Overview
This lecture explains pneumonia, its causes, types, diagnostic features, and treatments, focusing on pathophysiology, microbial causes, and clinical classification.
Pneumonia Pathophysiology
- Pneumonia is a lung infection causing inflammation and fluid in lung tissue, making breathing harder.
- Air travels via trachea → bronchi → bronchioles → alveoli, where gas exchange occurs.
- The immune system protects lungs with coughing, mucociliary escalator, and alveolar macrophages.
- Pathogens overcoming these defenses colonize lung tissue, causing an inflammatory response with fluid and white blood cell influx.
Causes of Pneumonia
- Most common causes are viruses (e.g., influenza), bacteria (e.g., Streptococcus pneumoniae, Haemophilus influenzae, Staphylococcus aureus), and less commonly fungi and mycobacteria.
- Atypical pneumonia is caused by organisms like Mycoplasma pneumoniae and Chlamydophila pneumoniae, causing milder or vague symptoms.
- Fungal causes include Coccidioidomycosis, Histoplasmosis, Blastomycosis (regional), Cryptococcus (widespread), and Pneumocystis jirovecii (immunocompromised).
- Mycobacterium tuberculosis (TB) is an important slow-growing bacterial cause.
Types of Pneumonia by Acquisition
- Community-acquired pneumonia: contracted outside hospitals.
- Hospital-acquired (nosocomial) pneumonia: develops during hospitalization; microbes are often antibiotic-resistant (e.g., MRSA).
- Ventilator-associated pneumonia: a subset of hospital-acquired, linked to biofilm formation on endotracheal tubes.
- Aspiration pneumonia: from inhaling food, drink, or gastric contents, often when cough/gag reflexes are impaired.
Types of Pneumonia by Location
- Bronchopneumonia: infection spread throughout bronchioles and alveoli.
- Atypical/interstitial pneumonia: infection mainly in interstitium around alveoli.
- Lobar pneumonia: infection consolidates an entire lobe, commonly from Streptococcus pneumoniae.
Lobar Pneumonia Stages
- Congestion (1-2 days): fluid fills alveoli and vessels.
- Red hepatization (3-4 days): airspaces fill with exudate, red blood cells, neutrophils, and fibrin.
- Gray hepatization (5-7 days): breakdown of red blood cells changes color; lungs remain firm.
- Resolution (day 8+): exudate is cleared by enzymes, macrophages, or coughing.
Clinical Features and Diagnosis
- Common symptoms: shortness of breath, chest pain, productive cough, fatigue, and fever.
- Chest x-ray: bronchopneumonia shows patchy infiltrates, interstitial pneumonia shows reticular opacities, lobar pneumonia is localized.
- Physical findings: dullness to percussion, increased tactile vocal fremitus, late inspiratory crackles, bronchial breath sounds, bronchophony, and egophony.
Treatment
- Most cases treated with antibiotics for bacterial causes.
- Symptomatic relief with cough suppressants and pain medication.
Key Terms & Definitions
- Alveoli — tiny lung sacs enabling oxygen and carbon dioxide exchange with blood.
- Mucociliary escalator — airway lining that traps and moves particles out of lungs.
- Macrophages — immune cells in alveoli that ingest microbes.
- Community-acquired pneumonia — infection acquired outside healthcare settings.
- Nosocomial pneumonia — pneumonia developed during hospital stay.
- MRSA — methicillin-resistant Staphylococcus aureus, an antibiotic-resistant bacteria.
- Ventilator-associated pneumonia — pneumonia developing in patients on mechanical ventilation.
- Aspiration pneumonia — pneumonia from inhaled foreign material.
- Lobar pneumonia — infection consolidates an entire lung lobe.
Action Items / Next Steps
- Review stages and types of pneumonia.
- Familiarize with key causative microbes and diagnostic features.
- Prepare for related exam questions on classification and pathophysiology.