Let’s talk further about SIADH.
History and physical for sure; findings, here
Euvolemic patient, what does that mean?
What’s eu- mean, the prefix?
It means normal.
You’ve heard of euthyroid, here we have
euvolemia, what does that mean?
Even though you know for a fact your patient
has, for whatever reason, increased ADH functioning,
you’re going to reabsorb more water from
the collecting duct and one would think that
your patient, for sure, has pitting edema.
Nope, because how much sodium would you have
in your interstitium compared to a patient
who has right-sided heart failure and strictly
Decreased sodium and SIADH.
Your patient is not going to present with
pitting edema or significant pitting edema.
Serum sodium levels and plasma osmolarity,
What about urine osmolarity?
Low BUN, serum uric acid, everything is being
diluted, diluted, diluted.
Now, at the very bottom of this, it’s important,
SIADH cannot be diagnosed without excluding
hypothyroidism and adrenal insufficiency.
Once again, keep in mind that whenever you
are dealing with ADH, other endocrine dysfunctions,
especially thyroid and the adrenals, are important
for you to make sure that you rule out.
What do you want to do?
Always come to the underlying cause.
If your issue was a lung cancer, completely
different steps of management.
If your patient was on drugs, which is carbamezapine,
obviously remove the offending agent.
Whatever it may be, you want to keep things
in mind, pulmonary disease and treatment,
cessation of drugs, hormonal replacement and
adrenal insufficiency or even perhaps hypothyroidism.
These are things that you are paying attention
to when dealing with SIADH.
Restrict free water intake.
Here, once again, caution must be exercised
with patients with SIADH secondary to subarachnoid
haemorrhage due to exacerbation of the vasospasms
and infarction from the drop in blood pressure.
Keep that in mind.
So, if your patient, extremely important clinical
point, is the fact that if there is going
to be head trauma and it’s due to subarachnoid
haemorrhage, be very, very careful because
if there is going to be ADH and vasospasm,
it only makes matters worst up in the brain.
That’s a huge clinical point that you can
use for every single board that is ever presented
Restrict your free water intake please with
SIADH, your patient is already extremely hypervolemic.
Let’s talk about the use of IV saline and
The first thing you’re thinking to yourself,
“Dr. Raj, you just said your patient is
hypervolemic, you said-you said restrict free
That is correct.
Free water is not sodium, is it?
No, it’s free water.
If your patient’s hypervolemic and already
is reabsorbing too much water, why would you
want to give more free water?
So, that does not help you with management.
Now, that free water that you are reabsorbing
from the collecting duct, does what to sodium?
You want to make sure that you replenish the
What’s IV saline?
Oh, Na, here you go… sea of-sea of IV saline.
Now, if you want to... objective is to increase
the sodium concentration, what you want to
keep in mind for your board exam is the following
that electrolyte concentration of fluid given
must exceed the electrolyte concentration
of the urine and not simply the plasma because
here the plasma is not going to be a proper
indicator as to how much sodium is actually
in your patient, but if you’re able to measure
your sodium urine or urine sodium then that
is what is going to be your actual control
or your measurement.
IV saline, why?
Because your patient is hyponatremic.
However, the only thing that you want to worry
is the fact with any time you’re giving
IV saline, whatever the indication may be,
dehydration, maybe SIADH, so and so forth,
is that you never give it rapidly because
if doing so then you’re always worried about
an interesting side effect, but nonetheless,
incredibly significant called central pontine
SIADH pharmacologically… high salt in conjunction
with loop diuretic.
Remember, you are trying to get rid of this.
Now, is all the loop diuretic going to be
Well, it all depends, but sodium is going
to be incredibly important.
Vasopressin receptor antagonists is what you’re
thinking about here.
Because there’s too much SIADH, we’ll
talk about these in a second, and you have
a particular V2 receptor blocker known as
conivaptan and this is then given as IV only,
V2 receptor blocker.
Pharmacologically speaking, with vaptan as
being a V2 receptor blocker, we have an oral
analog known as tolvaptan and interesting
enough, you have demeclocycline and lithium.
Stop here for one second.
The boards will ask you the following.
Here’s a-Here’s a patient that requires
demeclocycline, here is a patient that is
bipolar taking lithium.
This, ladies and gentlemen, will bring about
nephrogenic diabetes insipidus that we do
Now, your patient has SIADH and the patient
with SIADH where there’s too much V2 receptor
activity, wouldn’t you want to then induce
nephrogenic diabetes insipidus?
And that’s the thinking that you must have
here when dealing with demeclocycline and
Antagonize ADH in action and can be used in
a rare patient who cannot be treated with
vaptan the drugs mentioned above.
Steps of management… restrict free water
IV saline is important so that you...
Get rid of that fluid if you’re thinking
about loop diuretic, but once again keep in
mind of the sodium levels.
V2 receptor blockers and these are your vaptan
drugs: conivaptan, IV, tolvaptan, your PO
If these are refractory, then you start thinking
about drugs such as demeclocycline and lithium.