Saline is where we are and going to little
bit technicality, but I am just going to give you
a brief little overview of saline without
going to enough detail where number 1 is irrelevant.
Anything is irrelevant at this point. It is
not even included in any of my lecture series.
You understand that. Everything that I have
been giving you is high yield. So, therefore,
you don't hear me say high yield
because there would be a waste
of your time. Everything is high yield. Everything
that I am giving you is a story about something
significant in some way, shape or form. It is
going to be asked. I can guarantee you that.
Okay. So come with the saline. It is NaCl
that much we do know. Next, it is isotonic.
Now, what is interesting about isotonic is
that you look at this and you see 154 and
right off the bat, you will know that does
not mean isotonic. Isotonic means approximately
how much? Approximately 300. So what does
this 154 then refer to? Each electrolyte, Na
cation, chloride, anion, each electrolyte
has a mmol/L unit of 154.
But Dr. Raj, if there is two of them and each one is 154,
don't you get 308?
That is correct. So technically speaking you are
telling me Dr. Raj that therefore saline
NaCl at 308 is slightly hypertonic. Yes, that
is exactly what I am saying. Nothing is ever
perfect, but this is as close to isotonic
saline as you can get. We have therefore
0.9 percent. So it is not 100 percent that you
would be using for being isotonic for obvious
reasons. It really is a little bit more hypertonic.
A 0.9 percent that is the calculation that
you would use or shall I say 0.9 percent is
the value that you want to know as it being
isotonic. Let me give you another example.
We have talked about the following. You have
injected your patient with isotonic saline
slowly over a course of 24 hour period right?
Why slowly? Because if you gave isotonic saline
too quickly, what is the diagnosis that you
or what is the disease or dysfunction that
you are then going to manifest in the patient?
It is called central pontine myelinolysis.
We have discussed that earlier. So slowly.
But if you by chance give too much NaCl, then
you are filling up the entire ECF, you might
then be in a state of hypervolemia. What happens
to ECF volume? It increases. Is there any
other change, yes or no in any of the total
body water compartments? No. The only change
was what? ECF volume. No change in osmolarity
either in the ECF or ICF. That we have discussed.
If you want a little bit more detail in terms
of the litres and the units and such, there
it is at this point you are good with knowing
0.9 percent. Okay now, this discussion is
important. I need you to understand the terminology
of half normal saline. So if one half is normal
saline, what is saline? NaCl okay. Saline
is NaCl. So if half of your solution is NaCl,
saline, what is the other half? Water. What
is the difference in terms of distribution?
Before we move on, let us now predict what
you can expect on predict as far as distribution
of the fluids. If it is going to be half normal
saline, tell me about that saline. That saline
will only be distributed in which compartment?
I am sorry, what did you say? Only in the
ECF, good. So the saline component of this
is only going to be distributed in the ECF.
Tell me what are the fractions that you want
to know. 3/4, 1/4.
3/4 interstitium, 1/4 plasma.
Stop there. What about the other half?
The other half was pure water. Okay. That
pure water, tell me about its distribution
throughout the total body water. Throughout,
what does that mean? That means 1/3
of water will go into where? Good. It will
go into ECF. 2/3 of it will go into
the ICF and then from there, that 1/3
you will divide it into 3/4 and 1/4.
Is this too much detail? No. This is expected
of you as being a fresher medical school student
or a resident. Ya. Ultimately how often would
you use IV fluids? All the time. So it is
imperative that you at least know a few differences
here and what it truly means to be normal saline
versus half-normal saline. And if it is half
normal, what is half of nine? There you go.
Take a look. 0.45. Why I say 9? Because normal
is what? 0.9. Our thing is coming together.
Before we move on, one last thing. If each
electrolyte had a millimole of 154 and you
taken half of it, then this thing brings
us to 77. Seventy-seven is designated for
each electrolyte. Thus when you add them both,
how much do you get? 154. Is 154 normal plasma
osmolarity? Yes or no? Not at all. What is
normal plasma osmolarity? Approximately 300.
So what kind of solution is half-normal saline?
It is hypotonic fluid. Is it not, conceptually?
So things that you want to keep in mind. That
was a little bit of math, a little bit of
calculation, let's put things together and as
we do so, I am going to walk you through the
concepts. That is the most important thing.
You as a clinician, you as a doctor are always
thriving for concepts. Once you get the concepts
down, then you can put in the math as you
wish. But conceptually, one can think of the
following, we have examples here. Let's do
half normal saline. What does that mean to
you? Half water, half saline. The half of
the water, which is our first component here,
what does it do? Look. Equally distributed
through TBW. What is highlighted here in red?
The total body water includes 2/3 of
ICF, 1/3 of your ECF. What about the other
half? The other half is saline. Where are
you only going to distribute? Can you predict
this? Good. There you have it, ECF. 3/4
interstitium, 1/4 plasma. Did you ever
think that something that you learned way
back in physio in terms of basic concepts
of total body water, will become so incredibly
crucial for you to understand the pathology?
We have spent quite a bit of time with total
body water compartments with all kinds of
diseases and now we are finishing it up. We are
adding the icing with IV fluids. Now, what
is going to happen to the first quarter? What
does that mean? The quarter is referring to
the quarter saline. That would mean only 1/4
of this is saline and what about that 1/4?
Now we can do a little bit math here, can't
we? A litre of quarter normal saline. What
is a litre? 1,000 mL. Clear.
Of the 1,000 mL, and I am then
giving your patient quarter normal saline,
how can you think of this? We will divide
this into of the saline, you then take your
free water, which is going to be 750. Because
only a quarter of this is saline. 750 is what?
You tell me about that water and distribution.
You got this down? What about that water? Throughout
total body water. ECF, ICF, all throughout
it and what does that quarter mean? 250 would
be your saline and tell me about that 250.
Good. It will be distributed between your
ECF only. This is what kind of fluid? Once
again hypertonic. So now we have normal saline,
half-normal saline, quarter normal saline.
This differs down we have added a little bit of math
with one litre of quarter normal. Let us continue.