SUSAN WILCOX: This video will cover ventilation in obstructive lung
disease.
Obstructive lung disease comes in several different formats,
and many of these have overlapping presentations.
The first one is asthma.
The key feature of asthma, of course, is that it is reversible.
So patients can have bronchospasm, but it will reverse
with appropriate medical therapy.
Chronic bronchitis, conversely, is not necessarily reversible.
Another hallmark of chronic bronchitis is
having significant sputum production.
Emphysematous changes result from parenchymal destruction.
This leads to two different findings.
One, patients may have decreased surface area for gas exchange,
leading to problems with diffusion.
Another is that they have floppy airways that may collapse and compress,
especially in the situations of mechanical ventilation.
Here's a chest X-ray of a patient with significant COPD.
She has flattened diaphragms, enlarged lungs,
and you can see that she has compression of her cardiac silhouette.
What we worry about when these patients are placed on the mechanical ventilator
is air trapping.
As we discussed in the physiology video, air trapping
can be a potentially deadly cause of decompensation
for patients who are ventilated with obstructive lung disease.
What occurs as a patient may still be exhaling given a prolonged expiratory
phase, and the next breath will come.
This leads to trapping of air with an increase in volume and pressure
with each breath.
Over time, you can imagine that that pressure can build up and lead
to compromise in the respiratory function as well as the patient's
hemodynamics.
What we see on the patients ventilator can be the continued flow
when the next breath comes.
This is illustrated here by the red arrows on this ventilator tracing.
Note that the patient's flow has not come back up to baseline.
It has not come to 0.
This patient is still exhaling when the next breath comes.
We can't use this to quantify how much air is left in the system,
but it is an indicator that the patient is having air trapping.
The way we quantify air trapping is by checking in expiratory hold.
When we perform an expiratory hold, we stop all flow,
and the pressure that is left behind is the auto PEEP or the intrinsic PEEP.
The ventilator will tell us the total PEEP
in the system, all of the pressure.
In this example, that total PEEP is 9.8.
This patient was set on approximately 5 centimeters of water.
Therefore, the intrinsic PEEP or the auto PEEP
is 4.6 or roughly 5 centimeters of water.
So the patient's total PEEP is 10, the set PEEP is 5,
and their intrinsic PEEP or the auto PEEP was about 5.
Here's another example, two expiratory holds being performed,
one right after another.
As opposed to the last patient who had an auto PEEP of about 5,
this person has an auto PEEP or an intrinsic PEEP of about 11.
5 is an area where we would need to take action,
but 11 is very concerning because this is
pressure that's being exerted into the system that is not helpful and is not
participating in gas exchange.
One of the most important factors to address
in a patient who is being ventilated with obstructive lung disease
is their respiratory rate.
There are many ways to increase the time for a patient to exhale,
but the respiratory rate is the most efficient.
That's illustrated by the diagram here.
Here, two patients are set with the same inspiratory and expiratory
ratio of 1 to 2.
Yet one patient is being ventilated with a respiratory rate of 10,
where the other patient is being ventilated
with a respiratory rate of 20.
The red boxes indicate the exhalation time.
You can see that changing the respiratory rate from 20 down to 10 is
going to dramatically increase the amount of time that the patient has
to exhale, even for the same I:E ratio.
Therefore, when a patient has air trapping
or is having difficulty with obstructive ventilation,
decreasing the respiratory rate is one of the most important things we can do.
Here's an example of ventilator settings for a patient who
has obstructive disease.
If you look at the bottom of the ventilator screen,
you can see that the patient is set on a tidal volume of 350 mls,
has a respiratory rate of 14, a low PEEP of 5, and is set on 40% FiO2
as this patient does not have any issues with oxygenation.
I would note that the respiratory rate of 14 is adequate for this patient,
but in some circumstances it may need to be even lower.
Another thing that you may notice about this ventilator screen
is that the patient is quite dyssynchronous with the ventilator.
You can see that there are jagged, irregular tracings here.
When a patient has obstructive lung disease, just as with ARDS
or pretty much any other disease requiring mechanical ventilation,
we really don't want that patient to be dyssynchronous.
In the cases of obstructive lung disease,
when a patient is dyssynchronous with the ventilator,
this can actually worsen air trapping, as a patient
is exhaling at irregular intervals and is not exhaling fully.
If a patient has irregular breathing when they have obstructive lung
disease, it's very important to take control of that situation
and allow the patient to have plenty of time
to exhale even if that means deeply sedating the patient
or, in some circumstances, paralyzing them.
Here's another example of a patient who was intubated with reactive airways
disease.
This was a patient I took care of in the Intensive Care Unit who we did not know
had reactive airways disease.
We intubated her for another reason.
And shortly after intubation, her peak inspiratory pressure went up to 45.
This is extremely high, and I confess was somewhat unexpected.
We had the patient set on low tidal volumes of 365 and a low PEEP of 5.
And we had just intubated her, so she set at a FiO2 of 100%.
I would also note that we had the patient set
at a respiratory rate of 22.
Knowing that the patient was having an obstructive lung disease,
this is probably too high of a respiratory rate.
To evaluate her more fully, the first thing we did
was check a plateau pressure.
The plateau pressure here was only 28.
And at the moment this was checked, you can see that her peak was 39.
That's a large delta.
That's a delta of about 11 points.
That indicates that there is a significant component of resistance
rather than having a compliance problem.
So this patient was having a resistance problem, not a compliance problem.
The next thing that we did was to check an expiratory hold.
However, I will confess that we recognized
that there was a reactive airways component,
and we started to treat before we checked this ventilator screen.
The expiratory hold here shows that she has
a total PEEP of 7.3 for an intrinsic PEEP
or an auto PEEP of 2.2 centimeters of water.
So even though this patient was having a reactive airway disease component,
we were able to treat her appropriately.
In this particular situation, with giving her aggressive bronchodilators,
we were able to get her settled out and get her ventilator
settings back to normal.
PEEP is an interesting consideration in patients
who have obstructive airways disease.
In many circumstances, we want to keep the PEEP lower,
but we don't target a PEEP of 0.
Patients with obstructive airways disease
can have atelectasis and derecruitment as well.
And so we usually recommend a minimum of 5 centimeters of water
for patients who have any sort of obstructive lung disease.
However, patients who have those emphysematous changes
and the floppy airways may actually need more PEEP to stent open the airways
and paradoxically allow more air to be released.
We call this matching the PEEP.
To do this, we check the auto PEEP and determine
how much pressure is left in the system when the patient is exhaling.
We can then increase the set PEEP to the auto
PEEP to match their intrinsic PEEP.
Here's another example of a ventilator screen for a patient who
has obstructive airways disease.
We can see here that the patient is set at 450 cc.
The patient has a respiratory rate of 20--
which, again, might be a little bit too high for this patient--
a PEEP of 5, and an FiO2 of 40%.
The total PEEP in this scenario is 11, and intrinsic PEEP or an auto
PEEP measured a 5.6.
To address this, my first move would be to turn down the respiratory rate.
20 is too high for this patient and is not necessary.
Here's an example of a patient who presents with a combined resistance
problem and compliance problem.
This is a patient with very severe COPD, COPD severe
that you can't even see her diaphragms.
The lungs are so elongated and diaphragms
are flattened such that they are not visible on the screen.
You can also see that she has a very substantial left-sided pneumonia which
is causing a problem with her compliance.
She was intubated and ventilated, and this is the resulting screen.
She was set on a tidal volume of 400, which
was approximately 7 mLs per kilogram for her.
She had a respiratory rate of 16, PEEP of 10, and 100% FiO2,
as she was still profoundly hypoxemic.
Looking at her screen, you can see that she as well is not
synchronous with the ventilator at all.
She is double-triggering.
She is indicating that she has air hunger,
and she is trying to pull on the vent to get more flow.
Her peak pressure here is 54.
Seeing this, we were very concerned that she
had breath stacking, that her irregular breathing pattern was
leading to her having increased auto PEEP
and was creating a concerning scenario.
We therefore then checked her expiratory hold.
You can see here that her total PEEP was 29.
Her set PEEP was 10.
This means that she had an auto PEEP or an intrinsic PEEP of 19.
This is a tremendous amount of pressure in her intrathoracic cavity
that is leading to increased risk of hemodynamic compromise.
In this scenario, we took the patient off
of the ventilator, pressed on her chest, and allowed her to exhale.
We then put the patient back on the ventilator, sedated her very heavily,
provided neuromuscular blockade, and placed her
on a very low respiratory rate, far lower
than the 24 in which she had been set.
With these maneuvers, we were able to settle the patient out and get her
to a good place.
This concludes the video on ventilation in obstructive lung disease.
For more details, please refer to the written materials.
Thank you.