Inflammatory process of the lung parenchyma

The parenchyma is the portion of the lungs where gas transfer occurs and
includes: the respiratory bronchioles, alveolar ducts, and alveoli.
Children and older adults are at increased risk for developing pneumonia, as well
as the immunocompromised.

Patho
Once the pathogen enters the airways (either by: aspirating oropharyngeal
secretions, lack of usual movement of respiratory secretions, inhaling particles in
the air, or introduction via devices like suction catheters or endotracheal tubes)
adjacent spread occurs from the pathogen to other areas of the lung. The key
defense mechanism for pathogens within the lungs are alveolar macrophages.
Activation of neutrophils, lymphocytes, and platelets leads to an inflammatory
response at the site. Exudate and cell debris from the inflammatory response
accumulate in the alveoli and bronchioles, impairing gas exchange and causing
dyspnea and hypoxemia.

Causes
 Usually infectious agents
 Immune response
 inflammation can occur due to injury or trauma (inhalation of chemicals).

Categorizations
 Individual risks characteristics
 Anatomic lung distribution involvement
 Location of acquisition
Types based on area:
 Anatomically, there are 3 places in which pneumonia occurs:
o lobal pneumonia: often the result of Streptoccocus pneumoniae and
other bacteria. It is the most acute in onset and tends to have the
most severe symptoms.
o Bronchopneumonia: often the result of a polymicrobial infection.
o interstitial pneumonia: caused by viruses or mycoplasma.
o Broncho & interstitial: have variable, insidious onsets that can have
milder symptoms in comparison to lobar pneumonia
o This is often how pneumonia is reported on x-ray reports.
Types

Community-acquired pneumonia
 caused most commonly by gram-positive bacteria Streptococcus
pneumoniae.
 Other agents include Haemophilus influenzae, and Staphylococcus aureus.
 Some gram-negative agents can also cause CAP.
 Cases of CAP that are caused by bacterial are termed bacterial pneumonias,
and have more severe symptoms, as described in the above slide.
 X-ray usually shows infiltrates or consolidation and antibiotics are usually
required.

Atypical pneumonia
 refers to pneumonia that occurs with atypical organisms, like Chlamydia
pneumoniae, and Legionella species pathogens.
 Mycoplasma pneumoniae is a common cause of “walking pneumonia” and
symptoms are generally mild.
 Legionnaire’s disease (caused by Legionella pneumophilia) occurs most
often in those who work or live in warm, moist environments like air-
conditioning system workers (because the bacteria thrive in these settings)
and so development of Legionnaire’s disease occurs as people inhale the
bacteria contained in water droplets.
 o Legionnaire’s disease also affects those who are
immunocompromised.

Hospital-acquired pneumonia
 defined as a pneumonia that occurs within 48 hours after admission to
hospital and includes ventilator-associated pneumonia.
 This develops 48 hours after intubation.
 They are thought to be polymicrobial due to the nosocomial nature of
these infections.

Aspiration pneumonia
 occurs when the gag reflex is impaired, or closure of the lower esophageal
sphincter is impaired
 Gastric contents or secretions enter the lungs and irritate the lung tissue,
leading to inflammatory response.

Viral pneumonia
 most commonly influenza, adenoviruses, paramyxoviruses like RSV and
coronavirus
 Viral tends to be slightly milder in nature compared to bacterial pneumonia
(see table on slide), but can cause significant respiratory distress & failure
(as seen in those with severe COVID infections or severe acute respiratory
distress syndrome [SARS])
 Understanding that SARS can occur due to viral pneumonia is most
important in combination with understanding the presentation symptoms
you might see in primary care, like cough, fever, chills, headache, anorexia,
dyspnea (not necessary to know the stages of SARS as this is very rarely
something you would see in primary care).

Fungal pneumonia
 most common in those who are severely immunocompromised (cancer,
AIDS) or with developing immune systems (children).
 Pneumocystis jiroveci is a specific type of pneumonia caused by a yeastlike
fungus.

Middle East respiratory syndrome

Diagnosis
 Chest X-ray (GOLD STANDARD)- determines consolidation, effusions,
infiltrates
 Clinical prediction scores
o determine if the patient should be admitted to hospital
o most commonly used is the CURB65 criteria
o For older adults especially
o Resps, bp, urea, age to evaluate risk
 Other testing: sputum culture, antigen testing (for Legionella) or COVID-19
may be performed. CBC, ABGs, and bronchoscopy

Treatment
 Management of respiratory distress
 Broad-spectrum antibiotics (if suspected a bacterial pneumonia based on
the history) may be initiated while awaiting a chest x-ray.
 Viral pneumonia is usually mild and heals without intervention, but can
lead to virulent bacterial pneumonia (due to opportunistic bacterial growth
within the inflammatory response
 Prevention is key – aimed at vaccination against viral agents and bacterial
agents like Streptococcus pneumoniae and Hib.