Protective ventilation tool or PV tool is available on Hamilton G5 and is used
to determine the optimal PEEP for ARDS patient and determine the plateau
pressure that should not be exceeded. In order to do that you click on tools and
then PV tool.. of course the patient should not breathing meaning that he should
be well-sedated and possibly paralyzed, the tool is not available in spontaneous
modes such as pressure support mode of ventilation or CPAP
Once you click OK you get into this window and you can see that you can give
one breath, you can define the starting pressure which is starting PEEP for the
patient, and let's just say that this is going to start from PEEP of 5 and we're
going to go from PEEP of five all the way to the top pressure which is the
peak inspiratory pressure of 35 and we'll do that at a ramp speed of
three centimeter of water per second that means it will take 10 seconds to
get from 5 to 35, once we get to this pressure will go down back to the PEEP at
the same rate of 3 centimeters of water per second, we will not put any pause here
once we click start here the pressure will start going up from 5 to
35 and then will go down back to 5. What we'll see here
here on the Left graph: what happens with the pressure versus volume
the pressure is on the x-axis and the volume is on the y-axis
so let's get this to start, and maneuver now is in progress, you will see that the
pressure starts to go up here, as the pressure starts to go up, the pressure
moves on the x-axis and once the volume starts to get into the lung we can see
that reflected on the y-axis. So the maneuver now is finished, so we can
analyze the graph, this is the pressure-volume curve and we can easily
identify three areas of different slopes, so you can see this is the first segment
that has a very shallow slope compared to the second segment here and then the
third segment. So let's identify these segments using the cursors, and we have
the first cursor, here once we move this cursor we can read the change in the
pressure with the change of the volume. The green is the inspiratory limp of the
curve and the yellow is the expiratory limb. Let's just concentrate on the Green
limb of the curve. For a pressure of 5.2 which is the PEEP which we have
zero volume, as we go up on the pressure you can see how the volume started to go up
so this is a pressure of 10 we get 21 ml of air into the lung
so we'll leave that cursor at the PEEP level and we will get the second cursor down all the way to an
area here where we think that there is a change in the slope of the curve
so I think it's going to be in this area here, so I will get the cursor all the way down to this area
so you can see at this point here the second cursor is reading the
tidal volume of 45 ml and a pressure of 12.8. So now we can
compare the second cursor with the first cursor readings and you can see we have
a change of volume of 45 minus 0 divided by a change in the pressure of almost 13
centimeters water of minus 5. So the change of volume divided by the change
of pressure defines the compliance for this segment here. We can see that the
compliance is calculated for us here and it is about 6, so this is a very low
compliance for this segment for this segment. So now we can look at the second
segment that has a better slope, so we'll get the second cursor all the way to the
higher point which is the upper inflection point, so I think it is going
to be at this point here, so we can set the cursor at this point and you can see
the tidal volume is 344 and the pressure is around 27 and the second or the first
cursor will move it back to the lower inflection point that was at this point here
Now what you can see is we have this segment here and these two cursors
are reading for me the change of volume divided by the change of the pressure
and that is associated with a compliance of 21 much better compared to the
initial compliance, so this segment has a better compliance than this segment and
it is defined by two points the lower inflection point and the upper
inflection point. Now you can notice that there is a
third segment here, and let me get the first cursor to the upper inflection
point and move the second cursor all the way to the right, now I can define again the compliance of..
I can calculate the compliance of this segment which is around 11
Notice that it is it has a lower compliance compared to the middle segment
so by taking this cursors back to the lower inflection point
and this one to the upper inflection point, we can see that if we ventilate our patient
between the lower inflection point and the upper
inflection point. we will benefit the most out of our pressure that we put since
this area has a better compliance than the initial area
meaning that if we go down lower than inflection point
we will end up with derecruitment of the lung and collapse of the alveoli
so you really want to make sure that the pressure does not go lower than this
lower inflection point, in order to do that we define the PEEP a 2 centimeters
of water above the lower inflection point, meaning that my PEEP should be
set at 14 or 15 for this patient. At the same time looking at the upper
inflection point here, if I go up and under pressure higher than 27
I end up gaining little of tidal volume, so that tidal volume which is not much is going
to be on the expense of higher pressure which might be injurious to the lung.
So I need to avoid going above the higher inflection point
so my patient should be ventilated between PEEP of 15 and plateau
pressure of 27 or maximum 28 that will give you a driving pressure of
28 - 15 that would be adriving pressure of 13 and that would be optimal for your
patient with ARDS.
This tool can be used also to recruit along and we will do that in a separate video
Thank you