UMEM Educational Pearls

Negative-pressure pulmonary edema (NPPE) is a well-documented entity that occurs after a patient makes strong inspiratory effort against a blocked airway. The negative pressure causes hydrostatic edema that can be life-threatening if not recognized, but if treated quickly and appropriately, usually resolves after 24-48 hours. These patients may have any type of airway obstruction, whether due to edema secondary to infection or allergy, laryngospasm, or traumatic disruption of the airway, such as in attempted hangings.

Management: 

1.     Alleviate or bypass the airway obstruction.

·      Usually via intubation; may require a surgical airway

·      If obstruction in an intubated patient is due to biting on tube or dyssynchrony, add bite-block (if not already in place), sedation, and even paralysis if needed.

2.     Provide positive pressure ventilation and oxygen supplementation.

3.     Use low tidal volume ventilation.

4.     In severe hypoxemia without shock, add a diuretic agent and consider additional measures such as proning and even ECMO if the hypoxemia is refractory to standard therapy.  

Additional Information

Negative-pressure pulmonary edema (NPPE), also called post-obstructive pulmonary edema, can occur after any event in which a patient exerts strong inspiratory effort against an obstructed airway. This obstruction can be essentially due to any cause; in adults it is most well-documented secondary to post-extubation laryngospasm, in children the etiology is usually infectious, such as in epiglottitis. It has also been documented secondary to laryngeal edema, tumor, trauma, biting on an endotracheal tube, vent dyssynchrony,  as well as disruptions to breathing mechanics during generalized seizures, among other causes.

It is noted that many of the documented cases involve patients who are relatively young and otherwise healthy, and thus capable of creating a strong negative intrathoracic pressure. The pathophysiology is thought to be related to hydrostatic mechanisms rather than a “leaky-capillary” permeability edema, and it usually resolves quickly if managed appropriately, within 24-48 hours. Diffuse alveolar hemorrhage, related to capillary rupture from the negative pressure, has been documented to occur in severe cases but is rare.

Consider the diagnosis in patients with an appropriate clinical picture or witnessed event leading to abrupt respiratory distress and/or failure. The diagnosis is even more strongly supported if they had absence of respiratory symptoms, or a clear chest x-ray prior to the event, with a chest x-ray demonstrating pulmonary edema afterwards.

Appropriate management of these patients includes:  

1.     Alleviation or bypass of the upper airway obstruction, which usually requires intubation.

·      Depending on the etiology of obstruction (e.g. epiglottitis), endo/nasotracheal intubation may be difficult and a surgical airway may be necessary. Be prepared for this possibility.

·      Ventilated patients who develop NPPE may require sedation to prevent biting on the ETT or to promote vent synchrony

2.     Provide with positive-pressure ventilation to counteract the negative airway pressures, and oxygen supplementation to decrease pulmonary vascular resistance.

3.     Lung-protective ventilation with low tidal volumes is generally accepted as the preferred ventilation strategy in these patients, extrapolated from data regarding its use in acute lung injury.

4.     In cases of moderate to severe hypoxemia without the presence of shock, add a diuretic agent.

5.     For refractory hypoxemia, consider early utilization of additional therapies, including neuromuscular blockade, proning, and ECMO. 

References

Bhattacharya M, Kallet RJ, Ware LB, Matthay MA. Negative-pressure pulmonary edema. Chest. 2016;150(4):927-33. 

Contou D, Voiriot G, Djibre et al. Clinical features of patients with diffuse alveolar hemorrhage due to negative-pressure pulmonary edema. Lung. 2017;195(4):477-487.