Lung injury from inhaled oropharyngeal or gastric contents — chemical vs infectious.
Also known as: aspiration pneumonia, aspiration pneumonitis, Mendelson syndrome, anaerobic pneumonia
Overview
Aspiration pneumonitis: acute lung injury after inhalation of sterile gastric contents (chemical). Aspiration pneumonia: infectious pneumonia from aspirated oropharyngeal flora colonizing distal airways.
Epidemiology
Common in elderly, stroke patients, and those with neurologic disease. Accounts for ~10% of CAP in older adults. Increased in nursing home residents, post-operative patients, and those with dysphagia.
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Chemical pneumonitis: aspirated gastric acid (pH <2.5) damages alveolar epithelium → rapid-onset inflammation, edema, hypoxemia. Aspiration pneumonia: bacterial colonization of aspirated material leads to infection over 24-72 h. Predominantly dependent lung segments — superior segment of lower lobes (supine) or posterior segment of upper lobes/RML (lateral recumbent). Microbiology: streptococci, S. aureus, gram-negatives, and anaerobes; anaerobic role has been overstated.
Clinical presentation
Symptoms
Witnessed aspiration event, choking, or coughing during meals
Cough (may be productive), dyspnea, wheeze
Chemical pneumonitis: acute respiratory distress within minutes-hours of aspiration
Pneumonia: subacute fever, productive cough, foul-smelling sputum (especially with anaerobes/abscess)
Signs / physical exam
Tachypnea, hypoxia, fever
Crackles or bronchial breath sounds in dependent segments
Halitosis with anaerobic infection or abscess
Classic findings
Infiltrate in posterior segment of upper lobe or superior segment of lower lobe (supine aspiration); right side more common (more vertical right main bronchus).
Differential diagnosis
Community-acquired pneumonia — No witnessed aspiration; non-dependent distribution; typical pathogens
Lung abscess — Cavitary lesion with air-fluid level, foul-smelling sputum, indolent course over weeks
ARDS from non-aspiration cause — Sepsis, trauma, pancreatitis — bilateral infiltrates, PaO2/FiO2 ≤300
Foreign body aspiration — Sudden choking episode; focal hyperinflation or atelectasis; bronchoscopy diagnostic and therapeutic
Exogenous lipoid pneumonia — History of mineral oil ingestion or vaping; low attenuation on CT
Diagnostic workup
Labs
CBC, BMP, lactate, blood cultures (if pneumonia)
Sputum Gram stain/culture; anaerobic culture rarely useful given oropharyngeal contamination
Imaging
CXR — infiltrate in gravity-dependent segments; bilateral if large volume
CT chest if abscess, empyema, or non-resolution; identifies cavitation, foreign body
Bronchoscopy if obstructing foreign body suspected
Other studies
Swallow evaluation (video fluoroscopic swallow study or fiberoptic endoscopic evaluation of swallowing) after stabilization, especially post-stroke
Modified barium swallow to characterize aspiration risk and guide dietary/feeding strategy
Diagnostic algorithm
Feature
Pneumonitis (Chemical)
Pneumonia (Infectious)
Time course
Minutes-hours
Days
Cause
Sterile gastric acid
Oropharyngeal bacteria
Sputum
Frothy, non-purulent
Purulent, ± foul-smelling
Resolution
24-48 h with support
Requires antibiotics × 5-7 days
Antibiotics
Usually not needed
Beta-lactam ± anaerobic coverage if abscess
Aspiration pneumonitis vs aspiration pneumonia — clinical features and management contrast.
Treatment
First-line
Aspiration pneumonitis (chemical, witnessed, no infection signs): supportive care — supplemental O2, suctioning, observation. Do NOT routinely give antibiotics; many resolve in 24-48 h.
Aspiration pneumonia (community-onset, non-severe): ampicillin-sulbactam 1.5-3 g IV q6h OR amoxicillin-clavulanate 875 mg PO BID; alternative: respiratory fluoroquinolone (moxifloxacin) or doxycycline
Severe community aspiration pneumonia: piperacillin-tazobactam or ceftriaxone + metronidazole (if severe periodontal disease or putrid sputum); add MRSA coverage if risk factors
Hospital-acquired aspiration: cover MRSA + Pseudomonas as for HAP/VAP — piperacillin-tazobactam, cefepime, meropenem ± vancomycin/linezolid
Persuasive recent data: routine anaerobic coverage often unnecessary unless lung abscess, empyema, necrotizing pneumonia, or severe periodontal disease
Second-line / adjunct
Lung abscess: prolonged antibiotics 3-6 weeks until cavity resolves or stable scar; surgical/percutaneous drainage if no response after 4-6 weeks
Empyema or complicated parapneumonic effusion: chest tube ± intrapleural tPA/DNase
Address underlying aspiration risk: speech-language pathology, diet modification, swallow rehab, elevation of head of bed, dental care, reflux management
Tube feeding (PEG, NG) does NOT reliably prevent aspiration in advanced dementia
Complications
Lung abscess, empyema
ARDS, respiratory failure
Recurrent aspiration, chronic pneumonitis
Bronchiectasis from repeated injury
Bronchopleural fistula, necrotizing pneumonia
PANCE pearls
Distinguishing pneumonitis (chemical, 24-h resolution) from pneumonia (bacterial, persistent) determines whether antibiotics are needed.
Right lower lobe (especially superior segment) and right middle lobe are favored sites due to bronchial anatomy in supine patients.
Modern data downplay routine anaerobic coverage — reserve clindamycin or metronidazole add-on for clear abscess, empyema, putrid sputum, or severe periodontal disease.
PEG tube placement does not reduce aspiration pneumonia or mortality in advanced dementia.
Following a stroke, a formal swallow evaluation before any oral intake reduces pneumonia incidence.
References
ATS/IDSA 2019 CAP — Diagnosis and Treatment of Adults with Community-acquired Pneumonia (Metlay et al., Am J Respir Crit Care Med 2019)
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