Asynchrony PEM: Pediatric Airway Obstruction
Pediatric Airway Obstruction
Team A to the trauma room! You start assessing your patient’s C-A-Bs, and you’re stuck on Airway… this kid is struggling to BREATHE!
Foreign bodies are terrifying, but there are many causes of pediatric upper airway obstruction, such as croup, epiglottitis, angioedema, abscesses -- it's a big, scary picture.
So let’s take a moment to back up a little bit. What does upper airway obstruction sound like? Well, let’s first start with some physics (feel free to completely skip over this part, but as an engineer I couldn’t help myself). We’re going to take a walk down memory lane and bring back some old friends, namely the Bernoulli Principle and Poisseuille’s Law. Remember this equation?
The important variables here are Q (flow), P (pressure), and r (radius). As radius decreases, flow decreases. Applied to our patient population, a 1mm reduction in the 4mm diameter of a neonatal airway results in a 75% decrease in airflow. When the velocity increases to compensate, this exerts negative pressure on the walls of the lumen, precipitating airway collapse. This is what happens when you fly a plane, as illustrated in this video! (only listen to 1:05 through 1:38) and in the figure below:
Well, that was fun!
Now let’s talk about how the sound you’re hearing can tell you about the nature of obstruction. There are a couple of different types of stridor: inspiratory, expiratory, and biphasic. What does the sound we hear tell us about the location of the blockage? Take a look at the figure below, and let’s go back to those principles we just spoke about.
Ida JB, Thompson DM. Pediatric stridor. Otolaryngol Clin North Am. 2014 Oct;47(5):795-819. doi: 10.1016/j.otc.2014.06.005
Above the glottis, the hypermobile soft tissues of the airway will collapse with the negative pressure of an inspiratory force, causing inspiratory stridor. The glottis is more limited in its ability to expand or collapse with increased air velocity, thus stridor is likely to be audible in both phases of the respiratory cycle. Below the level of the vocal cords, sounds will depend upon whether they are intra- or extra-thoracic. If intra-thoracic, dynamic collapse will occur on expiration, when there is positive intra-thoracic pressure on the airway. The opposite is true above the thorax. Alright, if you made it to this point, hopefully you have a solid understanding of all those crazy respiratory sounds you might hear in the Peds ED!
Now that we know what we’re listening for, what’s on our differential for our patient who’s struggling to breathe? What could be obstructing our patient’s airway? Here is an overview of some things to keep on your differential, and which kids are susceptible to which causes of obstruction (and includes a section on foreign body aspiration.) If you prefer the lecture format, this podcast may be a great intro to the topic for you. I guess in the UK they use nebulized adrenaline, which here we call racemic epinephrine. Here’s another nice overview of upper airway obstruction differential and management from Don’t Forget the Bubbles .
What is the most common cause of upper airway obstruction in children? I’ll give you a hint - it sounds like this:this .
You guessed it, croup! Remember that steeple sign? Read this from PEMBlog. Read some more on croup here on Don’t Forget the Bubbles. Also ALiEM has a nice pocket card on croup for your smartphone. Remember, it’s important to keep these kids calm, because agitation causes tachypnea -- which increases negative intrathoracic pressure, which further draws air past that already narrow airway, generating “lift” and increasing the obstruction (see the physics explanation above). As common as croup is, beware of recurrent croup, which should be a red flag to start thinking of other causes, including anatomic abnormalities.
Let’s talk a little about some other important items on the differential: Epiglottitis, peritonsillar abscess, pharyngitis, and angioedema: EM Cases has a great podcast on this. Start at 1:23. Here’s another great review of differentiating causes of stridor and drooling. Pediatric EM Morsels has a short review of bacterial tracheitis. Lastly, be wary of this feared complication of upper airway obstruction: negative pressure pulmonary edema.
What about stridor that has been going on for a while? What kinds of things should be on our differential for the little ones? Take a look at this case from Las Vegas EM.
Here’s another diagnosis to keep in mind - Vocal Cord Dysfunction. This can present to the ED as wheezing, stridor, or upper airway obstruction, and often goes misdiagnosed for a prolonged period of time. It is not uncommon for these patients to receive unnecessary treatments including bronchodilators, intubation, and tracheostomy due to failure to properly diagnose the condition.
Let’s put ourselves to the test with this great case from PEM Academy.
Finally, what do you do if this kid with a critical upper airway obstruction fails non-invasive measures? Here’s a good overview of intubating a kid with stridor from Don’t Forget the Bubbles .
That's it -- now you're ready to be the hero in your next pediatric upper airway emergency.
See you next time in Asynchrony EM!