Aspiration pneumonia pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sunny Kumar MD [2], Sadaf Sharfaei M.D.[3]

Overview

Aspiration pneumonia is a common pneumonia among patients with risk factors including neurologic diseases. Microaspiration and macroaspiration of different materials are the primary cause of aspiration pneumonia. The mechanism behind damage of lung due to aspiration depends on the content of aspirate and the response of lung tissue to the content. Host factors including mucociliary clearance, cough reflex, and immune system might be impaired. Chemical pneumonitis usually occurs following aspiration of materials that are toxic to pulmonary tissue. There might be no bacterial or viral organisms involved. It is mostly associated with aspiration of gastric acid. In case of oropharyngeal secretions the damage is due to bacteria infecting and inducing inflammation in lung tissues. Foreign body aspiration might present acutely with mechanical obstruction or chemical pneumonitis. Lipoid pneumonia is caused by aspiration of mineral oil when used for constipation treatment. Following oil aspiration there is an inflammatory response with regional edema, acute cough, fever, and dyspnea. Patients with genetic syndromes and paralysis of lower cranial nerves might be prone to aspiration pneumonia. On gross pathology, different aspirated particles might be seen. On microscopic histopathological analysis, aspirated material fragments, inflammation, fibrosis, and skeletal muscle fibers might be seen.

Pathophysiology

To understand the pathogenesis we have to review following physiological facts regarding aspiration pneumonia:[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]

Mode of Transmission

Inhalation of Aerosolized Droplets

Inhalation of aerosolized droplets of 0.5 to 1 micrometer is the most common pathway of acquiring pneumonia. A few bacterial and viral infections are transmitted in this fashion. The lung can normally filter out particles between 0.5 to 2 micrometer by recruiting the alveolar macrophages.

Microaspiration of Oropharyngeal Contents

Aspiration of oropharyngeal contents containing pathogenic microorganisms is one of the mechanisms of acquiring pneumonia. It most commonly occurs in normal persons during sleep, in unconscious persons due to gastroesophageal reflux or impaired gag reflex and cough reflex.

Agent Specific Virulence Factors

Several strategies are evolved to evade host defense mechanisms and facilitate spreading before establishing an infection.

Host Factors

1. Diminished Mucociliary Clearance
2. Impaired Cough Reflex
3. Defective Immune System

Chemical Pneumonitis

Bacterial Infection

Foreign body aspiration

Lipoid Pneumonia

Genetics

Gross Pathology

Aspirated corn kernel By Yale Rosen from USA - Uploaded by CFCF, CC BY-SA 2.0, Via Wikimedia[18]
Aspirated vomitus occluding the main stem bronchi. By Yale Rosen from USA - AspirationUploaded by CFCF, CC BY-SA 2.0, Via Wikimedia[19]


Microscopic Pathology

Aspirated vegetable material surrounded by macrophages. This structure has a thick outer wall composed of cellulose surrounding a latticework of individual cells with thick cell walls composed of cellulose. By Yale Rosen from USA - Aspiration pneumoniaUploaded by CFCF, CC BY-SA 2.0, Via Wikimedia[20]
Acute aspiration pneumonia with numemous Skeletal muscle fibers and a vegetable fragment infiltrated by polys. By Yale Rosen from USA - Aspiration pneumoniaUploaded by CFCF, CC BY-SA 2.0, Via Wikimedia[21]
Intraalveolar kayexalate crystal; acute Pneumonitis. By Yale Rosen from USA - Kayexalate aspiration Case 125Uploaded by CFCF, CC BY-SA 2.0, Via Wikimedia[22]
Numerous interstitial fat globules of varying size accompanied by Inflammation and fibrosis is characteristic of chronic lipid pneumonia secondary to lipid aspiration. By Yale Rosen from USA - Lipid pneumonia, exogenousUploaded by CFCF, CC BY-SA 2.0, Via wikimedia[23]


References

  1. Hu X, Lee JS, Pianosi PT, Ryu JH (2015). "Aspiration-related pulmonary syndromes". Chest. 147 (3): 815–823. doi:10.1378/chest.14-1049. PMID 25732447.
  2. Japanese Respiratory Society (2009). "Aspiration pneumonia". Respirology. 14 Suppl 2: S59–64. doi:10.1111/j.1440-1843.2009.01578.x. PMID 19857224.
  3. Almirall J, Cabré M, Clavé P (2012). "Complications of oropharyngeal dysphagia: aspiration pneumonia". Nestle Nutr Inst Workshop Ser. 72: 67–76. doi:10.1159/000339989. PMID 23052002.
  4. Marik PE, Careau P (1999). "The role of anaerobes in patients with ventilator-associated pneumonia and aspiration pneumonia: a prospective study". Chest. 115 (1): 178–83. PMID 9925081.
  5. Cordier JF, Cottin V (2013). "Neglected evidence in idiopathic pulmonary fibrosis: from history to earlier diagnosis". Eur Respir J. 42 (4): 916–23. doi:10.1183/09031936.00027913. PMID 23598958.
  6. Shi X, Zheng J, Yan T (2018). "Computational redesign of human respiratory syncytial virus epitope as therapeutic peptide vaccines against pediatric pneumonia". J Mol Model. 24 (4): 79. doi:10.1007/s00894-018-3613-z. PMID 29500665.
  7. Shen CF, Wang SM, Ho TS, Liu CC (2017). "Clinical features of community acquired adenovirus pneumonia during the 2011 community outbreak in Southern Taiwan: role of host immune response". BMC Infect Dis. 17 (1): 196. doi:10.1186/s12879-017-2272-5. PMC 5341368. PMID 28270104.
  8. Marik PE (2011). "Pulmonary aspiration syndromes". Curr Opin Pulm Med. 17 (3): 148–54. doi:10.1097/MCP.0b013e32834397d6. PMID 21311332.
  9. Hu X, Lee JS, Pianosi PT, Ryu JH (2015). "Aspiration-related pulmonary syndromes". Chest. 147 (3): 815–823. doi:10.1378/chest.14-1049. PMID 25732447.
  10. DiBardino, David M.; Wunderink, Richard G. (2015). "Aspiration pneumonia: A review of modern trends". Journal of Critical Care. 30 (1): 40–48. doi:10.1016/j.jcrc.2014.07.011. ISSN 0883-9441.
  11. Taylor, Joanne K.; Fleming, Gillian B.; Singanayagam, Aran; Hill, Adam T.; Chalmers, James D. (2013). "Risk Factors for Aspiration in Community-acquired Pneumonia: Analysis of a Hospitalized UK Cohort". The American Journal of Medicine. 126 (11): 995–1001. doi:10.1016/j.amjmed.2013.07.012. ISSN 0002-9343.
  12. Hu, Xiaowen; Lee, Joyce S.; Pianosi, Paolo T.; Ryu, Jay H. (2015). "Aspiration-Related Pulmonary Syndromes". Chest. 147 (3): 815–823. doi:10.1378/chest.14-1049. ISSN 0012-3692.
  13. Lanspa, Michael J.; Jones, Barbara E.; Brown, Samuel M.; Dean, Nathan C. (2013). "Mortality, morbidity, and disease severity of patients with aspiration pneumonia". Journal of Hospital Medicine. 8 (2): 83–90. doi:10.1002/jhm.1996. ISSN 1553-5592.
  14. Lanspa, Michael J.; Jones, Barbara E.; Brown, Samuel M.; Dean, Nathan C. (2013). "Mortality, morbidity, and disease severity of patients with aspiration pneumonia". Journal of Hospital Medicine. 8 (2): 83–90. doi:10.1002/jhm.1996. ISSN 1553-5592.
  15. Marik, Paul E. (2001). "Aspiration Pneumonitis and Aspiration Pneumonia". New England Journal of Medicine. 344 (9): 665–671. doi:10.1056/NEJM200103013440908. ISSN 0028-4793.
  16. 16.0 16.1 Japanese Respiratory Society (2009). "Aspiration pneumonia". Respirology. 14 Suppl 2: S59–64. doi:10.1111/j.1440-1843.2009.01578.x. PMID 19857224.
  17. 17.0 17.1 Almirall J, Cabré M, Clavé P (2012). "Complications of oropharyngeal dysphagia: aspiration pneumonia". Nestle Nutr Inst Workshop Ser. 72: 67–76. doi:10.1159/000339989. PMID 23052002.
  18. "File:Aspirated corn kernel (3791886968).jpg - Wikimedia Commons".
  19. "File:Aspiration (4858360012).jpg - Wikimedia Commons".
  20. "File:Aspiration pneumonia (5613726286).jpg - Wikimedia Commons".
  21. "File:Aspiration pneumonia (5613146123).jpg - Wikimedia Commons".
  22. "File:Kayexalate aspiration Case 125 (4692318776).jpg - Wikimedia Commons".
  23. "File:Lipid pneumonia, exogenous (3791887936).jpg - Wikimedia Commons".