Pneumonia Lecture Notes

Introduction

• Pneumonia is an infection in one or both lungs causing inflammation in the alveoli.
• Alveoli are filled with fluid or pus, making it difficult to breathe.
• Defined as inflammation and consolidation of lung tissue due to an infectious agent.

Pathogenesis

• Normally, the body filters organisms to prevent lung infections.
• Infection occurs if the immune system is weak, the organism is strong, or the body fails to filter organisms.

Risk Factors

• Cigarette smoking, upper respiratory tract infections, alcohol, corticosteroid therapy, old age, recent influenza infection, pre-existing lung disease.
• Reduced host defenses, reduced immune defenses (corticosteroid treatment, diabetes, malignancy), reduced cough reflex, disordered mucociliary clearance, bulbar or vocal cord palsy.
• Aspiration of nasopharyngeal or gastric secretions, immobility, endotracheal intubation, infections from medical devices.

Pathology

• Congestion: Presence of proteinaceous exudate and bacteria in alveoli.
• Red Hepatization: Erythrocytes and neutrophils present in alveolar exudate.
• Gray Hepatization: Erythrocytes lysed, neutrophils predominant, bacteria disappeared.
• Resolution: Macrophages clear debris.

Types of Pneumonia

• Anatomical Classification:
  • Bronchopneumonia: affects lung patches around bronchi.
  • Lobar pneumonia: involves a single lobe of a lung.
  • Interstitial pneumonia: involves areas between alveoli.
• Clinical Classification:
  • Community-Acquired Pneumonia (CAP).
  • Nosocomial Pneumonia: HAP (Hospital), VAP (Ventilator), HCAP (Health Care Associated).
  • Pneumonia in Immunocompromised hosts.

Etiology

• Bacterial, viral, mycobacterial, fungal, parasitic.
• Streptococcus pneumoniae is the most common cause globally.

Clinical Features

• General symptoms: high fever, productive cough, pleuritic chest pain, breathlessness.
• Additional symptoms: sharp chest pain, headache, excessive sweating, loss of appetite, confusion.

Signs of Consolidation

• Dull percussion, bronchial breath sounds, crackles, increased vocal/resonance, pleural rub.

Investigations

• Sputum Tests: Gram staining, culture.
• Imaging: X-ray shows homogenous opacity, CT thorax seldom used.
• Blood Tests: Complete blood count, electrolytes, blood culture.
• Other Tests: Bacterial antigen, serological, molecular tests, C-reactive protein.

Treatment

• Outpatients: Macrolide antibiotics for healthy individuals; fluoroquinolones or beta-lactams for those with comorbidities.
• Inpatients (Non-ICU): Respiratory fluoroquinolone or beta-lactam plus macrolide.
• ICU Patients: Beta-lactam plus azithromycin or fluoroquinolone.
• Specific Cases: Antipseudomonal beta-lactams for Pseudomonas, linezolid or vancomycin for MRSA.

Complications

• Lung abscess, para-pneumonic effusions, empyema, sepsis, ARDS, respiratory failure, multi-organ failure.

Prevention

• Smoking cessation, better nutrition, respiratory hygiene, vaccines (pneumococcal, influenza).

Conclusion

• Chest radiograph infiltrate is considered the gold standard for pneumonia diagnosis.
• Initial treatment regimens for CAP are often empiric.
• Mortality rates for CAP are low in ambulatory patients but higher for those hospitalized.

Additional Notes

• Pneumonia can be life-threatening, particularly in severe cases or when associated with complications like multi-organ failure.
• Empiric treatment is often used due to the varied microbial causes and presentations of pneumonia.