Key Facts

Aspiration pneumonia is a lung infection caused by the inhalation of colonised oropharyngeal or gastric contents into the lower respiratory tract. It should be distinguished from aspiration pneumonitis, which is a chemical inflammatory response to aspirated gastric acid without initial bacterial infection.

Epidemiology

• Accounts for ~5-15% of community-acquired pneumonia cases
• Up to 50% of pneumonias in nursing home residents
• Incidence increases markedly with age (>75 years) and institutional care
• Stroke patients: 30-50% aspirate; ~15-25% of these develop pneumonia

Aetiology

• Mixed oropharyngeal flora: anaerobes (Bacteroides, Fusobacterium, Peptostreptococcus, Prevotella) + aerobes
• Community-acquired: S. pneumoniae, H. influenzae + anaerobes
• Hospital-acquired: Gram-negative bacilli, S. aureus, Pseudomonas + anaerobes
• Poor oral hygiene significantly increases anaerobic load

Pathophysiology

• Aspiration of oropharyngeal secretions colonised with pathogenic bacteria
• Normal protective mechanisms impaired: cough reflex, mucociliary clearance, epiglottic closure
• Gravity-dependent segments affected: right lower lobe (upright), posterior segments of upper lobes (supine)
• Aspiration → chemical pneumonitis (hours) → bacterial superinfection (24-72 hours)
• Necrotising pneumonia may develop with anaerobes → lung abscess → empyema

Typical Presentation

• Cough with foul-smelling purulent sputum (anaerobic infection)
• Fever (may be low-grade initially)
• Breathlessness
• Witnessed aspiration event in some cases
• Usually in context of known risk factor (stroke, altered consciousness, dysphagia)

Clinical Signs

• Signs of consolidation, typically right lower lobe
• Pyrexia
• Tachypnoea, tachycardia
• Reduced SpO₂
• Poor dentition (significant risk factor)

Aspiration Pneumonitis vs Pneumonia

• Pneumonitis (Mendelson syndrome): acute chemical lung injury from gastric acid; rapid onset (hours), diffuse bilateral crackles, self-limiting in ~48-72 hours without antibiotics
• Pneumonia: bacterial infection; slower onset (24-72 hours post-aspiration), localised consolidation, purulent sputum

Red Flags

• Lung abscess (non-resolving consolidation, air-fluid level on CXR)
• Empyema
• Rapidly progressive necrotising pneumonia
• Recurrent aspiration events
• Inability to protect airway

Bedside

• Pulse oximetry: assess oxygenation
• ABG: if SpO₂ <92%
• SALT assessment: swallowing evaluation to prevent recurrence

Bloods

• FBC: leucocytosis
• CRP: elevated
• U&Es: renal function, hydration status
• Blood cultures: before antibiotics in moderate-severe
• Procalcitonin: distinguish pneumonitis from pneumonia

Imaging

• Chest X-ray: consolidation (typically right lower lobe), air-fluid level (abscess)
• CT chest: if abscess suspected, non-resolving, or to guide drainage

Special Tests

• Sputum MC&S: anaerobic and aerobic cultures
• Bronchoscopy: if foreign body suspected or non-resolving
• Video fluoroscopy/FEES: formal swallowing assessment
• Barium swallow: if oesophageal pathology or fistula suspected

Non-pharmacological

• Nil by mouth until SALT assessment
• Positioning: sit upright (30-45° head-of-bed elevation)
• Oral hygiene: regular mouth care, dental assessment
• Oxygen therapy (target SpO₂ 94-98%)
• IV fluids if nil by mouth or dehydrated
• NG tube feeding only after SALT assessment (NG tubes themselves increase aspiration risk)

Pharmacological

Antibiotics (must cover anaerobes):

• Co-amoxiclav 1.2g IV TDS (covers aerobes + anaerobes) — first-line
• Or amoxicillin 1g IV TDS + metronidazole 500mg IV TDS
• Penicillin allergy: clindamycin 600mg IV QDS or moxifloxacin 400mg OD
• Hospital-acquired aspiration: piperacillin-tazobactam 4.5g IV TDS
• Duration: 7-14 days (longer for abscess/empyema — up to 4-6 weeks)

Lung abscess:

• Prolonged antibiotics (4-6 weeks minimum)
• Co-amoxiclav or piperacillin-tazobactam
• CT-guided percutaneous drainage if >6cm or failed medical therapy

Surgical/Interventional

• Chest drain for empyema
• CT-guided drainage for lung abscess
• Tracheostomy for patients with recurrent aspiration and inability to protect airway
• PEG feeding: consider for chronic dysphagia (though does not eliminate aspiration risk)

Referral Criteria

• SALT assessment for all patients with aspiration pneumonia
• Respiratory referral for recurrent aspiration or lung abscess
• ENT/gastroenterology for structural causes of aspiration
• Palliative care if aspiration due to end-stage neurological disease

• Mortality: ~20-30% for hospitalised aspiration pneumonia
• Higher mortality in elderly, nursing home residents, and mechanically ventilated patients
• Lung abscess mortality: ~5-10% with appropriate treatment
• Recurrence rate is high (~30%) without addressing underlying cause
• Chronic aspiration leads to progressive lung damage and bronchiectasis
• Outcomes improve with early SALT assessment and dysphagia management

Risk Factors for Aspiration

Aspiration Pneumonitis vs Pneumonia