aspiration pneumonia

Etiology

• impaired swallowing - xerostomia
• large-volume aspiration occurs with dysphagia
  • head & neck cancer
  • esophageal cancer
  • esophageal stricture
  • esophageal motility disorders
• chronic obstructive pulmonary disease
• depressed gag reflex, ineffective cough reflex
• cardiac arrest
• tracheal or nasogastric tube
• transient impaired consciousness in the wake of seizures
• cerebrovascular accidents (stroke)
• alcoholic blackouts or impaired consciousness from drug abuse
• in institutionalized elderly, bacteria responsible for aspiration pneumonia appear to arise from plaque associated with natural teeth & with dental prosthesis
• pathogenic bacteria responsible for aspiration pneumonia may also originate from pharyngeal tissue

Epidemiology

• hospitalized patients
• elderly, especially nursing home residents
• occurs in 40% of patients who aspirate

Pathology

• large volume pulmonary aspiration of contaminated oral secretions overcome host defenses
• pneumococcal pneumonia arises from pneumococcus colonizing the orophoarynx, but is generally not considered aspiration pneumonia
• most often pulmonary defense systems clear an aspirate without clinical sequellae
• many healthy individuals aspirate episodically without clinical consequences
• pulmonary aspiration of gastric contents
  • may result in Mendelson's syndrome (chemical pneumonitis)
  • proton pump inhibitors (PPIs) may inhibit decontamination of gastric contents
  • increased risk of pneumonia associated with PPIs may be due to aspiration pneumonia from pulmonary aspiration of gastric contents

Clinical manifestations

• patients presenting with aspiration pneumonia have typically been ill for several days
• most commonly 2-5 days after aspiration event
• symptoms develop within days after a sentinel event
• low-grade fever
• malaise
• sputum is generally not malodorous unless process has been present for > 1 week

Laboratory

• complete blood count (CBC)
  • WBC may be increased
• arterial blood gas (ABG) may show increased P(A-a)O2
• sputum for Gram stain
  • mixed bacterial flora with neutrophils
• endotracheal aspiration for culture
  • avoid oral flora
  • generally not indicated
  • mixed aerobic/anaerobic organisms
  • commonly cultured organisms include anaerobes:
    • Prevotella, Fusobacterium nucleatum, Bacteroides, Peptostreptococcus
  • hospitalized patients who aspirate may have mixed flora including enteric Gm- rods
• multiplex PCR assay may be become the new standard

Radiology

• chest X-ray
  • consolidation in dependent pulmonary segments
  • basilar segment of the lower lobes if the patient aspirated while upright or sitting
  • posterior segment of the upper lobe (generally on right side) or the superior segment of the lower lobe is patient aspirated while supine

Complications

• mortality higher than community-acquired pneumonia (29% vs 12%)

• disease interaction(s) of aspiration pneumonia with spontaneous bacterial peritonitis

Differential diagnosis

• aspiration pneumonitis
  • a normal chest X-ray or a complete white-out favors aspiration pneumonitis
  • occurrence within 12-24 hours of vomiting suggests aspiration pneumonitis
• anaerobic lung abscess (foul-smelling sputum)

Management

• evaluation & treatment of etiology of aspiration pneumonia*
  • mixed aerobic/anaerobic organisms
    • clindamycin or penicillin G
    • ceftriaxone + azithromycin
    • fluoroquinolone alone
      • fluoroquinolone + metronidazole
      • adding clindamycin increases risk of C difficile without benefit
    • piperacillin tazobactam + azithromycin for failed fluoroquinolone treatment in an alcoholic
    • extended anaerobic coverage with aminopenicillin/beta-lactamase inhibitor, moxifloxacin, or a combination of clindamycin or metronidazole & ceftriaxone, cefotaxime, or levofloxacin of no mortality benefit, but with increased risk of C difficile colitis
• coverage for hospitalized patients should include:
  • Staphylococcus aureus
  • gram negative bacteria including Pseudomonas aeruginona if cormorbid bacterial peritonitis suspected
    • vancomycin, levofloxacin, aztreonam
    • see Complications: above for cormorbid conditions
• prevention:
  • laryngeal diversion surgery, separating airway from digestive tract [3
  • oral hygiene can reduce risk of aspiration pneumonia (GRS11)
    • Cochrane library concludes low-quality evidence suggests that professional oral care could reduce mortality due to pneumonia in nursing home residents
      • no high-quality evidence identifies most effective oral care measures
  • feeding in upright position not effective
  • feeding tubes do not prevent aspiration pneumonia

* supportive therapy for aspiration pneumonitis

More general terms

• pneumonia (PNA)

Additional terms

• aspiration pneumonitis (Mendelson's syndrome)
• pulmonary aspiration; foreign body aspiration