Thanks for joining me
on this discussion of
fluids and electrolytes
in the section of perioperative care.
Fluids and electrolytes are incredibly important
to maintain daily physiologic function,
but also it’s incredibly high yield
for standardized examinations.
So, I hope you're
paying close attention.
Let's start the discussion
by an estimation of total body water.
Total body water
when expressed in liters
is approximately two thirds
or 0.6 times your total body weight in kilograms.
a standard 70 kilo patient
would have approximately 42 liters of fluid.
That's a lot of fluid.
Now, the distribution of the
fluid is equally important.
The vast majority of that 42 liters of fluid
is actually intracellular
to the tune of two-thirds.
One-third of your total body water
is actually extracellular
and only a very small percentage
one-third of one-third is contained
in your intravascular or circulating volume.
When you do all the math,
you figure that 7% of your total
body weight is actually intravascular.
That's how we get the value
of approximately 5 liters of fluid
in your total circulating volume.
Our body does an amazing job of
maintaining intake and output homeostasis.
On a daily basis,
we approximately ingest 500 in –
or potentially excess
depending on how
much water you drink.
In our food,
we probably take in about 800 cc of fluid.
And normal cellular processes
contribute about 300 cc.
In our output,
we make about 500 cc of urine a day.
Our skin and insensible losses
account for approximately 500 cc.
because of the humidity,
loses about 400 cc.
And our stool,
although mostly without fluid,
still contains about 200 cc.
And that's an important point,
because patients with diarrhea
can lose fair amount of
fluid through their stools.
Electrolytes are incredibly important
and will be the focus of the
majority of this lecture module.
Remember, potassium is mostly intracellular.
If you forget that,
all you have to do is look at
standard chemistry laboratory values.
The potassium is rarely
ever greater than 4.
Aldosterone is a very important –
has a very important mechanism
in the distal collecting system
to maintain not only fluid homeostasis,
but affect the potassium channels.
Aldosterone increases sodium reabsorption
at the expense of excreting potassium.
This allows it to maintain electrical neutrality
because otherwise we would have entropy.
Potassium-sparing diuretics, however,
antagonize the action of aldosterone on potassium.