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