Now, all that I wish to do here is introduce
the terms here. And then in the next topic,
we’ll go into definitely what the modes
will look like with the graph and how to interpret
your graphs based on the type of mode of ventilation
that you wish to provide. We’ll have assisted
control, we’ll have what’s called intermittent
and then pressure control.
FiO2, what does that mean? Good. Are you picturing
this? FiO2, the prime example that I’ve
given you over and over again is high altitude.
Why does FiO2 drop there? Because of barometric
pressure. In a hospital setting, what might
you wanna do with FiO2? Literally, the parameter
that you can change.
Tidal volume and respiratory rate. I just
went through a table to clearly highlight
those two patients of rapid shallow breathing
versus rapid deep breathing. You tell
me, what’s more important to increase your
alveolar ventilation, which is the objective?
Very good. It’s your tidal volume, isn’t
it? Because you want to make that
dead space as negligible as possible. So,
therefore, by increasing tidal volume and
we’re going through rapid deep breathing
there, as a compensation for DKA. But,
understand though, clinically speaking, the
respiratory rate and also increasing tidal
volume will then give you a profound increase
in your alveolar ventilation. Are you seeing it?
If you don’t, go back to discussion,
please, about our alveolar ventilation.
And then, we have positive end expiratory
pressure. I’ll show you a graph here that
will quickly show you what the difference is in terms of breathing with
a positive pressure versus a normal,
negative pressure. Let’s take a look.
Here, we have a graph explaining two patients
that are receiving, well, PEEP specifically,
but then patient B has PEEP + 8 cm of water
that he or she is receiving. We’re gonna
walk through this so that you clearly see
the advantages of PEEP itself and then understand
as to what some of these important disadvantages
We have patient A in orange. The X-axis then
represents the breathing rates or rhythms
and the Y-axis then represents the pressure.
Let us now begin at FRC. What does FRC mean
to you? It’s ground 0. Here, for patient A,
literally is 0. But theoretically, don’t
try this at home, it’s your epiglottis being
open with no air moving in or out. That’s
the definition of FRC. So, this is a functional
residual capacity. Zip.
Okay, so, now, you’re gonna begin breathing.
Now, upon breathing, you’re gonna have inspiration
that’s taking place that takes you to
the increase in spike. And at the end of expiration
then, obviously, alveoli becomes smaller.
But this is dangerous. Say that you have a
patient who requires oxygen is in a state
of respiratory compromised and your patient
is at risk for, guess what? Atelectasis. What
might you want to do to make sure that alveoli,
because, remember, if that alveoli shuts,
that surfactant has a really hard time
protecting the alveoli from maintaining or
trying to keep open. So, therefore, the more,
remember, and this is once again that the
normal stuff that you wanna know. If it’s
surfactant, it protects whom better? An open
alveoli. It protects a smaller alveoli even
a little bit better, doesn’t it? Because
that’s what requires the decrease in surface
tension. Surfactant, amazing name actually.
And so, therefore, you wanna at least keep
that alveoli alive and open, so that things
do not collapse. Is the objective understood?
Let us now take a look at patient B.
So, normally speaking, how was it that you
open up your alveoli? Inspiration, pleural
pressure becomes more negative. The more that
the lung becomes negative, what happens to
the alveoli? Ah, it expands. But now, you
are going to become the lung. You, the clinician.
You’re going to become a mechanical lung.
So, therefore, how do you keep that? How do
you keep that alveoli open? You have to introduce
positive pressure into the airways.
So, you introduce positive pressure, along
with it, well, you have it at 8 cm of water.
That’s quite a bit of pressure, can you
imagine? And with that positive pressure,
you then maintain even at the end. So, I want
you to come down where it says positive PEEP.
It stands for positive end expiratory pressure.
So, at the end of expiration, there’s still
positive pressure that is then maintaining
the patency of the alveoli. And you noticed
that here, even at the end, we’re still
as high as +8. That’s a lot of positive
pressure in your alveoli to keep it open.
Is that clear? Completely the opposite of
what? Negative, normal.
So, now, what are some of the major disadvantages
that you’re worried about? Well, the major
disadvantage of PEEP is the fact that you
might introduce so much positive pressure,
you might then cause compression of the pulmonary
capillaries because they’re right there.
That membrane is so small of the alveoli,
right across the street is whom? The pulmonary
capillary. And so, therefore, think of it as being an avalanche.
Think of a tiny road and there is all those
rocks falling. It completely obstructs the
road and the road no longer, well, there’s
no cars moving. In other words, there’s
no blood moving, same thing. So, that alveoli
is at this point introduced positive pressure,
exerts the effect across the street or on
the street which then represents the blood
vessel and gone is the blood vessel, right?
Wow, if the pulmonary capillaries
are now, well, obstructed, who is going to
fill the effects? Good. The right side. May
result in right ventricular type of failure.
is that clear? So, understand in the
long run, what kind of effects that you wanna
use or exercise caution with when utilising
tools such as positive end expiratory pressure.