00:02
Acute hypoxia is where we are,
and/or should I say acute hypoxemia.
00:07
Right, we always have to be
a little bit more detailed.
00:09
It’s a V/Q mismatch,
improves with supplemental oxygen.
00:14
So, this, for example, gives you examples
such as pneumonia, COPD flares and PE.
00:20
Remember that no matter any time
during a disease course of your lungs
that supplemental
oxygen is given,
but you always have
to utilize caution
because of that condition that
we called your hypoxic drive.
00:37
But, if it’s COPD flares, then you are
left with really not much of an option.
00:44
Something that you
want to keep in mind
and something that you very
much want to understand
is the fact that what if
your alveoli was to collapse.
00:52
This brings us to ALI,
which stands for acute lung injury
or we have acute respiratory
distress syndrome.
01:00
What these have in common is the fact
that ultimately, the alveoli collapse.
01:05
And when your alveoli collapse,
they’re no longer functional.
01:09
This is called a
pulmonary shunt.
01:11
A shunt means that there is deoxygenated
blood passing in the systemic circulation.
01:17
You should be familiar with the
right-to-left shunting in the heart
that happens in cyanotic heart
diseases, such as Tetralogy of Fallot.
01:24
So, why would you be so familiar
with shunting in the heart
and you’re not so familiar
with the shunting in the lungs?
The only way that you can
get shunting of your blood
from the pulmonary
arterial side,
which has normally a
PO2 of approximately 40.
01:38
To get your PO2 of 40
to your pulmonary veins,
you shunt across an alveoli
that are no longer functional.
01:44
So, this is a intrapulmonary
type of shunt.
01:48
Now, if there is an
intrapulmonary type of shunt,
if you were to give
this patient oxygen,
if that alveoli are collapsed,
how should you get a significant response?
You don’t get one.
01:59
Now, the same thing can also be
applied to intracardiac shunt.
02:04
For example, say that you had a
right-to-left shunt at some point in time.
02:08
If you did, then you get deoxygenated blood
into your left side, from your right side.
02:14
So you’ve shunted your lung
and thus by giving oxygen,
are you having a
response that you expect?
No, you don't.
02:21
Look for that particular
clinical description.
02:27
What else may cause
acute hypoxemia?
PaO2 or the partial pressure
of oxygen inside the alveoli
can become low as is the
case at high elevations.
02:37
The reason for this is that the FiO2 or the
fraction of oxygen in the air we breathe
is effectively constant everywhere
on the planet around 0.2.
02:46
What changes at high altitudes
is the atmospheric pressure
or barometric pressure.
02:51
As you remember,
we find the partial pressure of oxygen
by multiplying the
barometric pressure
which we normally consider to
be 760 by the FiO2 which is 0.2.
03:02
At high altitudes, however, your alveoli
see a lower partial pressure of oxygen
because you're now multiplying a lower
barometric pressure by the same 0.2 factor.
03:12
This then translates into decreased oxygen
diffusion as the A-a gradient is decreased
and ultimately results in hypoxemia
and acute altitude sickness.
03:21
What else?
Impaired diffusion.
03:23
Now things become a
little bit easier.
03:24
What this basically
means is the fact
that you’re not able to
properly cross your barrier.
03:29
What barrier?
The barrier between the alveoli
and trying to get your oxygen
into your pulmonary capillary.
03:35
Impaired diffusion, couple of important
points that we already discussed.
03:38
A-a gradient widened or
normal, please?
Good, widened.
03:43
What are some things that you wanna
take in consideration for A-a gradient?
The age is a big one, right?
And the other big one is
the fact that if you were
to then increase your
FiO2 in hospital setting.
03:55
Okay.
03:55
Now, the other big point to
test is going to be DLCO.
04:01
Your DLCO laboratory examination
with the impaired diffusion
would find a decrease DLCO.
04:08
Hypoventilation
can cause hypoxia,
but this occurs with
(and due to) hypercapnea.
04:14
So, hypoventilation,
if there isn’t enough breathing,
please understand that you’re
having a decrease in oxygen,
but that you also end up having
an increase in carbon dioxide.
04:25
That’s not good.
That displaces everything.
04:27
Acute respiratory
failure is my issue.
04:29
We’ve walked through some important
points of acute hypoxemia.
04:33
Let’s continue.
04:35
Now, the five possible
physiologic causes of hypoxia.
04:38
Hypoxic respiratory failure
is almost always caused by
a V/Q imbalance or a shunt.
04:45
And by V/Q imbalance, we’re referring
to something like perfusion defect,
ventilation defect and dealing
with a diffusion defect in general.