Lecture Notes on Pneumonia

Introduction

• Discussing pneumonia: inflammation/infection of lung tissue by pathogens (bacterial, viral, fungal).
• Classification based on microbes, acquisition, and location.
• Features and complications.
• Diagnostics and treatment.

Pathophysiology

Mechanisms

1. Aspiration
   • Oropharyngeal: Secretions from oral/nasal cavity aspirated into the airway.
   • Gastric: Gastric contents aspirated into the airway, causing lung tissue damage.
   • Protective reflexes (gag/cough/swallowing) can be compromised by CNS diseases (stroke, seizures, Parkinson's, MS, ALS) or CNS depression (opioids, alcohol, sedation).
2. Inhalation
   • Close contact in crowded environments can lead to infections by pathogens like Mycoplasma, Chlamydia, Influenza, and sometimes Legionella.
   • Legionella associated with contaminated water sources.
3. Environmental Exposure
   • Fungal infections based on geographic location:
     • Coccidioidomycosis: Southwestern USA.
     • Histoplasmosis: Ohio/Mississippi River Valley, associated with bird/bat droppings.
     • Blastomycosis: Eastern USA.
4. Compromised Respiratory Function
   • Impaired mucociliary clearance due to diseases (CF, bronchiectasis) or smoking/COPD.
5. Hematogenous Spread
   • Pathogens spreading via the bloodstream, sometimes seen in IV drug users.
6. Immunocompromised Hosts
   • Patients with conditions like HIV, diabetes, CKD, alcohol use, or those on immunosuppressants.

Microbiology

• Common pathogens:
  • Klebsiella: Particularly in alcoholics.
  • Anaerobes: Often from GI tract, in aspiration cases.
  • Staphylococcus aureus: Post-influenza or IV drug users.
  • Mycoplasma, Chlamydia, Influenza: In crowded settings.
  • Legionella: Water sources.
  • Fungal infections: Location-specific.
  • Pseudomonas: Especially in CF or immunocompromised patients.
  • Streptococcus pneumoniae: Common in community-acquired pneumonia (CAP).

Diagnosis

Features and Complications

• Typical pneumonia: High-grade fevers, rigors, productive cough, hypoxemia, pleuritic chest pain.
• Atypical pneumonia: Upper respiratory symptoms like sore throat, earaches, low-grade fever.
• Consolidative findings:
  • Dull percussion, increased tactile fremitus, positive bronchophony, egophony changes, whispered pectoriloquy.
• Complications: Parapneumonic effusion, empyema, lung abscess, ARDS, sepsis.

Laboratory Testing

• CBC for leukocytosis.
• BMP for acute kidney injury and hyponatremia (possible Legionella).
• Blood and sputum cultures to identify causative organisms.
• Urinary antigens for Strep pneumonia and Legionella.

Imaging

• Chest X-ray: Initial test. Look for patterns:
  • Lobar pneumonia: Consolidation in a single lobe.
  • Bronchopneumonia: Patchy opacities bilaterally.
  • Interstitial pneumonia: Ground-glass opacities, often atypical pathogens.
• CT Scan: If X-ray is inconclusive, or for complicated cases.

Treatment

Antibiotic Regimen

• CAP Outpatient: Macrolide or doxycycline; consider fluoroquinolone if recent antibiotics or comorbidities.
• CAP Inpatient: Respiratory fluoroquinolone or macrolide plus beta-lactam (like Ceftriaxone).
• CAP ICU: Macrolide or fluoroquinolone plus beta-lactam.
• HAP/VAP: Covering for MRSA with Vancomycin and pseudomonas with Piperacillin-tazobactam or Cefepime.
• Aspiration pneumonia: Clindamycin or Augmentin, but often manage like CAP.
• PJP in HIV: Bactrim (trimethoprim-sulfamethoxazole).

Prevention

• Vaccination: Pneumococcal vaccines (PCV 13 and PPSV 23) based on age and risk factors.

Conclusion

• Understanding pneumonia’s pathophysiology, classification, and treatment is crucial for effectively managing patients.