On this topic of acute respiratory distress
syndrome, students have a hard time figuring
out what exactly caused the collapse of the
Let’s begin. What is ARDS? It used to
be, once upon a time, may be called Adult
Respiratory Distress Syndrome, but you can
no longer do that because it’s very possible
that you might find the causes that we will see
here commonly for ARDS including sepsis that
might also take place in children. A clinical
manifestation of a diffuse alveolar damage.
The operative word here is alveoli in which it
gets damaged. Then what
happens? It disappears. It collapses. Results
in atelectasis. What does that mean to you
in terms of pathophysiology? Is this a dead
space or is this a shunt? This is going to
be a pulmonary shunt. You will see as to how
that become important for us as we move further
into our lecture. Diffuse alveolar damage
is the final common pathway for a variety
of insults to the lung. So, therefore, let’s
say that your patient is suffering from a
sepsis or septicaemia and that the patient went
from having a pneumonia or perhaps even aspiration
and there is so much damage that has taken
place to the lung and alveoli, resulted
in diffuse alveolar damage. We have acute
respiratory distress syndrome. Now, this mostly
does occur in adults, you can say that. And
the only thing is that you need to keep in
mind that could insults such as these also
affect children? Sure it can. Toxic inhalation,
drowning, all of this is then going to cause
severe damage to the alveoli resulting in
what? Diffuse alveolar damage. Welcome to
acute respiratory distress syndrome which
is then going to manifest as a pulmonary shunt.
The clinical manifestations of diffuse alveolar
damage can be seen in systemic or non-pulmonary.
So, from this, let’s take a look at other
important causes. Sepsis is probably the most
common cause of acute respiratory distress
syndrome. At some point, we will then transition
into a more specific neonatal respiratory
distress syndrome in which the most common
cause there, well, we will walk through, but
one of it, of course, being premie, meaning
to say premature baby.
Next, pancreatitis, trauma and burns. Anyone
of those actually could result in a condition
called third spacing as well. For example,
pancreatitis and burns are big ones. How many
compartments do you have in your total body
water? Two major compartments - ICF and ECF.
The fluid should be remaining in one of those
two compartments. What if you pathologically
then introduce a third compartment? Really?
You can do that? Yeah, you can. If your patient
is suffering from pain. Where? Oh, here doc.
In my stomach. Anywhere else? Yeah, it actually
hurts in my back too. Hmm, well high in your
differential and then you find your lipase to
be elevated, you have pancreatitis. And pancreatitis
causes what? Well, at some point, you could
then accumulate fluid in third compartment
that has been introduced pathologically and
your patient will have hypotension. In addition
with pancreatitis, what are you looking for?
Oh, lipase. What are some of those other important
exocrine enzymes of the pancreas? They include
your trypsin, chymotrypsin, elastase, lipase,
amylase. All of those are what? Exocrine pancreatic
enzymes. Having fun yet? All these enzymes
might do what? Uh-oh, they might enter the
blood stream, might go up into lungs and then
may bring about damage. Welcome to ARDS. Fascinating.
Trauma, burns, all of these could result in
acute respiratory distress syndrome. So, severe
pneumonia we talked about, may be inhalation
of toxic and such, but understand, the most
common is the fact that you’ll go into sepsis.
Idiopathic known as Haman-Rich syndrome,
if you must memorise.
Acute respiratory distress syndrome results
in hypoxic respiratory failure. There is going
to be a significant V/Q mismatch. What does
that mean? Well, I began by saying that there
is going to be a pulmonary shunt, no doubt.
What does that actually mean to you, clinically?
Meaning to say that your patient is receiving
oxygen, but you do not find significant improvement
of this hypoxemia. Fascinating. Why? Because
the alveoli is gone, it ain’t there, it’s
collapsed. That's the significance, clinically,
of your pulmonary shunt, but you knew that
already and is it possible that you might
be introducing pathologic areas of dead space
units? Yes you may, yes you may. But the
main thing here is pulmonary shunt. In addition,
well now that you have damage taken place
to the lungs, you tell me, what does it say?
Cardiac type of damage or cardiogenic type
of damage to your lung or was it a noncardiogenic
type of damage to your lung? Obviously, a
noncardiogenic. What does that mean? I had
damage. What is the most common cause? Well,
maybe sepsis, maybe aspiration, what have
you. And if there is damage taking place in
acute nature to the lung, understand that
now, I am going to have an acute inflammatory response.
Okay. That acute inflammatory response
tumor, calor, rubor, swelling. So, therefore,
I have increased capillary permeability;Tumor -
swelling. Rubor – redness, calor - heat
dissemination. Obviously, you are not going
to feel the heat, but inflammation is taking
place and endothelial cells are then going
to then space out and then you have increased
capillary permeability. So therefore you
tell me, what kind of fluid? Protein rich
or protein poor? Good. Protein rich. Welcome
to exudate. This in turn leads to stiffening
of the lung and decreased compliance and the
more that you have leakage of fluid and its
exudate in the interstitium, you can only
imagine that the lung has now lost the ability
to do what? Distend. Welcome to non-compliance.
What are we looking at here in the chest X
ray? You will notice especially on the right
side of the chest, that you find quite a bit
of opacity there. That is because of the alveoli,
in fact, is dead but, I would have to tell
you this. As a medical student perhaps or
if there is lack of exposure to chest X-rays,
looking at this, well, all you know is that
there is increased opacity, you definitely
do not find calcifications here and the fact
that you find the issue taking place at interstitium,
hmm, tells you that is interstitial lung disease.
I mean to say that it seems like it is interstitium.
The alveoli, if they are dying, they are going
to appear getting a little bit more opaque. And
so therefore, you might get a chest X-ray
in which it is going to focus on the fact
that the alveoli is then being collapsed.
But, always go back to make sure that your
history coordinates with
the findings of your image. Remember, these
things you just use to complement your diagnosis.
Let’s take a look at important differential
diagnosis for you in ARDS. Pulmonary edema.