PNEUMONIA- Its Etiology, Pathophysiology, Classification and Severity Assessment Method!

 PNEUMONIA

Definition:

"Pneumonia is an infection of pulmonary parenchyma". (Harrison)

                                                   OR

"Pneumonia is defined as an acute respiratory illness associated with recently developed radiological pulmonary shadowing which may be segmental, lobar or multilobar". (Davidson)

Etiology:

• Microorganisms gain excess to the lower respiratory tract in several ways:

1. Aspiration from the oropharynx (most common).
2. Inhalation of contaminated droplets.
3. Hematogenous spread.
4. Contiguous extension.

Pathophysiology of Pneumonia:

• Pneumonia results from proliferation of microbial pathogens at the alveolar level and the hosts response to these microorganisms. 

Defensive Mechanisms against Pneumonia:

• The defensive mechanism against pneumonia involve:

1. Branching architecture of tracheobronchial tree.
2. Muco-ciliary clearance.
3. Local antibacterial factors.
4. Gag Reflex.
5. Cough mechanism.
6. Normal flora adhering to mucosal cells of oropharynx.
7. Alveolar macrophages, local proteins

• The alveolar macrophages initiate the inflammatory response to strengthen the lower respiratory tract defenses.

IL-1 & TNF (Tumor necrosis factor) -- Fever

IL-8 release and attraction of neutrophil to lungs -- Peripheral leukocytosis.

Inflammatory mediators (Macrophages and Neutrophils) -- Localized alveolar capillary leak

Stages of Pneumonia:

1. Oedematous phase:

• Alveoli filled with proteinaceous exudate and bacteria.
• Rapidly followed by red hepatization phase

      2. Stage of Red Hepatization:

• Presence of erythrocytes (RBC) in the cellular interalveolar exudate.
• Neutrophil influx.
• Bacteria can be seen in specimens.

      3. Stage of Grey Hepatization:

• Erythrocyte extravasation (leakage) ceases.
• Neutrophil predominant.
• Abundant fibrin deposition.
• Disappearance of bacteria.

      4. Stage of Resolution:

• Macrophages reappear.
• Debris cleared.
• Inflammatory response cleared.

Clinical Features:

1. Fever
2. Rigors
3. Shivering
4. Delirium
5. Headache
6. Cough with sputum 
7. Rust colored sputum in patients with S.pneumoniae
8. Pleuritic chest pain
9. Respiratory and pulse rate raised.
10. Lower Blood pressure

Classification:

• Pneumonia was typically classified as:

1. Community-Acquired Pneumonia (CAP)
2. Hospital-Acquired Pneumonia (HAP)
3. Ventilator-Associated Pneumonia (VAP)

• Over the past few decades, however some persons presenting as outpatients with onset of pneumonia have been found to be infected with Multi0drug resistant pathogens previously associated with HAP; thus, development of the term Healthcare-Associated Pneumonia (HCAP).

• Classification on the Basis of Anatomy:

1. Lobar Pneumonia
2. Interstitial Pneumonia
3. Broncho Pneumonia

• Classification On the Basis of Etiology/Causes:

1. Primary Pneumonia
2. Secondary Pneumonia (including Aspiration pneumonia)
3. Suppurative Pneumonia (Necrotizing Pneumonia)

• Classification on the Basis of Mode of Acquiring Pneumonia:

1. CAP
2. HAP/ VAP
3. HCAP
4. Pneumonia in Immuno-compromised host

*Information Notes*

*Lobar Pneumonia: is a radiological and pathological term (involves lobe of the lung); referring to homogenous consolidation of one or more lung lobes with associated pleural inflammation.

Bronchopneumonia refers to more patchy alveolar consolidation associated with bronchial or bronchiolar inflammation often affecting both lower limbs (affects lungs along with bronchi).

Organisms responsible for Primary Pneumonia include Bacteria ( S.pneumoniae. H.influenza, Staphylococcus aureus, Pseudomonas aeruginosa) and Viruses (Adenovirus, Influenza virus, coronavirus, SARS associated coronavirus, Measles, Herpes Simples virus) *

Severity Assessment:

CURB-65

• Confusion
• Urea >7mmol/L
• Respiratory rate > 30/min
• Blood Pressure (systolic <90mmHg and Diastolic <60mmHg
• Age > 65years

Score 1 point for each feature!