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Lung aspiration syndromes

Risk factors

Decreased consciousness
Impaired cough and gag reflex

  • recent extubation
  • neurological disease
  • neck or pharyngeal trauma or surgery
  • elderly patients

Passive regurgitation

  • pregnancy
  • emergency surgery with full stomach
  • NG tubes
  • reflux
  • oesophagectomy
  • oesophageal obstruction
  • achalasia, scleroderma
  • raised intra-abdominal pressure


Aspiration of solids

  • aspiration of large particles causes upper airway obstruction
  • smaller particles aspirated into lung where they may cause atelectasis distal to the obstruction
  • some irritative particles (eg meat, vegetable products) may cause a localized pneumonitis which may progress to necrotizing pneumonia, abscess formation, and empyema. Bronchiectasis may follow.
  • presentation of small particle partially obstructive aspiration is with dyspnoea, persistent coughing, wheeze, stridor and hypoxaemia
  • non-obstructive particulate aspiration causes a clinical and radiological picture similar to that of acid aspiration

Acid aspiration

  • causes extensive lung damage that starts within minutes of aspiration. Alveolar epithelial and endothelial damage with atelectasis from surfactant dysfunction. Fluid and protein leak into alveoli and bronchi immediately, becoming severe within an hour: permeability pulmonary oedema. Polymorphonuclear infiltration leads to alveolar consolidation. Most severe injury occurs with an aspirate pH<2.5
  • gastric contents in previously healthy patients are acidic and free from bacterial colonization and therefore infection is not important in the early stages of acid aspiration lung injury
  • causes vagally mediated bronchospasm

Non-acid liquid aspiration

  • blood, isotonic solutions, salt or fresh water produce limited pulmonary injury. Usually resolves over days
  • large volume aspiration (eg near drowning) may be associated with severe lung dysfunction

Aspiration of infected fluids

  • initial damage similar to acid aspiration but respiratory tract infection and pneumonia supervene
  • in non-hospitalized patients anaerobic oral flora sensitive to penicillin dominate
  • in critically ill enteric gram negatives dominate
  • microscopic aspiration thought to be a major factor in the development of nosocomial pneumonia

Aspiration of hydrocarbons

  • 20% of aspiration accidents in children < 5 yrs
  • pulmonary damage results from dissolution of membrane lipids and surfactant inactivation
  • large aspirates associated wit pulmonary oedema and haemoptysis


  • ? evidence of risk factors
  • ETT suctioning to detect gastric contents or acidic pH on specific testing. Aspirates should all be gram stained and cultured
  • fibreoptic bronchoscopy to identify particulate matter
  • clinical examination to detect laryngeal incompetence
  • Ba swallow in difficult cases


  • correct hypoxaemia
  • inhaled/nebulized bronchodilators for aspiration induced bronchospasm despite relatively poor efficacy. Aminophylline adds little and has significant risks
  • outpouring of protein rich fluid into lung in severe acid aspiration may lead to relative intravascular hypovolaemia. Whether the optimal fluid management is fluid administration or restriction is unclear. Inotropes may be required
  • therapeutic bronchoscopy if there is particulate aspiration, focal pulmonary collapse or CXR evidence of foreign body. Rigid procedure of choice to remove semisolid material and most inhaled objects. Flexible for small solid particles
  • antibiotics for secondary bacterial infection and infected fluid aspiration. Antibiotics depend on setting (ie community/hospital) and whether aspiration was of liquid or solid. For pneumonia secondary to aspiration of solid particles cover anaerobes with penicillin or clindamycin
  • steroids are not of proven benefit and may slow pulmonary healing

Further reading

Cooper DJ. Aspiration syndromes. In Oh TE (ed), Intensive Care Manual, 4th Ed., Butterworth Heinemann, Oxford, 1997, pp 319-26


© Charles Gomersall December 1999

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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