00:01
Okay, so let's turn back
to hemodialysis.
00:04
So let's talk about how solutes are
transported across that dialyzer.
00:09
I want you to remember
what we're talking about again.
00:11
In hemodialysis,
I essentially have a patient
hooked up to a dialysis machine,
blood is going to be coming
from that patient going through
an extracorporeal circuit,
it goes through the dialyzer.
00:22
That dialyzer is separated by
a semipermeable membrane
on the other side or
other compartment of that dialyzer
is something called
dialysate,
that's dialysis solution.
00:32
And it contains,
essentially, what I want my
patients blood to look like.
00:37
A sodium concentration of typically
around 137 mL equivalents
Calcium closer to 10.
00:43
I want that potassium
if they have high potassium
in their blood to be low,
and then bicarb to be high,
because my patients
remember are
not being able to essentially
get rid of the acid production
that they make every day.
00:57
So that is then separated by that
semipermeable membrane.
01:00
The blood flow and
the dialysate flow
go counter current
to each other,
the blood is then returned back
to the patient
through their dialysis catheter,
or through their vascular access.
01:12
So the mechanism by which
we do solute transport release
is going to depend
on diffusion.
01:18
And that again, is going to depend
on that semipermeable membrane.
01:21
How porous are those
holes essentially,
in that semipermeable membrane,
It's going to depend on the
molecular weight of the solute.
01:29
How big is that solute?
Something like urea,
which is so tiny,
can easily diffuse
across that membrane.
01:35
But something bigger,
might take a lot longer
phosphorous or creatinine
might take a little bit more time
to dialyze across
that membrane.
01:42
Certainly things like
beta-2 microglobulin
or bigger molecules
like the aliphatic amines
are going to be more
time dependent,
and will take time to go across
that membrane.
01:52
Also the speed with which
these are passing each other.
01:55
So if I have a very high blood flow
in my patient
flowing across that membrane,
and a very high dialysis flow
moving counter current to that,
that's also really going to increase
my diffusive efficacy.
02:08
I also depend a little bit
when I'm talking about
solute transport on
ultrafiltration.
02:13
So ultra filtration is essentially
applying a negative pressure,
a negative hydrostatic pressure
on that dialyzer.
02:21
And by doing so,
I'm able to pull out water
from that blood volume.
02:25
When I do that,
the more ultrafiltration
or the more
the hydrostatic pressure,
then I actually can drag out solute
as well by solvent drag.
02:35
That's also the mechanism
of volume removal
that I'm talking about
are ultrafiltration.
02:40
So again, our patients are coming in
not only with the solutes
that need to be essentially cleared,
they also have excess volume.
02:48
They're edematous.
02:49
They have they're retaining
sodium and water.
02:52
So the best way to remove that
is to apply that negative pressure
or hydrostatic pressure
to that dialyzer
thereby removing water,
and then with that
by solvent drag,
we have sodium removal
as well.
03:06
In peritoneal dialysis,
I'm actually going to use that
peritoneum as my dialyzer.
03:13
So that's my
semipermeable membrane.
03:16
So essentially my dialysis fluid is
going to be in different volumes.
03:22
So I can have either
liters or five liter bags
depending on my patient,
whether they're going to do
ambulatory dialysis,
that's the manual
type of dialysis
or the kind where they hook up
to a machine.
03:34
The sodium concentration is
typically around 132.
03:38
Potassium,
oftentimes is zero
in my dialysis solution
for peritoneal dialysis.
03:42
So I have to be really
cognizant of that.
03:45
My patients on PD
or peritoneal dialysis
oftentimes can become
hypokalemic
and it's not uncommon
to see those patients
taking potassium supplements.
03:55
We also have a glucose
or dextrose concentration
in our
peritoneal dialysis solution.
04:00
Now, reason being is that
we're actually
going to take advantage
of the osmotic gradient
that can build
to cause ultrafiltration.
04:08
We've got a calcium
that's typical to the blood calcium,
magnesium,
and we're going to use lactate
as our source of essential base.
04:16
in order to provide the base needed
from the acid production
that these patients make every day.
04:22
So the mechanism of solute transport
is the same,
it's diffusion,
just as we talked about,
and ultrafiltration, depending on
how much ultrafiltration we get.
04:30
You get a little bit of convective
transport with that as well.
04:34
The mechanism of volume removal
is going to be through
ultrafiltration,
but instead of applying
a negative hydrostatic pressure,
I actually can use
that osmotic gradient
that I'm creating by
putting a dextrose solution
in that peritoneal
dialysis solution.
04:49
So if I have a very high dextrose
of 4.25% or 2.5%,
that's going to stimulate
water movement
from the blood side
to that cavity
and with that I will have
solvent drag including sodium.
05:03
And that's the way
I can remove volume.
05:06
So when we're taking care
of these patients,
there's a few aspects that are
really important to pay attention
because it's going to influence
the morbidity and mortality
of this patient population.
05:15
Number one,
when I'm doing these therapies,
I have to make sure that I'm
actually adequately removing solute.
05:21
So there's mechanisms
that we can do that
by looking at urea and
the clearance of urea,
we can see how adequately
we're moving solute
across those membranes
that we're talking about.
05:31
Now remember, urea isn't one of
those uremic toxins,
but it's something that we can use
to look at the transport
of how efficaciously
we're transporting solute
across membranes.
05:42
We also want to look at the
adequacy of blood pressure control
and in particular,
the patient's volume status.
05:49
We really try to maintain a
patient's dry weight,
that means the weight
at which they don't have
extra volume on their body.
05:55
So it's critical
in order to make sure
that you have appropriate
ultrafiltration,
removal of salt and water,
that will absolutely influence the
patient's morbidity and mortality.
06:04
We want to manage
the patient's anemia.
06:07
Remember, patients who have
chronic kidney disease
and end-stage renal disease,
lose those specialized fibroblasts,
which make a erythropoietin.
06:14
That's responsible for generating
red blood cells in the bone marrow.
06:18
Without that,
they become extremely anemic.
06:20
So most of our patients on dialysis
are on Erythrocyte Stimulating Agent
(ESA)
in order to correct their anemia.
06:28
Our patient also,
it's very important to pay attention
to their protein nutrition.
06:34
We actually encourage our patients
to eat very high protein meals.
06:37
And I want to make
a point about this
because in our
chronic kidney disease lecture,
we actually talked about
how we want patients
to actually restrict protein,
that high protein can actually
progress their disease.
06:48
But once the patient is on dialysis,
they're so catabolic.
06:52
They have protein energy wasting,
and it's critical for them
to replete that.
06:56
So they must have
high protein levels.
06:58
We actually tell patients
to eat somewhere around
1.5 grams per kilogram
of protein per day.
07:04
So that's quite a bit.
07:06
We want to control their
hyperkalemia.
07:08
Again, these patients
don't have a mechanism
of getting rid of their
potassium
so it's important to dialyze them
against low-potassium bass
and ensure that
they're eating correctly
in low potassium foods.
07:18
And we want to manage
the renal bone disease.
07:20
This is things like
hyperparathyroidism and vitamin D.