Aspiration Pneumonia

• Glenn G. Fort, M.D., M.P.H.

 Basic Information

Definition

Aspiration pneumonia is a vague term that refers to pulmonary abnormalities following abnormal entry of endogenous or exogenous substances in the lower airways. It is generally classified as:

1. •

   Aspiration (chemical pneumonitis)

2. •

   Primary bacterial aspiration pneumonia

3. •

   Secondary bacterial infection of chemical pneumonitis

Synonyms

1. Pneumonia, aspiration

ICD-10CM CODES
J69.0	Pneumonitis due to inhalation of food and vomit

Epidemiology & Demographics

Incidence (In U.S.)

1. •

   20% to 35% of all pneumonias.

2. •

   5% to 15% of all community-acquired pneumonias.

Peak Incidence

Elderly patients in hospitals or nursing homes.

Prevalence (In U.S.)

Unknown (unreliable data).

Predominant Sex

Males and females affected equally.

Predominant Age

Elderly.

Physical Findings & Clinical Presentation

1. •

   Shortness of breath, tachypnea, cough, sputum, fever after vomiting, or difficulty swallowing.

2. •

   Rales, rhonchi, often diffusely throughout lung.

Etiology

Complex interaction of etiologies, ranging from chemical (often acid) pneumonitis after aspiration of sterile gastric contents (generally not requiring antibiotic treatment) to bacterial aspiration. Table 1 summarizes risk factors for aspiration pneumonia.

Community-acquired aspiration pneumonia

1. •

   Generally results from predominantly anaerobic mouth bacteria (anaerobic and microaerophilic streptococci, fusobacteria, gram-positive anaerobic nonspore-forming rods), Bacteroides species (melaninogenicus, intermedius, oralis, ureolyticus), Haemophilus influenzae, and Streptococcus pneumoniae

2. •

   Rarely caused by Bacteroides fragilis (of uncertain validity in published studies) or Eikenella corrodens

3. •

   High-risk groups: the elderly; alcoholics; IV drug users; patients who are obtunded; stroke victims; and those with esophageal disorders, seizures, poor dentition, or recent dental manipulations.

Hospital-acquired aspiration pneumonia

1. •

   Often occurs among elderly patients and others with diminished gag reflex; those with nasogastric tubes, intestinal obstruction, or ventilator support; and especially those exposed to contaminated nebulizers or unsterile suctioning.

2. •

   High-risk groups: seriously ill hospitalized patients (especially patients with coma, acidosis, alcoholism, uremia, diabetes mellitus, nasogastric intubation, or recent antimicrobial therapy, who are frequently colonized with aerobic gram-negative rods); patients undergoing anesthesia; those with strokes, dementia, or swallowing disorders; the elderly; and those receiving antacids or H₂ blockers (but not sucralfate).

3. •

   Hypoxic patients receiving concentrated O₂ have diminished ciliary activity, encouraging aspiration.

4. •

   Causative organisms:

   1. 1.

      Anaerobes listed above, although in many studies gram-negative aerobes (60%) and gram-positive aerobes (20%) predominate.

   2. 2.

      E. coli, P. aeruginosa, S. aureus including MRSA, Klebsiella, Enterobacter, Serratia, Proteus spp., H. influenzae, S. pneumoniae, Legionella, and Acinetobacter spp. (sporadic pneumonias) in two thirds of cases.

   3. 3.

      Fungi, including Candida albicans, in <1%.

Diagnosis

Differential Diagnosis

1. •

   Other necrotizing or cavitary pneumonias (especially tuberculosis, gram-negative pneumonias).

2. •

   See “Pulmonary Tuberculosis.”

Workup

1. •

   Chest x-ray.

2. •

   Complete blood count (CBC), blood cultures.

3. •

   Sputum Gram stain and culture.

4. •

   Consideration of tracheal aspirate.

Laboratory Tests

1. •

   CBC: leukocytosis often present.

2. •

   Sputum Gram stain.

   1. 1.

      Often useful when carefully prepared immediately after obtaining suctioned or expectorated specimen, examined by experienced observer.

   2. 2.

      Only specimens with multiple white blood cells and rare or absent epithelial cells should be examined.

   3. 3.

      Unlike nonaspiration pneumonias (e.g., pneumococcal), multiple organisms may be present.

   4. 4.

      Long, slender rods suggest anaerobes.

   5. 5.

      Sputum from pneumonia caused by acid aspiration may be devoid of organisms.

   6. 6.

      Cultures should be interpreted in light of morphology of visualized organisms.

Imaging Studies

1. •

   Chest x-ray often reveals bilateral, diffuse, patchy infiltrates and posterior segment upper lobes (Fig. 1). Chemical pneumonitis typically affects the most dependent regions of the lungs.

   

2. •

   Aspiration pneumonia of several days’ or longer duration may reveal necrosis (especially community-acquired anaerobic pneumonias) and even cavitation with air-fluid levels, indicating lung abscess.

Treatment

Nonpharmacologic Therapy

1. •

   Airway management to prevent repeated aspiration.

2. •

   Ventilatory support if necessary.

Acute General Rx

Acute aspiration of acidic gastric contents without bacteria may not require antibiotic therapy; consult infectious disease or pulmonary expert.

1. •

   Community-acquired anaerobic aspiration pneumonia: clindamycin (600 mg IV twice daily followed by 300 mg q6h orally). Intravenous penicillin G (1 to 2 million U q4 to 6h) can also still be used. Alternative oral agents include: amoxicillin-clavulanate (875 mg orally twice daily), amoxicillin plus metronidazole or oral moxifloxacin (400 mg orally once daily). Do not use metronidazole alone, as this is associated with high failure rates.

2. •

   Nursing home aspirations: levofloxacin 500 to 750 mg qd or piperacillin-tazobactam 3.375 g q6h or cefepime 2 g q8h ± vancomycin if MRSA suspected or known.

3. •

   Hospital-acquired aspiration pneumonia:

   1. 1.

      Piperacillin-tazobactam 3.375 g IV q6h, or meropenem 1 g IV q 8h ± vancomycin IV to cover MRSA. Alternative agents are ceftriaxone 2 g IV q24h plus metronidazole 500 mg IV q8h.

   2. 2.

      Knowledge of resident flora in the microenvironment of the aspiration within the hospital is crucial to intelligent antibiotic selection; consult infection control nurses or hospital epidemiologist.

   3. 3.

      Confirmed Pseudomonas pneumonia should be treated with antipseudomonal beta-lactam agent (piperacillin/tazobactam, cefepime) plus an aminoglycoside until antimicrobial sensitivities confirm that less toxic agents may replace the aminoglycoside.

   4. 4.

      Do not use metronidazole alone for anaerobes.

Disposition

Repeat chest x-ray in 6 to 8 wk in most patients.

Referral

For consultation with infectious disease and/or pulmonary experts for patients with respiratory distress, hypoxia, ventilatory support, pneumonia in more than one lobe, or necrosis or cavitation on x-ray examination or for those not responding to antibiotic therapy within 2 to 3 days.

Suggested Readings

• E. Daoud, J. Guzman: Are antibiotics indicated for the treatment of aspiration pneumonia?. Cleve Clin J Med. 77 (9):573 2010 20810867

• D.M. DiBardino, R.G. Wunderink: Aspiration pneumonia: a review of modern trends. J Crit Care. 30:40–48 2015 25129577

• S. Teramoto, et al.: Update on the pathogenesis and management of pneumonia in the elderly-roles of aspiration pneumonia. Respir Investig. 53:178–184 2015 26344607

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1. Aspiration Pneumonia (Patient Information)