00:01
Welcome back.
00:02
Thanks for joining me
on this discussion of
fluids and electrolytes
in the section of perioperative care.
00:09
Fluids and electrolytes are incredibly important
to maintain daily physiologic function,
but also it’s incredibly high yield
for standardized examinations.
00:19
So, I hope you're
paying close attention.
00:22
Let's start the discussion
by an estimation of total body water.
00:27
Total body water
when expressed in liters
is approximately two thirds
or 0.6 times your total body weight in kilograms.
00:36
For example,
a standard 70 kilo patient
would have approximately 42 liters of fluid.
00:42
That's a lot of fluid.
00:44
Now, the distribution of the
fluid is equally important.
00:48
The vast majority of that 42 liters of fluid
is actually intracellular
to the tune of two-thirds.
00:56
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.
01:08
When you do all the math,
you figure that 7% of your total
body weight is actually intravascular.
01:14
That's how we get the value
of approximately 5 liters of fluid
in your total circulating volume.
01:23
Our body does an amazing job of
maintaining intake and output homeostasis.
01:29
On a daily basis,
we approximately ingest 500 in –
or potentially excess
depending on how
much water you drink.
01:37
In our food,
we probably take in about 800 cc of fluid.
01:41
And normal cellular processes
contribute about 300 cc.
01:46
In our output,
we make about 500 cc of urine a day.
01:50
Our skin and insensible losses
account for approximately 500 cc.
01:55
Breathing alone,
because of the humidity,
loses about 400 cc.
01:59
And our stool,
although mostly without fluid,
still contains about 200 cc.
02:05
And that's an important point,
because patients with diarrhea
can lose fair amount of
fluid through their stools.
02:14
Electrolytes are incredibly important
and will be the focus of the
majority of this lecture module.
02:20
Remember, potassium is mostly intracellular.
02:24
If you forget that,
all you have to do is look at
standard chemistry laboratory values.
02:29
The potassium is rarely
ever greater than 4.
02:33
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.
02:45
Aldosterone increases sodium reabsorption
at the expense of excreting potassium.
02:53
This allows it to maintain electrical neutrality
because otherwise we would have entropy.
02:59
Potassium-sparing diuretics, however,
antagonize the action of aldosterone on potassium.