What causes chemical pneumonitis (aspiration pneumonitis) (Mendelson syndrome)?

Updated: Aug 15, 2018
  • Author: Justina Gamache, MD; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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Answer

Answer

Chemical pneumonitis, also known as aspiration pneumonitis and Mendelson syndrome, is due to the parenchymal inflammatory reaction caused by a large volume of gastric contents independent of infection. In fact, aspiration of a massive amount of gastric contents can produce acute respiratory distress within one hour. This disease occurs in people with altered levels of consciousness resulting from seizures, cerebrovascular accident (CVA), central nervous system (CNS) mass lesions, drug intoxication or overdose, and head trauma.

The acidity of gastric contents results in chemical burns to the tracheobronchial tree involved in the aspiration. If the pH of the aspirated fluid is less than 2.5 and the volume of aspirate is greater than 0.3 mL/kg of body weight (20-25 mL in adults), it has a greater potential for causing chemical pneumonitis. The initial chemical burn is followed by an inflammatory cellular reaction fueled by the release of potent cytokines, particularly tumor necrosis factor (TNF)–alpha and interleukin (IL)–8.


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