So what's the difference between peak pressure and plateau pressure and why is it important? Let's go find out?
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So the pressure in your ventilator is comprised of two parts the resistive pressure and the elastic pressure
the resistive pressure is that which is encountered when air flow is pushed through the Airways the
Elastic pressure is that which inflates the lungs and the chest wall
So increasing ventilator pressures must be due to one more both of these if your patient's airway
Pressures are going up
There's either a problem with the resistive pressure or the elastic pressure
So let's talk about peak pressure and plateau pressure
so the peak pressure in the ventilator circuit is related to the resistive pressure and
Plateau pressure is related related to the elastic pressures, so let's look at this diagram to imagine
We're ventilating the lung and we can see here. The pressure. Curve as we do so
Point one where we're ventilating the lung and the airway pressure goes up
And you can see that the volume also
Increases at point two during expiration the pressure goes down and the flow moves in the opposite direction
as the air moves out so if we understand that the peak pressure is the
Maximum pressure in the proximal airway at the end of the inspiration we can see this at 0.4
0.5. We've instigated a breath hold which can easily be done by most modern ventilators through a simple press of a button
This is the equivalent of occluding the endotracheal tube at the end of an expiration when you do so the pressure
At the end of inspiration NOT expiration
Equalizes between the tube and the alveoli so consequently plateau pressure is a surrogate for end inspiratory
alveolar pressure
I think using the balloon analogy might be useful at this point imagine
You're blowing up a normal balloon as you inflate the balloon blowing quite hard this equates to the peak pressure
Imagine then that you stop blowing but keep the balloon in your mouth
the pressure then
Equalizes between your airway and inside the balloon this pressure will not need to be as high as when you are actually
Inflating the balloon and this for this therefore equates to plateau pressure
So peak pressure is dependent upon the resistance in the airways and also on the compliance of the lungs
If the airway resistance is high or the lungs have become stiff then the peak pressure will rise
The plateau pressure however is only related to the compliance of the lungs in other words how stiff those lungs are
Let's look quickly at these two examples in this example. You can see that
There is a high peak pressure if the difference between the peak pressure and the plateau pressure is greater than 5 millimeters of mercury
Then it is defined as an elevated peak pressure in the next diagram. You can see that
There is an elevated plateau pressure, so what can this tell us?
Well if we have a high peak pressure. There is possibly an airway issue for example
We may have a bronchospasm we train secretions mucus plug or the endotracheal tube
tip might be blocked or it might be sitting against the wall of the bronchus for example if
We have a high plateau pressure and remember. This is related to the compliance of the lung we may have a pneumothorax
pulmonary edema a RDS or a pneumonia
So if we can understand the difference between peak and plan so pressure we may be able to diagnose what's wrong with our patients
Ventilation and consequently what we might be able to do to improve it
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