00:01
So let's start with our patient
who has hypovolemic
hypotonic hyponatremia.
00:06
That means that patient either has
true volume depletion,
because they have a low
extracellular fluid volume,
and that could be loss
of fluid volume,
or sodium from the
ECF volume
due to a variety
of different regions.
00:20
When that happens,
ADH is stimulated from a
nonosmotic mechanism.
00:24
Remember, if we lose about 10% of
our body volume,
ADH will be stimulated
in order to conserve
our vascular volume.
00:31
In so doing,
it's going to retain free water
in efforts to restore
that ECF
back to the
appropriate volume.
00:39
Physical exam will be very important
in this population
because we should see signs of
volume depletion.
00:45
The patient may be
hypotensive,
tachycardic,
they'll have flat neck veins,
or they might be orthostatic.
00:54
When we think about some
of the causes that cause
true hypotonic hypovolemic
hyponatremia,
these are things like
GI losses,
gastro neuritis that causes
stool losses or gastric losses.
01:06
Again, with those losses
you lose a lot of sodium
and patient becomes
hypovolemic.
01:12
Blood losses,
increase insensible losses,
that means excessive
sweating and burns.
01:19
And all of these situations our
urine sodium is going to be low
less than 20 mEq/L,
because we will have maximal
reabsorption of sodium
in that proximal and distal tubule.
01:30
Why? Because RAAS is activated
in these low volume states.
01:36
We can also see this
in renal sodium losses.
01:39
So in patients who, for example,
around diuretics,
who become volume depleted.
01:43
Adrenal insufficiency,
where they have difficulty
with sodium reabsorption
at that principal cell
or salt-wasting nephropathies,
things like
Bartter's and Gitelman's.
01:52
In this situation,
our patient will have
a higher in sodium.
01:56
But again,
the ADH is activated
because of their
volume depletion.