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 that just as a reminder anything that
ends in the word or the letters emia 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 hypo 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 mech 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
going to be hypovolemic hyponatremia then we'll talk about hyper voli m'q
hyponatremia and then we'll talk about ISO vole emic hyper natrium iya so I'm
going to divide the screen into three areas the first one is going to be
hypovolemic hyper
Nate remya so we can talk about that one the next one we'll talk about after that
is hyper bulimic hyper tree Mia and let's pick a nice blue color here then
we'll talk about ISO Philemon hyper tree Mia okay so basically we've got people
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 kind of show that is through a
graph now this is kind of the graph a similar graph that we used in our
hyponatremia talk and I'm going to kind of use the similar status now this is a
graph here which graph 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 soda in 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 okay 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 concentration 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 okay there is the non renal
reason non renal and of course there is the renal now why would 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 is because they're just
becoming the hydrated 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 going to 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 hyponatremia 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 going to cause a diaeresis getting rid of free water
through this osmotic diuresis through the kidney and that's going to 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 your retaining
salt plus water but guess what you're retaining more of you're retaining more
sodium than you are water and a lot of things can happen here you could get
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 you'll I've seen that before
so that's that's predominantly how that happens now in terms of why this could
be caused this would be a what we call a non renal reason or a 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 intracellular fluid here's our extra cellular fluid is our intracellular
fluid so we 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 going to happen is we're going to 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
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 tubules this excessive mineral corticoid
secretion could cause elevated sodium levels and exactly this sort of a state
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 why 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 tubular the
Efrain 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 not
you're not secreting enough antidiuretic hormone from the posterior pituitary and
not we're not making it in the hypothalamus or the collecting tube
you'll is simply not responding to it and you get a nephrogenic diabetes
insipidus the treatments 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 is our extracellular fluid compartment extracellular fluid
and then intracellular fluid okay 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
really move much from where it started you notice how it doesn't move much it
might move a little bit but it's not going to move very much and that is the
reason why it's called ISO 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
you