Negative pressure pulmonary edema

Background

• Also known as post-obstructive pulmonary edema
• Forced inspiration against obstructed airway causes large negative intrathoracic pressure, leading to pulmonary edema
• Mostly due to postoperative laryngospasm, sudden drops in PEEP (high PEEP to manual BVM), trauma such as hanging, strangulation, foreign bodies, etc.
• The negative pressure causes hydrostatic edema that can be life-threatening if not but minimized if treated early, usually resolves after 24-48 hours.
• Patients have an airway obstructive process either from an allergy, laryngospasm, trauma, and commonly in the case of hangings.

Clinical Features

• Hypoxemia (may be sudden and large - beware "fake" or "not real" SpO2), stridor, retractions, accessory muscle use, crackles/wheezes
• Crackles
• Respiratory distress
• Increased jugular venous distension
• Signs of poor organ perfusion

Differential Diagnosis

Pulmonary Edema Types

Pulmonary capillary wedge pressure <18 mmHg differentiates noncardiogenic from cardiogenic pulmonary edema

• Cardiogenic pulmonary edema
• Noncardiogenic pulmonary edema
  • Negative pressure pulmonary edema
    • Upper airway obstruction
    • Reexpansion pulmonary edema
    • Strangulation
  • Neurogenic causes
    • Seizure
    • Head trauma
    • Subarachnoid hemorrhage
    • Electrocution
  • Iatrogenic fluid overload
    • Multiple blood transfusions
    • IV fluid
    • Inhalation injury
    • Pulmonary contusion
    • Aspiration pneumonia and pneumonitis
  • Other
    • High altitude pulmonary edema
    • Hypertensive emergency
    • ARDS
    • Flash pulmonary edema
    • Immersion pulmonary edema
    • Hantavirus pulmonary syndrome
    • Missed dialysis in kidney failure
    • Naloxone reversal

Evaluation

• CXR shows diffuse interstitial and alveolar infiltrates
• CT shows preferential central/nondependent distribution of edema (as opposed to other forms of pulmonary edema)

Management

• Relieve airway obstruction/obstructive processes
• Vent with generous PEEP and diuretics
• Intubation is often required
• Patients with severe pulmonary edema that do not respond to standard ventilator strategies may require proning or even ECMO

Disposition

• Admit, often ICU

See Also

• Pulmonary edema