Nitrogen Dioxide

Etiology

  • Silo Filler’s Disease
    • Farmer inhalational exposure to decomposing organic matter in silo (usually occurs within 2 weeks after filling silo)
    • Nitrogen dioxide gas is released from decomposition of organic matter
  • Internal Combustion Engine: inhalational exposure in enclosed space (example: ice resurfacing in indoor skating rinks)
  • Explosion or Fire: thermal degradation of polymers -> inhalational exposure
  • Industrial Exposure: release of compressed nitrogen dioxide gas
  • Gas-Shielded Welding: manual inert gas or tungsten inert welding -> inhalational exposure
  • Detonation of Explosives: inhalational exposure
  • Inhaled Nitric Oxide (NO) Therapy (see Nitric Oxide, [[Nitric Oxide]]): in presence of oxygen, NO breaks down into nitrogen dioxide
    • Requires monitoring of NO2 levels during NO therapy
  • Nitric Acid Treatment of Wood: releases nitrogen dioxide

Physiology

  • Nitrogen Dioxide Gas Inhalation: nitrogen dioxide gas has a distinctive red-brown color and is heavy
    • Highest concentrations occur just above the silage (in the case of silo-related exposures)
    • Low Water Solubility: may result in longer exposure and delayed injury to bronchioles and alveoli before the vicitim becomes aware of the exposure
  • Nitrogen Dioxide Gas Increases Airway Epithelial Permeability: may allow direct stimulation of airway smooth muscle or stimulate parasympathetics (with resulting bronchoconstriction)

Diagnosis

  • FOB: necessary to rule out airway injury
  • CXR/Chest CT Patterns (depends on degree of exposure)
    • Normal CXR: some cases
      • Normal CXR does not rule out significant injury or possibility of later developing symptoms
    • Diffuse Nodular Infiltrates: some cases
    • Pulmonary Edema: some cases with severe exposure

Clinical Presentations

(delayed onset of pulmonary injury -> symptoms may occur hours-days later in some cases)

  • Silo Filler’s Disease
    • Clinical
      • Minimal upper airway injury and conjunctival irritation
      • Dyspnea
      • Choking sensation
      • Cough with frothy or mucoid sputum
    • Diagnosis
      • CXR/Chest CT
        • Normal CXR: normal CXR does not rule out significant injury or possibility of later developing symptoms
        • Diffuse Micronodular/Nodular Infiltrates (see Lung Nodule or Mass, [[Lung Nodule or Mass]]): may be seen in subacute exposure
        • Diffuse Infiltrates (see Pneumonia, [[Pneumonia]]): may be seen with acute exposure
  • Acute Lung Injury-ARDS (see Acute Lung Injury-ARDS, [[Acute Lung Injury-ARDS]])
    • Epidemiology: with high-level exposure
    • Pathology: diffuse alveolar damage
    • Clinical: may be rapid in onset
  • Bronchiolitis Obliterans (see Bronchiolitis Obliterans, [[Bronchiolitis Obliterans]])
    • Epidemiology: occurs in only 1 in 20 cases with moderate-severe exposure
  • Cryptogenic Organizing Pneumonia (see Cryptogenic Organizing Pneumonia, [[Cryptogenic Organizing Pneumonia]])
  • Reactive Airway Dysfunction Syndrome (see Reactive Airway Dysfunction Syndrome, [[Reactive Airway Dysfunction Syndrome]])
    • Epidemiology: may be seen in some cases
  • Pulmonary Alveolar Proteinosis (see Pulmonary Alveolar Proteinosis, [[Pulmonary Alveolar Proteinosis]])

Treatment

  • Avoid Exposure: do not enter silo until >2 weeks after filling
  • Steroids: may be benficial in acute lung injury, but unproven

References

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