Let’s start with a CCRN® style question:
Nurse R. is taking care of a patient who is currently on rotoprone therapy related to having developed acute respiratory distress syndrome (ARDS). The physician has placed this patient on the following ventilator settings:
Tidal Volume: 420ml
Positive end expiratory pressure (PEEP): 15
The nurse knows that the purpose of the ventilation strategy above is to:
A. Promote the removal of carbon dioxide while preventing pneumothorax
B. Reduce high airway pressures and remove secretions through suctioning
C. Improve oxygenation while preventing volutrauma to the lungs
D. Mimic normal breathing patterns in order to prevent trauma to the lungs
The 3 Hidden Dangers of the Ventilator That Everyone Ignores
This exam question is tricky because when most nurses think about “trauma to the lungs” the first thing that comes to mind is Positive End Expiratory Pressure (or PEEP). Everyone knows that high levels of PEEP commonly cause pneumothorax.
Here’s my tip:
It’s important to keep in mind that there are other ways that trauma can occur related to ventilator settings. Let’s talk about the 3 most common -
Why PEEP Is More Important Than You Think
Yes, it’s true -
PEEP can cause pneumothorax. But here the thing:
When a patient is in ARDS, it’s ABSOLUTELY necessary that PEEP is placed on higher settings on the vent.
Because without PEEP you will see literally no improvement in PaO2 even with an increase in FIO2. PaO2 can only ben increased with an increase in PEEP.
You have a patient on 40% FIO2 and 5 of PEEP and SPO2 is 82%. You increase the FIO2 to 50% (with a doctor’s order of course), but SPO2 remains at 82%. You then increase the FIO2 to 60%. SPO2 remains at 82%. Then you get smart because a CCRN® told you that PEEP is the solution to ARDS problems. You then increase PEEP to 10.
Suddenly you notice something:
SPO2 is increasing!
Yay, so mission accomplished? Let’s find out why this happens:
When it comes to ARDS there’s something called “shunting” or what they call a “V/Q mismatch”. This is doctor speak referring to how the blood is traveling through the lungs, but not being oxygenated as it passes through.
PEEP opens up those avioli enough to allow for oxygenation.
PEEP is important in ARDS. Yes, it increases the chance that pneumothorax occurs, but it’s the only way to make sure that our patient gets oxygenated properly.
Don’t Make This [Doosie of a] Mistake With Tidal Volume
The most common ventilation strategy you see with ARDS patients is low tidal volume, high rate, and high PEEP settings.
In the olden days, we used to put people on MASSIVE tidal volumes. I’m talking 700-800ml - as a standard. We now know that this practice is wrong and can cause what’s known as “volutrauma”.
Volutrauma is basically a set of clinical problems that arise from giving a patient too much in tidal volume which causes alveolar rupture.
This leads to things like:
Check it out:
The combination of high rate and low volume to prevent volutrauma is ideal in the presence of an increased PEEP which allows for the avioli to stay opened. The high rate plus low volume combination provide a proper volume per minute and keeps the patient safe.
The dangers of being careless with FIO2
In case you didn’t know this already:
When FIO2 (aka fraction of inspired oxygen) is > 60%, damage to the lung occurs.
The fine folks over at uptodate put it this way -
Although supplemental oxygen is valuable in many clinical situations, excessive or inappropriate supplemental oxygen can be deleterious. According to human and animal studies, high concentrations of inspired oxygen can cause a spectrum of lung injury, ranging from mild tracheobronchitis to diffuse alveolar damage (DAD)
High levels of FIO2 can cause some bad stuff to happen when it comes to gas exchange in the lungs and even the lung tissues themselves.
“Bad stuff” is a fancy term referring to oxygen toxicity:
Oxygen toxicity that term is usually reserved for reference to alveolar trauma and tracheobronchial damage, but may also include -
Diminished lung volumes
Hypoxemia related to the atelectasis
And even parenchyma
If you read the rationale above, this CCRN® Question should be in the bag.
What’s the correct answer?
Leave a comment with your thoughts below:
Thanks for reading.