The High Frequency Oscillatory Ventilator, by Dr. John Arnold.
Please note that, in this video, we will be following the guidelines used at Boston Children's
Hospital.
Some of this information may need to be modified based on the equipment, guidelines, and practices
in place in your institution.
I'd like to take several minutes to demystify this device.
This is a high-frequency oscillatory ventilator, as you know.
This is the Sensormedics 3100A.
And, when initially confronted with this device in the ICU setting, many people are confused.
Let me help.
This is simple.
This is the mean airway pressure.
And you're familiar with that number from conventional ventilation.
And this is the amplitude.
This is the delta pressure, measured proximately in the ventilator circuit.
These are really the only two numbers you need to concern yourself with.
When we transition to high frequency, almost all patients are on 100% oxygen.
We typically will pick a frequency based on the patient's size.
In Samantha-- a 13 month old, roughly eight-kilogram child-- we're going to pick a frequency of
10 Hertz.
And virtually all of our patients are managed with an I:E ratio of 1:2, giving a percent
inspiratory time of 33%.
So we're going to ignore these two numbers and focus on these two.
So as you know, when we transition to high frequency, we'll typically transition at a
mean airway pressure five to eight sonometers higher than we were on conventional.
And one typically sets up the ventilator prior to transition.
Now, you can increase the mean airway pressure knob in one of two ways.
You can adjust mean airway pressure by manipulating the size of the orafice on the expiratory
limb, which is what I do when I manipulate this knob.
So I'm increasing mean airway pressure.
And I'm decreasing mean airway pressure.
And the other way to manipulate mean airway pressure is to increase the flow through the
circuit through that fixed orafice.
And that's called the bias flow.
And we can do that by manipulating this knob.
All patients need to start with a bias flow of 20 liters per minute.
Occasionally, when you've increased mean airway pressure maximally by closing the orifice,
you will need to increase the bias flow to further increase the mean.
So I'm going to now increase the bias flow from 20 to 25 to 30 liters per minute.
And look what it's done to the mean airway pressure.
It's increased it dramatically.
Let me go back to 20, and you'll see that in reverse-- 25 and 20.
So that's mean airway pressure.
Now the delta pressure is displayed here.
It turns out we adjust the delta pressure by turning the power knob.
So you actually increase power.
And that generates a higher delta pressure, which is a measured variable.
And we increase power simply by turning this knob.
So I'm now aiming to increase the Delta P to 60 by increasing power.
The Delta P is the peak-to-trough pressure, again measured proximally in the ventilator
circuit.
And to increase it further to 65, we simply increase power in another increment.
So, it's a very simple device.
The conventional ventilator is complicated, this is not.
We focus on mean airway pressure and delta pressure.
I hope that was helpful.
That concludes our video on the high frequency oscillatory ventilator.
Thank you.
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