00:01
Now we're going to take a look
at how you measure the ions
and fluid compartments.
00:06
In the US, we oftentimes
use something like
a basic metabolic panel,
This involves
eight different substances,
sodium, potassium, chloride, bicarb,
calcium, glucose, blood urea nitrogen,
and creatinine.
00:24
If you want to get a little bit
more expanded panel,
you can get other things like
the total protein concentration,
and albumin.
00:32
These are all very important aspects
to get a good feel
for what are the ions,
the osmolality potential,
as well as the
osmotic potential.
00:43
If you want to measure
osmolality directly,
you have to put it into a machine.
00:48
We do that with either
a freeze point depression
or a vapor depression.
00:52
If you don't have those available
and only have the chem-7,
you can calculate it.
00:58
And this calculation is just done
by this formula.
01:01
You take two times
the sodium concentration,
glucose divided by 18,
and the blood urea nitrogen
divided by 2.8.
01:09
So I provide you just an example
here at the bottom.
01:12
These are very typical
sodium values of a 140
glucose value of
80 milligrams per deciliter,
and a BUN of
8 milligrams per deciliter.
01:23
If you go through the formula,
it comes out to be
287 milliosmoles.
01:28
And this is a very typical
blood value.
01:31
So the interstitium and the blood
will be a right around this
285 to 287.
01:37
The intracellular component
isn't just a teeny bit higher,
maybe around 300 milliosmoles.
01:42
So this is what is going to be
circulating around in the body,
in comparison now
to what is within a cell.
01:49
We don't really know
what cell osmolality is
on a minute to minute basis,
because we don't really
puncture the cell
to measure its
fluid concentration.
01:59
We only measure what's in the blood.
02:01
And that is why measuring
blood levels of various substances
is very important for us clinically.
02:09
Now, what else is important
besides the osmolality,
and that is the oncotic pressure.
02:16
So oncotic pressures
help us to determine
if we're going to move fluid
into a blood vessel,
or it's going to be moved
out of the blood vessel.
02:24
And this is based upon proteins.
02:26
So we have the
total protein concentration,
the albumin,
which is the major component
of a serum protein analysis.
02:36
We have a few globulins
that are present,
but these are more minor
in nature.
02:40
So we lose the look at
total protein and albumin
as our primary factors
to determine the oncotic pressure.
02:47
Another important measurement
for body fluid balance
is the hematocrit.
02:53
When a person measures
the hematocrit,
they basically take whole blood.
02:58
You spin it down in a centrifuge
and it breaks out into three layers.
03:03
The first layer
is the plasma component.
03:05
And that is where of course,
we found the plasma proteins
that we just discussed.
03:10
There's also a Buffy layer.
03:12
And this Buffy coat is
white blood cells and platelets.
03:18
There is also a
red blood cell component,
and that is what makes up
the hematocrit.
03:23
So if you take the percent
of the red blood cells,
or the red blood cell component,
divided by the total,
you will get a percent number.
03:32
Now how do we use this particular
percent number
in body fluid balance?
The most important thing
to think about here
is that we still have our same
plasma component,
our Buffy coat,
and our hematocrit.
03:48
Her hematocrit, though,
is really packed red blood cells.
03:52
So if you think about
there's a certain number
of red blood cells present.
03:57
If you have cell swelling occurring
of the red blood cells,
such as if you put the blood
into a hypo-osmotic solution,
they will increase their size.
04:12
If they increase their size,
even though the number of
red blood cells haven't changed,
it will accomplish more of the total
and therefore have a higher
hematocrit.
04:25
The same number
of red blood cells,
if in a hyperosmotic solution
will shrink.
04:33
And if they shrink,
even though there's a same number
of red blood cells,
they will have less height
than the total height
and therefore it will look like
there's a decrease
in the hematocrit.
04:46
So both conditions,
the red blood cell number
has not changed
just if they have swollen,
or shrunk
and that will affect
the hematocrit.
04:59
When you think about what is a
hypo and a hyper osmotic solution,
think of it as the blood.
05:06
If the blood becomes hypo-osmotic,
it has a tendency to change
the hematocrit
by swelling
the red blood cells.
05:16
If you're in a hyperosmotic
condition of the blood,
your red blood cells
will tend to shrink,
and therefore, your hematocrit
will decrease.
05:27
So by knowing the plasma proteins
and the hematocrit,
we can get a really good idea of
where the water might be moving.
05:36
And this will help us to describe
the various challenges
to body fluid balance.
05:44
Now that we have our ions
being measured,
we were able to
measure our osmolality
and measure our oncotic pressures,
how do you determine how much is in
each fluid compartment?
Some of these fluid compartments
we can directly measure
and other ones
we have to calculate.
06:00
So let's go through the first one,
which is probably the most important
which is plasma volume.
06:05
For plasma volume,
we can directly measure this
by radioactively tagging albumin,
or we can tag it with a dye
such as Evans blue dye.
06:15
Then we look at its concentration
to determine the plasma volume.
06:20
We can also measure
extracellular fluid volume
by looking at another
radioactive dye with sodium,
or we can give a substance
like inulin or mannitol.
06:29
And we look at its concentration.
06:32
We can't directly measure
interstitial fluid volumes,
but we can use
is back calculate it
from the extracellular
fluid compartment
minus the plasma volume.
06:43
Finally, we can measure
total body water.
06:46
And this is done also
through nuclear medicine
and where you radioactively
tag water.
06:51
And this can be been measured
over time
to see someone's
total water clearance.
06:57
Once you have this
particular measurement
and the extracellular
fluid compartment,
you can use that to calculate
the intracellular fluid
by taking the total body water minus
the extracellular fluid volume.
07:10
And this gives us your
intracellular fluid.
07:13
Because again,
you cannot directly measure
intracellular fluid.