Aspiration Pneumonia

Source: Fishman's Pulmonary Diseases and Disorders, 2-Volume Set & Murray & Nadel's Textbook of Respiratory Medicine

1. Definition

• Fishman's Pulmonary Diseases and Disorders, block14, p.1198

2. Etiology

Microbiology

• Fishman's, block14, p.1200

Risk Factors for Aspiration

• Cerebrovascular disease (ischemic/hemorrhagic stroke, subarachnoid hemorrhage) - dysphagia in 40-70% of acute stroke patients
• Parkinson's disease (dysphagia in 52-82%)
• Alzheimer's disease (dysphagia in 84%)
• Multiple sclerosis, motor neuron disease
• Brainstem tumors/lesions

• Head and neck cancers, post-surgical states
• Esophageal disorders (achalasia, strictures, diverticula, GERD)
• Scleroderma (esophageal dysmotility, decreased LES pressure, hiatal hernia)
• Polymyositis-dermatomyositis (inflammatory myositis of hypopharynx and upper esophagus)

• Sedatives, opioids, antipsychotics (phenothiazines, haloperidol impair swallow coordination)
• Anticholinergic drugs (dry secretions, impair swallowing)
• Alcohol abuse
• Proton pump inhibitors (increase gastric/oropharyngeal colonization with pathogens)

• Nursing home/long-term care residence
• Poor oral hygiene (dental plaque as reservoir of pathogens)
• 10 or more periodontal pockets = increased pneumonia mortality

• Fishman's, block14, Table 69-3, pp.1199-1200; Murray & Nadel's, block9, pp.942-944

3. Pathogenesis

Normal Defense Mechanisms

• Forceful coughing reflex
• Active ciliary mucociliary transport
• Normal humoral and cellular immune mechanisms

When Defense Fails

1. Oropharyngeal colonization - The elderly show increased colonization with S. aureus, aerobic gram-negative bacilli (Klebsiella, E. coli). This may be transient but is potentiated by poor oral hygiene and dental plaque.
2. Aspiration of colonized secretions - Volume of the aspirate directly correlates with pneumonia risk (demonstrated in stroke patients undergoing swallow evaluation).
3. Dysphagia - The major predisposing factor. Swallowing requires 5 cranial nerves, 50+ muscles, bilateral sensorimotor cortex input, and brainstem medullary swallowing center. Disruption at any level causes aspiration.
4. Impaired cough reflex - Substance P (released from vagal sensory nerves in pharynx/upper airways) mediates the cough reflex. ACE breaks down substance P. In elderly patients with pneumonia, sputum substance P levels are markedly reduced. The greater the cough reflex derangement, the greater the pneumonia risk.
5. Dependent lung segment inoculation - The inoculum settles gravitationally into the posterior upper lobe segments (recumbent) or basal lower lobe segments (upright/semirecumbent), triggering an inflammatory response leading to consolidation.
6. Increased bacterial load - Proton pump inhibitors raise gastric pH, allowing gastric bacterial overgrowth and subsequent oropharyngeal colonization. Periodontal disease provides a reservoir of gram-negative and anaerobic organisms.

• Fishman's, block14, pp.1198-1200; Murray & Nadel's, block9, pp.942-944

4. Clinical Features

Symptoms

• Fever, cough with purulent sputum
• Dyspnea/shortness of breath
• The presentation is often indistinguishable from ordinary CAP

• Presence of risk factors for dysphagia/aspiration
• Infiltrate in a dependent bronchopulmonary segment - if aspirated recumbent: posterior segments of upper lobes and apical segments of lower lobes; if aspirated upright/semirecumbent: basal segments of lower lobes
• Silent aspiration is common - aspiration episode is typically unwitnessed

Populations at Highest Risk

• Elderly (risk of pneumonia is 6x higher in those over 75 vs. <60 years)
• Nursing home/residential care residents (highest attack rate)
• Post-stroke patients
• Patients with neurologic degenerative diseases

Complications (if untreated/severe)

1. Lung abscess - Higher incidence than in standard CAP; occurs especially with anaerobic organisms and periodontal disease
2. Cavitation - Complicates necrotizing pneumonia
3. Empyema - Parapneumonic collections should be drained immediately and sent for culture
4. ARDS - In severe or bilateral aspiration
5. Diffuse aspiration bronchiolitis (DAB) - Chronic, recurrent aspiration causing diffuse centrilobular nodules with tree-in-bud pattern on CT; associated with GERD and neurologic impairment; can lead to bronchiectasis
6. Higher mortality compared to non-aspiration CAP
7. Longer hospital stay and higher risk of recurrence than CAP

• Fishman's, block14, p.1199-1200; Murray & Nadel's, block9, p.943-944

5. Diagnosis

Diagnostic Criteria

• Clinical features compatible with pneumonia (fever, dyspnea, purulent sputum)
• Radiographic infiltrate in a characteristic dependent bronchopulmonary segment
• No witnessed aspiration episode is required (and is usually absent)

Chest Radiograph

• Infiltrate/consolidation in a dependent segment (as described above)
• Cavitation may be visible in advanced/necrotizing disease
• Right-sided predominance (due to the more vertical right main bronchus)

CT Findings (from Murray & Nadel's)

• Posterior opacities (hallmark)
• Focal, peripheral, or peribronchiolar consolidation involving one or more segments (contrasted with lobar pattern of typical pneumonia)
• Lung abscess (Fig. 4.3.2C in Murray & Nadel's)
• Empyema with interlobular septal thickening and ground-glass opacities

Laboratory

• Leukocytosis (non-specific)
• Sputum culture (limited yield due to oropharyngeal contamination)
• Protected quantitative bronchial sampling - the most rigorous microbiological method (El-Solh et al.): identifies gram-negative enteric bacteria as predominant organisms
• Procalcitonin - may have diagnostic utility in distinguishing aspiration pneumonitis from pneumonia (El-Solh AA et al., Crit Care Med 2011)

Swallowing Evaluation

• Videofluoroscopic swallow study (VFSS) - gold standard; directly visualizes aspiration
• Fiberoptic endoscopic evaluation of swallowing (FEES)
• Bedside assessment of cough and gag reflex is unreliable for screening

Pathology (Murray & Nadel's)

• Pulmonary alveolar septal thickening from type 2 pneumocyte hyperplasia
• Increased macrophages and organizing pneumonia within airspaces
• Vegetable matter may be visible on biopsy
• Fishman's, block14, p.1200; Murray & Nadel's, block9, p.944

6. Treatment

A. Antibiotic Therapy (with Drug Dosages)

• Setting: community vs. healthcare facility
• Patient characteristics: alcoholism, oral hygiene, injection drug use, recent antibiotics or acid-suppressive therapy

• Amoxicillin-clavulanate 875/125 mg PO twice daily (preferred oral agent with anaerobic coverage)
• OR Clindamycin 300-450 mg PO three times daily (if penicillin allergy, for anaerobic coverage)
• Fluoroquinolone (respiratory): Levofloxacin 750 mg PO/IV once daily

• Ceftriaxone 1-2 g IV once daily
• Piperacillin-tazobactam 3.375-4.5 g IV every 6-8 hours (broad gram-negative and anaerobic coverage)
• Levofloxacin 750 mg IV/PO once daily, OR Moxifloxacin 400 mg IV/PO once daily
• Ertapenem 1 g IV once daily (if carbapenem indicated)
• Imipenem 500 mg IV every 6 hours (severe/healthcare-associated)

• Vancomycin 15-20 mg/kg IV every 8-12 hours (target trough 15-20 mcg/mL)
• OR Linezolid 600 mg IV/PO every 12 hours

• Periodontal disease
• Putrid (foul-smelling) sputum
• Necrotizing pneumonia or lung abscess on chest radiograph
• Clindamycin 600-900 mg IV every 8 hours (or 300-450 mg PO TID) - drug of choice for anaerobic lung infection
• Metronidazole 500 mg IV/PO every 8 hours (in combination; poor monotherapy for lung anaerobes)
• Piperacillin-tazobactam or ampicillin-sulbactam 3 g IV every 6 hours also cover anaerobes

• Standard CAP equivalent: 5-7 days (no evidence for longer courses)
• Exception: Lung abscess requires prolonged therapy (4-6 weeks)
• Pleural collections: drain immediately + culture
• Fishman's, block14, pp.1200-1201

B. Management of Dysphagia (Reduction of Aspiration Risk)

• Aspiration risk is maximal with water/thin fluids (20 Pa.s)
• Nectar-thick liquids (270 Pa.s) and pudding-thick (3900 Pa.s) substantially reduce aspiration
• Videofluoroscopy guides the appropriate viscosity prescription

• Chin-down posture - widens valleculae and narrows the laryngeal inlet
• Hard/effortful swallow, breath-hold during swallow, planned cough after swallow
• Head turn to affected side (directs bolus away from weakened side)

• Masako maneuver (strengthens base of tongue)
• Shaker exercise (head lift; strengthens suprahyoid muscles)
• Lingual resistance exercises

• Short-term nasogastric tube for severe dysphagia with likely recovery
• PEG tube for prolonged dysphagia
• The FOOD trials showed early tube feeding reduced mortality by 5.8% absolute in dysphagic stroke patients

C. Oral Hygiene

• Regular tooth brushing after each meal
• Weekly dental care (shown in one RCT of nursing home residents to reduce pneumonia regardless of dentition status)
• "Tongue cleaning" reduces oropharyngeal bacterial load even in edentulous patients

D. Pharmacologic Prevention

• ACE inhibitors - reduce breakdown of substance P, enhance cough reflex and swallow sensation. Multiple studies show reduced risk of aspiration pneumonia in stroke patients. Lipophilic ACE inhibitors may be more effective. A UK population-based study showed ACE inhibitors reduced pneumonia risk (OR 0.75; 95% CI 0.65-0.86).
• Avoid: sedatives, phenothiazines, haloperidol (impair swallowing coordination), anticholinergics (dry secretions, impair swallowing), PPIs when not clinically indicated (increase oropharyngeal colonization)
• Nicergoline (ergot alkaloid) - upregulates substance P; comparable efficacy to ACE inhibitors in preliminary studies
• Fishman's, block14, pp.1200-1202; Murray & Nadel's, block9, pp.947-950

7. Complications Summary

• Fishman's, block14, pp.1200-1202; Murray & Nadel's, block9, pp.943-947

Key Distinction: Aspiration Pneumonia vs. Aspiration Pneumonitis

Classification of Aspiration Syndromes - Fishman's Pulmonary Diseases and Disorders

Level 1: Classification by Nature of the Inoculum (Table 127-4, Chapter 127)

1. Chemical Pneumonitis (Aspiration Pneumonitis / Mendelson's Syndrome)

• Phase 1 (within 1 hour): Direct caustic acid injury to pulmonary tissue
• Phase 2 (peaks 4-6 hours): Neutrophil recruitment; release of reactive oxygen species (ROS) and proteases via NADPH oxidase; NF-κB activation; cytokine release (TNF-α, IL-1β, IL-8)

2. Bacterial Infection (Aspiration Pneumonia)

3. Airway Obstruction (Foreign Body / Particulate Aspiration)

• Fishman's, Chapter 127 (block26), Table 127-4, p.2238

Level 2: Full Classification of Aspiration-Related Pulmonary Disorders (Chapter 69)

Major Syndromes (Distinct Clinical Entities):

• Chemical pneumonitis from sterile gastric acid aspiration
• Occurs ONLY in patients with markedly depressed level of consciousness (drug overdose, seizures, coma, anesthesia)
• Treatment: largely supportive

• Infectious process from aspiration of oropharyngeal secretions colonized by pathogenic bacteria
• Occurs in patients with dysphagia and impaired swallowing
• Treatment: antibiotics (essential)

• Result of chronic, recurrent occult aspiration of foreign matter (food particles)
• Associated with GERD, esophageal dysmotility, neurologic impairment
• CT: diffuse centrilobular nodules with tree-in-bud pattern
• Treatment: macrolides reduce acute exacerbations

Other Aspiration Syndromes (also listed in Chapter 69):

• Fishman's, Chapter 69 (block14), Introduction, pp.1195-1196

The Key Comparative Classification Table (Table 69-1, Chapter 69)

• Fishman's, Chapter 69 (block14), Table 69-1, p.1195-1196

Summary Diagram

ASPIRATION
    │
    ├── By INOCULUM (Table 127-4):
    │       ├── Acid/chemical → Chemical Pneumonitis (Mendelson's)
    │       ├── Bacteria → Aspiration Pneumonia
    │       └── Particulate → Airway Obstruction
    │
    └── By CLINICAL SYNDROME (Chapter 69):
            ├── Aspiration Pneumonitis (acute, chemical)
            ├── Aspiration Pneumonia (infectious)
            ├── Diffuse Aspiration Bronchiolitis (chronic, recurrent)
            ├── Lung Abscess
            ├── Exogenous Lipoid Pneumonia
            ├── Chronic Interstitial Fibrosis
            └── M. fortuitum Pneumonia