Negative Pressure Pulmonary Edema and Croup

Negative Pressure Pulmonary Edema and CroupCaring for patients is very humbling. I once described the EM Mindset as being one that requires Humble Arrogance (See – requiring humility to know you can’t know it all and arrogance to believe that your skills can make a difference in another’s life.  Certainly, this requires a continual assessment of the balance between the two extremes.  Sometimes that balance is easy, but other times we don’t even recognize the disequilibrium until our patients alert us to it. Recently, a patient reminded me that, while most croup is rather benign, it can become complicated. Let us use my recent humbling experience to refresh our memories about Negative Pressure Pulmonary Edema and Croup.


Croup: What is Usual

  • Usually caused by a virus
  • Usually 1-2 episodes per year
  • Usually seen in the Fall and Winter months
  • Usually affects children 6 mos – 3 years with peak at 2 years
  • Usually short in duration (1-2 days)
  • Usually standard therapies effectively treat the condition.
  • Usually does NOT require hospitalization.


Croup: What is Feared

  • Airway Obstruction
    • Obviously, this is the major emergent condition that needs to be avoided.
    • This is why stridor garners so much attention in the ED.
  • Negative Pressure Pulmonary Edema
    • Occurs as a result of the airway obstruction and leads to pulmonary edema and hypoxia. [Chen, 2010]
    • May be present even after obstruction has resolved.


Negative Pressure Pulmonary Edema

  • Also referred to as “Post-Obstructive Pulmonary Edema”
  • Can be caused from severe, sudden upper airway obstruction (Type I)
    • Cases reported due to laryngospasm, epiglottis, croup, aspirated FB’s, and angioedema. [Chen, 2010]
    • Even seen in agitated patient after biting down on endotracheal tube. [Bhattacharya, 2016]
    • Can also develop after surgery (especially ENT T&A surgery) for upper airway obstruction. (Type II) [Sonsuwan, 2014; Mehta, 2006]
  • Forced inspiration against a closed or obstructed glottis generates excessive negative intrathoracic pressures [Bhattacharya, 2016]
    • Known as Muller Maneuver.
    • -140 cm H2O compared to baseline of -4 cm H2O
  • This increases venous return to right heart and increases pulmonary venous pressures.
  • Additionally, low cardiac output leads to increased high afterload pressures.
  • These combine to cause increased hydrostatic pressures –> fluid moves from pulmonary vasculature to the interstitial space –> Pulmonary Edema –> Hypoxia
  • Acute airway obstruction can also lead to hypoxia, which further causes pulmonary vasoconstriction, pulmonary hypertension, and right heart failure.
  • Usually occurs within minutes of airway obstruction; often resolves within 12-24 hours. [Bhattacharya, 2016Chen, 2010]



  • May present with obvious signs of upper airway obstruction (stridor, increased work of breathing/retractions, hoarseness, drooling).
    • May also present after the episode of obstruction resolved (so, perhaps you took appropriate actions to fix the problem with positioning, medications, or intubation).
  • Signs of Pulmonary Edema [Chen, 2010]
    • Hypoxemia
    • Frothy sputum in nonintubated patient or edema fluid in endotracheal tube.
    • Bilateral infiltrates on CXR



  • Early recognition is important (remember, hypoxia in a patient with “croup” is odd).
  • Beta-agonists may help improve fluid clearance. [Bhattacharya, 2016]
  • Supplemental oxygenation
  • May need Positive Pressure Ventilation
  • Use of diuretics
    • Still controversial [Chen, 2010]
    • May be beneficial, if patient is not hypotensive. [Bhattacharya, 2016]
  • May require Prone Positioning or even ECMO.


Moral of the Morsel

  • Even the Simple can become Complicated! Remain Vigilant!
  • Even the Common can cause Humility.
  • Not all that has stridor has croup: don’t bark up the wrong tree.
  • Not all croup is simple: if there is hypoxia, think about negative pressure pulmonary edema.



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Sean M. Fox
Sean M. Fox

I enjoy taking care of patients and I finding it endlessly rewarding to help train others to do the same. I trained at the Combined Emergency Medicine and Pediatrics residency program at University of Maryland, where I had the tremendous fortune of learning from world renowned educators and clinicians. Now I have the unbelievable honor of working with an unbelievably gifted group of practitioners at Carolinas Medical Center. I strive every day to inspire my residents as much as they inspire me.

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