By Adem Lewis / in , , , , , , , , , , , , , , , , , , , , , , /


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


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