In this video we'll be discussing APRV mode of ventilation or airway pressure
release
ventilation
This mode is essentially used as a recruitment mode to improve oxygenation
especially in patients with ARDS
If you have this patient who has ARDS and he is already placed on
Volume controlled mode of ventilation
with tidal volume of
420, flow of 30 liters per minute,
extended inspiratory time of
1.9. Seconds at a rate of 12 per minute
and
PEEP of 12 centimeter of water
Now in order to make the change or the switch between
Volume control mode of ventilation and
APRV, You need to notice
What is the mean airway pressure provided with this mode of ventilation and can take a look on this
Number here, it is 25 centimeter of water as a mean airway pressure
So we'll take this
to start our settings for APRV and we add
Five more centimeter of water to define. What is the starting
P high for the patient, so we'll start at
30
Centimeter of water, and then we'll decide for how long this 30 centimeter
of water will be
kept in inspiration and
We can say four to five seconds
Maybe six seconds, so we'll give extended inspiration, so let's define it here at five seconds
and
then we'll decide about the expiratory pressure or the
P low,. The P low will be
Zero to release that pressure all the way to zero and we'll define the expiratory time or the T low
at 0.9 second
and let's start and see what we have so P high of 30
centimeter of water
P low
Zero that means the pressure goes up to a 30 centimeter
And then is released to zero. The inspiratory time or the T high is five
seconds and the expiratory time or the T low or the release time is
0.9. Second
Now this way you can see that the
Pressure goes up from zero to 30
centimeter of water at 0.2 second, which is the ramp, inspiratory flow follows and
volume goes into the lungs
this
volume stays into the lung for the duration of
inspiration and the flow reaches here zero the patient can
breath on top of this pressure, and
Then after five seconds the pressure is released all the way to zero and the patient exhales
Now notice that every time the patient is
Exhaling or that pressure is released the flow goes to the peak expiratory
flow and then decelerates, but notice that in this patient
Here the flow goes goes up to zero
That means every time that pressure is released the patient is derecruiting
So you don't have any PEEP on this patient and every time you release that pressure the flow goes all the way to zero
So that means you empty the lungs completely!
from the air and
You live in the the lungs derecruited, so this is something that a lot of
Operators make as a mistake and in order to correct this you need to cut that
Expiratory flow at a value of 40 to 70 percent of the peak expiratory flow so allowing
persistent expiration
at end,
persistent flow at the end of expiration
Persistent flow at the end of expiration which is Auto PEEPing so you do not derecruit the lungs, so
in order to do this we need to go down on the
T low will go down to 0.7 first and see what we have, so with 0.7
seconds of T law were able to cut the
Expiratory flow at a value it looks like around 20 percent of the peak expiratory flow
So that's not enough because
Auto-peep provided what this would be minimal. Of course this is all only an estimation and
We'll go to 0.5 and see what happens point five seconds, so
Now with 0.5 second of T low
the expiratory flow is cut almost at forty to fifty percent of the big expiratory flow
So now I'm more confident that the lungs are kept
Recruited so were not so emptied the air outside the lung in every exploration
so in this mode if we define the phase variables and the control variables of
each breath the control is
pressure as a machine is intended to deliver the
P high
But the trigger for that control delivery is time, every
Five and a half seconds will be a breath which is actually the
T high plus the T low, so the T high is five seconds and the T low is 0.5 second
every 5.5 seconds
There will be a breath
So the trigger his time the control is
pressure, and the cycle changing from inspiration to expression or the release is
also time, after five seconds
The patient can breathe anytime here above that peak pressure
And
if the patient
started to breathe will be his own tidal volume above that pressure you
Can see here how the patient got
Got some flow here and increased a tidal volume above what is already delivered to the patient
So this is a brief description of APRV, how to set it
and how to maintain it
If the patient started to get better and you want to wean, you can use this mode as a weaning mode and
Essentially what you do is you extend the inspiratory time
And you decrease the P high gradually to convert this mode
into a
CPAP mode of ventilation
Thank you