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

welcome to another MedCram lecture
we’re going to talk about hypernatremia not hyponatremia but hypernatremia and
this is defined as any sodium concentration that is greater than 145
now just as a reminder anything that ends in letters amia refers to something
that is in the blood so we’re talking about an elevated sodium concentration
that is in the blood now if you want to know about hyponatremia please refer to
our hyponatremia lectures now if you may recall when someone has hyponatremia the
first thing that you need to do is you need to figure out whether it is
hypertonic isotonic or hypotonic and then you need to figure out if it’s
hypovolemic hypervolemic or iso bulimic with hypernatremia however almost all of
these issues with hypernatremia are also hypertonic which means that the tonicity
of the serum is high so the next thing you need to figure out when you have
someone that has a high sodium concentration on their blood test is to
figure out what it’s due to is you’ve just got to figure out what the volume
is of the patient what is the volume and that simply is is the volume too high or
hyper valley m’q is it too low from hypovolemia or is it the same what we
call ice oval emia the first thing we’ll talk about is actually gonna be hypo
bulimic hyponatremia then we’ll talk about hyper voll emic hyponatremia and
then we’ll talk about ISO vole emic hyper natrium iya so I’m gonna divide
the screen into three areas the first one is gonna be hypovolemic hyponatremia
the next one we’ll talk about after that is hyper bulimic hyper nutri Mia and
let’s pick a nice blue color here then we’ll talk about ISO the lemic hyper
tree mia so basically we’ve got peep
who have high sodium’s who look like they don’t have a lot of fluid we have
people with high sodium’s that look like they have a lot of fluid and we have
people with high sodium’s that look like their volume status is about the same by
far the most common is the hypovolemic hyponatremia these by definition are
people who have lost salt and water but they’ve actually lost more water than
they have salt and as a result of that their sodium concentration in their body
goes up so the key here is they’ve lost lots of water and sodium but they’ve
lost more water than sodium and the way I want to show that is through a graph
now this is a similar graph that we used in our hyponatremia talk now this is a
graph here which graphs sodium concentration on the y-axis and volume
on the x axis this area is the intra cellular fluid and this is the extra
cellular fluid so what first happens here is that the patient is losing water
and sodium both and as a result of that when they’re losing water and salt both
all you’re going to have is a reduction in volume but because the patient is
losing more water than salt their sodium concentration is going to go up now when
the sodium concentration goes up on the extracellular side what’s going to
happen is water is going to go from the intracellular side to the extracellular
side to offset that high sodium concentration and as a result the sodium
concentration in the intracellular fluid will also go up and it will lose some of
its volume and so this is what you will have yellow meaning the pathological
process white being the normal ok so again you lose volume and water and as a
result of that sodium nutrition goes up and of course the
sodium concentration in the intracellular side and the extracellular
side should always be the same because water can freely go through that
permeable membrane and as a result you lose intra cellular volume as well now
there’s two reasons why this could happen there is the non renal reason and
of course there is the renal now what would be the non renal reason why
someone would lose this well if they were having sweating or diarrhea or
probably the most common reason that I see is they’re elderly they’re in a
nursing home and they have these insensible losses but they can’t get up
to get a drink of water and so I see these patients coming in from the
nursing home with high sodium’s and they look very dry and they fit into this
category and the most likely reason is this because they’re just becoming
dehydrated so how do I know what’s the hallmark of that well you know that if
the kidney is not getting enough blood flow it’s gonna want to hold on to as
much sodium as possible and so therefore the telltale sign that this is a non
renal hypovolemic hyponatremia is that the sodium concentration is going to be
less than 10 in the urine okay now what about renal what are some renal causes
for a hypovolemic hyper maitreya well you could have an osmotic diuresis
and what would be the reason for that well if you have a bleed in the brain
patient and they’re on mannitol okay so we give a man at all that’s gonna cause
a diaeresis getting rid of free water through this osmotic diuresis through
the kidney and that’s gonna cause the sodium concentration to go up
what’s the telltale sign well obviously if you know the patients on mannitol
that’ll explain it but here the urine concentration of sodium is going to be
greater than 20 so what’s the treatment for this the treatment for a hypovolemic
hyponatremia is what do you think if you’re losing salt and water the
treatment is going to be normal saline so we have these patients coming in from
the nursing home that are dehydrated and their sodium is high we don’t want to
just give them water we want to give them salt and water and this is kind of
paradoxical because you’re saying to yourself well this patient’s sodium is
elevated well that’s true their sodium is
elevated but they’re also volume deficient and so in these cases even
though they’re sodium’s maybe in the 150s
I give normal saline because I know that they are behind in volume and it’s only
once you correct that volume if their sodium is still high then I will go
ahead and give them free water but I will never give them free water first
because what happens when I give free water free water will only correct the
concentration of sodium that’s elevated it will not correct this volume because
remember free water gets distributed throughout the entire system and this is
what I want to correct first is the volume deficit and that’s why I give
normal saline okay let’s talk about hypervolemic hyponatremia it’s kind of
rare don’t see it much wouldn’t jump to the conclusion that that’s what it is
when I see it in a patient but what’s going on here is you’re getting lots of
sodium retention in fact you’re retaining salt plus water but guess what
you’re retaining more of you’re retaining more sodium than you are
water and what are some reasons why you could do this over resuscitation with IV
fluids okay so IV fluids could do it or in a
code situation if you’re giving a lot of sodium bicarbonate in a code situation
I’ve seen that before so that’s predominantly how that happens
now in terms of why this could be caused this would be what we call a non renal
reason or excess of fluids but what else could happen well before we get to that
let’s actually draw a picture and show what’s going on so let’s draw our normal
situation here’s our extra cellular fluid is our
intra cellular fluid so we’ve said here that we had retention of sodium and
water but more sodium than water so what’s the first thing that’s going to
happen the first thing that is gonna happen is we’re gonna have sodium and
water giving us a larger volume but because we’re also retaining more salt
than water our extracellular fluid compartment is
going to go up in concentration now as a result of that higher concentration
intracellular fluid is going to shift into the extracellular fluid water is
going to go through that semi permeable membrane and as a result of that water
leaving the sodium concentration is going to go up in that intracellular
fluid compartment and it will have less volume so this is the shift that we will
see now what’s another reason in addition to IV fluids and sodium
bicarbonate well there’s another thing that could cause it and that is mineral
corticoid excess we see this in things like Cushing syndrome remember in our
adrenal cortex in the zona glomerulosa there is a hormone called aldosterone
aldosterone causes sodium reabsorption and potassium excretion in the distal
convoluted tubule this excessive mineral corticoid secretion could cause elevated
sodium levels and exactly this sort of estate so what’s the treatment well if
we’re retaining too much sodium and water in this situation then diuretics
should work especially those that cause salt wasting and of course giving free
water will not hurt either okay let’s talk about ice oval emic so here we’re
not losing volume that’s the key there is ice oval emic means no loss in volume
but what we are seeing here is loss of free water just simple free water is
being lost so what would be the non renal reasons
this would be well if we’re losing free water it could be simply that we’re no
longer retaining that free water the other possibility is is that if we’re
losing that free water it’s because we no longer have the antidiuretic hormone
which as you recall works on the collecting tube you’ll to reabsorb free
water from the collecting tube you’ll remember the nephron looks like this
loop of Henle and then you have the collecting tube you’ll remember that the
ADH works here to reabsorb free water if for some reason the brain is not
secreting ADH this would be the opposite of the syndrome of inappropriate ADH
this would be like what we call a diabetes insipidus the other
possibilities you could get nephrogenic diabetes insipidus nephrogenic diabetes
insipidus is where the kidney is not responding to the antidiuretic hormone
okay so there’s a number of reasons why either you’re not secreting enough
antidiuretic hormone from the posterior pituitary or not making it in the
hypothalamus or the collecting tubules is simply not responding to it and you
get a nephrogenic diabetes insipidus the treatment in all of these situations is
simply free water replacement just free water so how is that going to look in
terms of our diagram again here’s our extracellular fluid compartment
extracellular fluid and then intracellular fluid so again here we are
simply losing free water and so what is that going to look like well we’re not
actually changing volume here the volume is the same so all we see is since free
water is being lost the concentration of the extracellular fluid is going to go
up now as a result of the extracellular fluid going up what’s going to happen water is going to go from the
intracellular fluid over to the extracellular fluid and as a result of
that you’re going to lose intracellular fluid compartment space and in a lot of
cases here this volume line doesn’t they move much from where it started you
notice how it doesn’t move much it might move a little bit but it’s not gonna
move very much and that is the reason why it’s called I so polemic again the
treatment is free water so I would recommend that if this doesn’t make a
lot of sense to you go ahead and review our hyponatremia lecture also review our
adrenal gland lecture and make sure that you understand what it is that’s going
on there thanks for joining us

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