As to 1 litre of normal saline.
Can we do this
quickly? Yes, you can. One litre of normal
saline, what does that mean to you? It means
that you are distributing throughout the ECF.
What is the percentage or fraction of ECF
that you want to know for your boards and
wards right now? 1/4, 3/4.
That is it. Why even
worry about the ICF when you don't have to?
So be smart about how we study. Be smart about
how you apply the information and why would
you want to give normal saline in your patient
most likely? Who is that patient that was
coming into ER? Probably a patient that
was severely hypovolemic. Correct? So you're giving them one
litre of normal saline. Of this, you will
have 3/4, 1/4.
3/4 would be where? In the interstitium.
1/4 would be in your plasma. We have 750 and we
have 250. Of these two compartments in the
patient that came in with hypovolemia,
clinically what is your blood pressure? Decreased.
How would you then increase the blood pressure?
Which compartment is more important? The intravascular
space. So of these two values, 250 or 750,
what is the target? 250, right. The 250 is
what helped intravascular volume raise the
blood pressure. I hope that is clear and every
time that you go through IV fluids, as I said
it doesn't matter. For sure medical school
student or if you are a resident, your target,
your objective is well how much of my fluid
do I need to then get into my intravascular
space and then from there you can play around.
Now that you have normal saline, now things
become a little bit more complicated, I'll
walk you through this. Take a deep breath.
If you hate math, don't do that, don't hate anything in medicine
because then you automatically put up a barrier
and you end up providing resistance that is
not necessary. Your job is to reduce that resistance.
Can I have fun with you? Tell me as to what
decrease of resistance when you talk about
afterload, about TPR? So you are going to be
the alpha-1 antagonist. You are the syndrome,
my friend. So you are the praiser's sin who
is an alpha-1 antagonist removing the resistor
through all of your learning. So your afterload
decreases, my goodness gracious you are just
consuming this information. Let us take a
look at half-normal saline. 500 cc of this
is free water, what about this? It is going
to be distributed throughout total body water.
What about that 500 cc of normal saline? Well
that will be only in the ECF. Okay. Next step
let us deal with only right now, the 500. Pay
attention. What kind of water? Free water.
It will be distributed throughout total body
water. What does it predict? What those fractions
are? So this will make sense and this is how
you do your questions too. Any question that
you get you predict as to what you should
find in the answer choice so that you cut
down on wasting time. And if it is there fantastic
and if it is not, then maybe do a little bit
more thinking. But if you look for it first
in the answer choice, it might confuse you
further, especially when you get your answer
choice that will go A from K. That is a lot
of answer choices. I am not even joking total
body water. We are going to go through ECF and ICF,
2/3 will be where? ICF. 1/3 will
be ECF. So therefore for 500 cc, we will take
that third and that will then remain in your
ECF. What are you going to do next? What is
your objective? I told you. I now sound like a
broken record. What is your objective? It
is to see as to how much of the fluid you
get into your intravascular compartment or
your plasma. So you are going to take this
ECF into what with it? Further divided into
3/4 and 1/4, but not quite yet.
There is 167 of the 500. There is 333
of the 500, in the ICF. Let us let the ICF
go because that does not control blood pressure.
That is not what is clinically relevant right
now. We are still left with another 500 cc.
What about this? Normal saline. You tell me
the fraction that we can use here. 1/4, 3/4. Correct?
Which one are you paying attention to? 167, 1/4 will
remain in the intravascular space. Now how
do we get here? We took the 500 and we
divided this into your TBW with water and
then we took the 500 from normal saline and
then we take 3/4 and 1/4.
How in the world do we get 667 right now?
How did we get that? 500. Pay attention. That
500 cc of normal saline. What is it? Only
ECF. From the previous discussion, the water
that you are seeing appear, how much of that
free water was in the ECF? 167, good. Would
you tell me at this point with one litre of
half normal saline, how much of this is being
distributed in total in the ECF? 500 plus 167
gives you 667, and that is which you see here. The
667. Of the 667, what is the most important
objective? How much of this 667 got into your
plasma or intravascular space? Hence we get
167. Now this would be the most complicated
question that you will get as far as your
medical school is concerned. Even in residency
you will do this in your head and when attending
asks you, then you know exactly as to what
he is looking for. How much of this fluid
that you are giving? Whatever IV fluid that you
might be using is then entering the intravascular
space. Now just be to technical. We have the
rest of the 500 in the interstitial space,
whatever, there it is. Okay, but your objective
intravascular space. Got it? If you haven’t,
makes you review this real quick, you have
it, just no resistance, just be open to what
is happening here. Listen to every single
term that I said because it will then help
you to figure out the differences of free
water, ECF; ECF, intravascular space.