's a problem with the blood getting to the
kidney so if you're talking about congestive heart failure renal artery
stenosis hypovolemia hypotension any of that kind of stuff you're going to get a
pre renal sot mia kind of situation so what are some things here that could
cause pre we know let's talk about pre renal first so any kind of if there's
decreased cardiac output hypovolemia okay how about renal artery stenosis
will just abbreviate Ras so anything that prevents blood from getting to the
kidneys is going to cause that well what about renal what causes renal problems
well about medications there's tons of medications that will cause renal
failure let's name a few what about aminoglycosides so those are antibiotics
what about NSAIDs okay how about ACE inhibitors ace ace ii
ii i these are antique these are hypertensive medications so there's a
whole host of things what about just necrosis acute tubular necrosis what's
acute tubular necrosis well if there's not enough blood reaching the kidney at
first is you're gonna have a pre renal situation but if that lasts for a long
period of time long enough like i mean by hours or day you can actually get
something called acute tubular necrosis where there's just not enough blood that
rit reached the kidney there was no oxygen and the cells died and usually
this is a reversible situation but you can certainly see a TN and so a lot of
times what you're going to be doing is trying to determine is this renal renal
failure in other words is it so bad that in other words was the hypotension so
bad for so long that we have renal renal failure or is it just temporary enough
that we're dealing with pre renal failure we'll talk about how you can
figure out the difference between the two post renal failure is pretty easy
the most common cause is just prostate okay so specifically in men the
prostate is so large it's choking off the urethra and the bladder can empty
and this backs up into the ureter and it causes what we call hydronephrosis so
this is water in the kidney but there's other things that can do this cervical
cancer okay cervical cancer can spread out to the ureter and cause and
obstruction tumors any kind of tumors out there or just anything that's going
to block the the body's ability to get rid of your own kidney stones can do it
and so there's several different ways that you can go into acute renal failure
so you have to figure that out okay so let's concentrate for the moment
on these two here pre pre renal and
renal those are the two I want to concentrate on so imagine you are kidney
and if you were in a situation like this okay
imagine your situation your kidney and not enough flow is coming down the pike
not enough blood is coming down to your to your gal Mary Alice basically you
understand that as simply meaning that there's not enough volume in the body
and so what are you going to do in this situation you're going to want to hold
on to as much salt and sodium as possible and the reason is because
volume in the body is determined by the kidneys ability to reabsorb salt and so
if you've got your glomerulus so I'm going to draw a little tiny nephron here
okay and you've seen this before no doubt okay so you've got that you've got
your a for an arterial coming in and going out you are going to make sure
that every single tube you'll that you have at your disposal is reabsorbing
sodium okay so that's going to be very important and so that the urine that's
coming out is it going to be high in sodium or is it going to be low in
sodium well if you're trying to take all the sodium out of that urine as as much
as possible and getting it back into the blood so your body can get more volume
you can bet that the urinary concentration of sodium is going to be
low okay but as the sodium goes so does the water go with it so sodium gets
reabsorbed water gets reabsorbed with it what's the concentration of your urine
going to be so what's the urine osmolarity OS m it's going to be high
does that make sense so again let's review that if you've got a nephron
which is not getting a lot of flow it's going to anticipate that you're going to
need more volume and so it's going to reabsorb sodium which is the key for
getting volume sodium gets reabsorbed water follows it and so what you have is
a low urine sodium because that's what's left and what's left is going to be very
concentrated because all the sodium and the water is going to be taken out and
so you could be left with all of the other things like their urea for
instance and all the other things that the body gets rid of in the
urine so the concentration is going to be quite high now this is in Contra
distinction to what we see over here on the renal side again let's go ahead and
make our glomerulus okay here the situation is different here we've got
the flow coming down no problem but the kidneys themselves the tubules cells are
not working so if these tubules are not working tell me are they reabsorbing
sodium and water the answer is no so they're not and so what are you going to
see in the urine that passes by you're going to have urine sodium concentration
is going to be high why is that because the cells are not doing their job
they're not reabsorbing sodium like they should and as a result of that water is
not being reabsorbed and so the urine osmolarity is going to be low and
specifically it's going to be around that of the of the of the serum and it's
going to be one point zero one zero otherwise known as 10/10 ok so high
urine sodium high urine osmolarity and what we usually see is that early on it
appears as though it looks like pre renal okay whereas later on when the
kidney actually starts to fail it looks actually more like renal okay so let's
go over a couple of things that will show you how to determine how to figure
out what's going on with patients who come in with acute renal failure okay so
so so for post renal failure it's pretty easy to figure that when a patient comes
in so for post renal what you do is you put a urinary catheter in so if you
catheterize the patient put a catheter in otherwise known as a Foley catheter
and a whole bunch of urine comes out and the patient's relieved then the renal
resolves that it was probably post renal so these are pretty easy to figure out
you can get an ultrasound of the of the of the kidney you could put a Foley and
there's several ways of figuring out where the problem is so if you remember
the anatomy you've got the kidneys okay and you've
got the ureters coming down okay and they go into a bladder and then the
bladder empties out into urethra so there's several different places where
you can have an obstruction you can have an obstruction here in the ureter or you
can have an obstruction here in the urethra if you place a Foley catheter
which goes up the urethra and into the bladder and there's a lot of residual
there's a lot of fluid in there and all of it comes out well then you've got
your answer if you do an ultrasound okay and you see that these kidneys are large
because there's an obstruction here or down here then you can also make that
determination as well so ultrasound Foley catheter you can make the
diagnosis of post renal pretty well also if this patient has a history of
prostate problems and it's difficult to pass the Foley all of these are signals
that what you're dealing with here is a post renal renal failure so I don't want
to focus too much on that because what you're going to find most of your time
trying to figure out is the difference between renal and pre renal so let's
talk about that okay so let's talk about pre renal
versus renal so we're going to split the board here in two and we're going to
look at those so let's put pre renal up here pre renal again is where the heart
is not pumping enough blood or there isn't enough blood or there's a stenosis
to the artery that's going to the kidney basically there's a problem before the
kidney or pre renal okay then let's talk about renal over here okay so let's look
at different categories what about the urine osmolarity so what we say here the
urine osmolarity in pre renal is usual going to be greater than 500 whereas in
renal it's going to be less than 350 why is that again because in pre renal
you're trying to hold on to sodium in water as much as possible you're trying
to take every drop of sodium chloride and water out of that filtrate and what
you're left with is a very concentrated urine with renal on the other hand your
tubules are not working and so as a result of that you're letting stuff pass
right through and so the osmolality or the osmolarity
is very similar to that of blood and it's recall blood as molality is around
295 so it's going to be very similar to what you're getting out of the kidney
another way of saying this is this is the specific gravity specific gravity
you'll see in pre Randall is usually greater than one point zero one zero the
specific gravity and renal failure is about one point zero one zero we call it
1010 this could get up as high over here by the way as one point zero three zero
that's pretty concentrated urine there all right so the other thing we can look
at is we can actually measure the urinary sodium concentration so the
urinary sodium concentration what do you think it's going to be in pre renal it's
going to be low that's right so it's going to be less than about twenty where
is in renal you're going to see usually greater than forty you could actually
order that as a lab and see what about sediment okay what's happening with
sediment means sediment is simply dead cells from the kidney sloughing off and
finding their way ending up in the urine would you expect to see sediment in a
pre renal situation answer is no you wouldn't remember here what's the
problem the problem is there's not enough blood and fluid getting to the
kidneys and as a result of that those cells those very cells that we're
talking about there are working overtime to try to get sodium chloride up now if
there if this goes on for long enough and is severe enough the cells could die
then you switch over and you become renal because when they die
the cells are not working anymore and so they slough off and you do get positive
sediment and that's more of a renal phenomenon finally we get to the the
crux here and that's the bu n to creatinine ratio so what do we see with
a bu incretin ratio remember in pre renal bu n gets increased because it's
not being filtered as much but it also goes up for another reason because it's
being reabsorbed to the proximal convoluted tubule so typically our bu
endocrine ratios are greater than 20 whereas over here on the renal side they
are usually less than or equal to 15 now there's one other thing that I would
like to bring up and that's something that you might see called the FINA okay
FINA what's a FINA well let me let me clear the screen and show you the FINA
is actually stands for the fractional excretion of sodium of the kidney and
the equation goes something like this it is the concentration of sodium in the
urine over the concentration of sodium in the plasma all over the concentration
of creatinine in the urine over the concentration of creatinine in the
plasma complicated yes but here's the key thing I want you to zoom in on and
that is this factor right here we've already said and you know this just
algebraically that if this number is high that this number is going to be
high just algebraically and so what kind of a type of renal failure causes you to
have a high urine sodium concentration is it pre renal or is it renal
it's real because the cells are dead so what you will see if we go back and
split our screen here we got pre renal and we got renal that if you've got a
situation with a FINA okay your pre renal is usually good to be less than
one point zero if you calculate this whole thing okay
whereas with renal it's usually going to be greater than two percent
okay these are both percents it's going to be lower in the pre renal because
your urine sodium is going to be low in the pre renal and why is that because
the kidney is trying to reabsorb as much salt and water as possible okay so this
concludes acute renal failure and how to interpret creatinine B when those sorts
of things I thank you for joining