Condition

Aspiration Pneumonia

Editors: Graeme P. Currie MBChB, DCH, PG Dip (Med Ed), MSc, FRCP (Edin), MD ; Terence K. Trow MD, FACP, FCCP; Amir Qaseem MD, PhD, MHA, MRCP (London), FACP; Paritosh Prasad MD

American College of PhysiciansProduced in collaboration with American College of Physicians
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Background Information

Description

  • Aspiration pneumonia refers to an infection of the lung parenchyma following the inhalation of a large amount (macroaspiration) of colonized oropharyngeal or gastric material.,,

Definitions

  • Aspiration pneumonia is an infection due to the inhalation of oropharyngeal or upper gastrointestinal contents colonized by pathogenic bacteria. This term is reserved for an acute lung infection developing after a large amount of material is aspirated (vs. microaspiration which is the initial step in pathogenesis of most bacterial pneumonia).,,
  • Aspiration pneumonitis (Mendelson syndrome, also called chemical pneumonitis) is an inflammatory reaction caused by the inhalation of acidic gastric contents.,,

Epidemiology

Incidence/Prevalence

  • The true incidence of aspiration pneumonia is difficult to estimate as most aspiration events go unwitnessed or are silent.
    • It is estimated that about 90% of intensive care unit (ICU) patients have ≥ 1 aspiration event.
    • An estimated 3 aspiration events are reported per every 10,000 anesthetic procedures.
    • The incidence is likely higher in special populations and during emergency situations.
    • Reference - J Dent Anesth Pain Med 2017 Mar;17(1):1
  • Aspiration pneumonia is reported to account for 5%-15% of all cases of community-acquired pneumonia.
  • STUDY SUMMARY
    aspiration may be cause of pneumonia in 10% of adults hospitalized for community-acquired pneumonia and 30% of adults hospitalized for pneumonia from continuing care facilities
    CROSS-SECTIONAL STUDY: J Am Geriatr Soc 2006 Feb;54(2):296

  • STUDY SUMMARY
    estimated incidence of aspiration pneumonia 15 times greater in adults ≥ 65 years old compared to adults < 65 years old
    POPULATION-BASED SURVEILLANCE: Ann Am Thorac Soc 2017 Jun;14(6):874

Risk Factors

  • Risk factors include a history of a medical condition that predisposes patients to aspiration, such as:,,
    • Impaired swallowing (esophageal dysphagia or oropharyngeal dysphagia) due to:
    • Altered mental status due to:
      • Alcohol intoxication
      • Drug overdose
      • Stroke, seizure, cardiac arrest, or head trauma
      • Anesthesia or conscious sedation
      • Medication use, including narcotic agents, sedatives, and antidepressant medications
    • An impaired cough reflex
    • Conditions associated with increased risk of gastric contents reaching the lungs, such as:
  • Other risk factors include:
    • Hospitalization or chronic institutionalization
    • Prolonged supine position (J Dent Anesth Pain Med 2017 Mar;17(1):1)
  • Other potential risk factors include:,
    • Male sex
    • Smoking
    • Diabetes mellitus
    • Recurrent vomiting
    • Oropharyngeal colonization
  • Use of medications such as H2-receptor antagonists or proton-pump inhibitors do not increase risk of aspiration but may alter gastric pH allowing the growth of potentially pathogenic organisms within gastric aspirations.
  • STUDY SUMMARY
    poor oral condition, cognitive impairment, and cerebrovascular disease associated with aspiration pneumonia in older adults
    COHORT STUDY: Clin Oral Investig 2018 Sep;22(7):2575

  • STUDY SUMMARY
    dehydration, recent deterioration of swallowing function, sputum suctioning, and dementia associated with aspiration pneumonia in adults ≥ 65 years old in long-term care
    COHORT STUDY: PLoS One 2015;10(10):e0140060

  • STUDY SUMMARY
    neurologic deficit after surgery and history of cerebral vascular disorder associated with increased risk of aspiration pneumonia in elderly patients having cardiovascular surgery
    COHORT STUDY: Gen Thorac Cardiovasc Surg 2017 Feb;65(2):96

  • STUDY SUMMARY
    among adults with type 2 diabetes having upper gastrointestinal endoscopy, use of glucagon-like peptide-1 receptor agonist within 30 days before upper endoscopy may not increase risk of pulmonary aspiration on day of or during procedure but may increase risk of discontinuation of procedure compared to use of sodium-glucose cotransporter-2 inhibitor
    COHORT STUDY: BMJ 2024 Oct 22;387:e080340

Etiology and Pathogenesis

Pathogens

  • The etiology of aspiration pneumonia has shifted away from predominantly anaerobes to pathogens commonly associated with community- and hospital-acquired pneumonia.
  • Common pathogens isolated from patients with community-acquired aspiration pneumonia include:
    • Streptococcus pneumoniae
    • Staphylococcus aureus
    • Haemophilus influenzae
    • Enterobacteriaceae
  • Pathogens isolated in patients with hospital-acquired aspiration pneumonia may include gram-negative organisms, such as Pseudomonas aeruginosa. ,
  • Anaerobic pathogens are more likely in patients with risk factors such as severe periodontal disease, necrotizing pneumonia, or lung abscess.
  • STUDY SUMMARY
    multi-drug resistant or extensively-drug resistant pathogens more common etiology in patients with healthcare-associated aspiration pneumonia
    COHORT STUDY: Infez Med 2018 Jun 1;26(2):103

Pathogenesis

  • Aspiration of colonized oropharyngeal or upper gastric material is the primary mechanism by which bacteria gain entrance to the lungs.
    • Aspiration occurs in about half of healthy adults during sleep. Typically infection does not occur, presumably due to:
      • Small inoculum (microaspiration) of bacteria
      • Normal cough reflex
      • Active mucociliary clearance
      • Intact immune system
    • Infection is thought to occur if mechanical or immune function is impaired, or if a high inoculum of bacteria is present.
    • PubMed31516051Expert review of clinical pharmacologyExpert Rev Clin Pharmacol201910011210991-1002991References - , Expert Rev Clin Pharmacol 2019 Oct;12(10):991
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Produced in collaboration with American College of Physicians
American College of Physicians

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