Lecture 5 - Pneumonia and ARDS Flashcards
Describe the structure of the lung
Trachea
Bronchi
Bronchioles
Alveoli
Describe the defences in the lung
• Cilia covered with mucous beating mucous upwards • Alveolar macrophages • Neutrophils • Complement • Draining lymph nodes • IgA
Describe the presence of microorganisms in the respiratory tract
Lower lung: normally sterile
Where do infections most commonly occur in the respiratory tract?
What about the more dangerous lung infections?
Normally: bronchioles (bronchitis)
Serious: alveoli
Why is infection of the alveoli so dangerous?
Threatens oxygen exchange between air and blood
Which cells produce mucous?
Where are they?
Goblet cells
Interspersed in the epithelium of the respiratory tract
What are the cell types in the alveoli?
Type I pneumocytes
Type II alveolar cells
Alveolar macrophages
White blood cells (in interstitium)
What are Type I pneumocytes?
Elongated cell that forms the structure of the alveoli and the exchange epithelium
What are Type II alveolar cells?
Normally: Produce surfactant
Under pathological conditions: divide into new type I cells as a replacement
Where is surfactant found?
It is the physical lining of the type I alveolar cells
What is the role of alveolar macrophages?
Low numbers normally
Increase in the inflammatory response
What are the outcomes of pneumonia?
Recovery
Chronic inflammation
Death
What is pneumonia?
Acute inflammation of the alveoli and bronchioles
What are the general causes of pneumonia?
- Infectious
• Bacterial
• Viral
• Fungal - Non infectious
• Chemical pneumonia (ARDS)
• Aspiration pneumonia
What is chemical pneumonia normally called?
ARDS
Acute respiratory distress syndrome
What is inhalation / aspiration pneumonia?
Gastric, acidic contents of stomach breathed into the lung
Which people are most susceptible to pneumonia?
- Immunocompromised people
* The elderly
Describe how defences are compromised, leading to pneumonia
- Cilia immobilised due to smoking, loss of consciousness in acute alcohol consumption etc.
- loss of cough reflex
Which people commonly die from pneumonia?
People with other primary diseases, such as: • chronic alcoholism • AIDS • transplant immunosuppression • cystic fibrosis • cancer • burns • diabetes
Which are some infectious agents that cause pneumonia?
- S. pneumoniae
- Staphylococcus aureus
- H. influenza
- P. aeruginosa
- Candida
Why is pneumonia important?
N° 1 killer of children worldwide
What are the different types of pneumonia, in terms of acquisition?
Community-acquired
• acute
• atypical
Nosocomial pneumonia
Compare symptoms of community-acquired acute and atypical pneumonia.
Acute: large volume of inflammatory exudate
Atypical: smaller amounts of exudate
What are the causes of nosocomial pneumonia?
Aquired in a health care setting, due to
• underlying chronic disease
• invasive procedures
• immunosuppresion
Which type of pneumonia is ‘necrotising’?
Aspiration pneumonia
How does pneumonia present?
- Lobar
• large areas of the lung affected - Focal
• small areas
How long does acute pneumonia last?
Around a week
Why does acute inflammation occur in acute pneumonia?
To dilute and destroy agent of injury
What are the main differences between acute and chronic inflammation?
Chronic: • longer lasting • more variable and complex • necrosis • fibrosis (vicious cycle)
What are the components of acute inflammation in pneumonia?
- neutrophil infiltration
- monocytes
- complement
- macrophages
Which cells are producing chemokines in acute inflammation?
What is the result of this?
Neutrophils
Recruitment of many other inflammatory cells
Which cells immediately increase in number during inflammation?
- neutrophils
* macrophages
What changes occur to the vasculature in acute inflammation?
- Increased permeability
* Vasodilation
What is the result of increased vascular permeability?
Tissue oedema
Compare focal and lobar pneumonia
Lobar: whole lobe of lung is affected uniformly
Focal: small areas affected
Affected = fluid filled
What is the name for pus build up in pneumonia?
Supparative response
Compare the appearance of the different types of pneumonia on a chest X-Ray
- lobar
* bronchopneumonia
Describe the time scale of acute pneumonia
1-2 days: lung heavy (blood, oedema)
2-4 days: Red hepatisation
4-8 days: Grey hepatisation
8 days onwards: Resolution
Compare and contrast red and grey hepatisation
Red:
• lung red, due to erythrocytes
• lung heavy
• full of liquid & fibrin
Grey: • lung grey-white • lung solid & heavy • more fibrin • more neutrophils • blood has disappeared
What is the function of regions of oedema in the lung?
Non-functional
What is stasis and congestion in the lung?
When does this happen?
Lung full of fluid, blood and proteins
Can not function normally
Happens around 2-4 days
What happens in resolution of acute pneumonia?
Fluid reabsorbed back into alveolar epithelium and cells migrate away
What are pores of Kohn?
Openings connecting alveoli together
What are complications of lobar pneumonia?
- necrosis
- pleurisy
- bactaraemic dissemination
What is pleurisy?
Infection and inflammation of pleural cavity
Which organs are affected in bactaraemic dissemination?
Endocarditis
Pericarditis
Meningitis
Nephritis
What are the symptoms of lobar pneumonia?
- malaise
- fever
- child
- productive cough
- ARDS
What are the symptoms of ARDS?
- Increased work of breathing
- Severe hyperaemia
- Decreased CO2 excretion
What is the major treatment of pneumonia?
Antibiotics
* must be appropriate for infectious agent *
Compare histology of acute and chronic inflammation
Chronic:
• Cuboid, thickened of type I alveolar cells
• Macrophages and lymphocytes
Acute:
• Blood
• Neutrophils
What is the effect of the thick, cuboid type I alveolar cells in chronic inflammation?
Very poor oxygen exchange across epithelium
What is the difference between pneumonia and ARDS?
ARDS:
• modern definition of acute lung injury
• high mortality rate
• severe damage to alveoli themselves, as well as surfactant
• a result of a myriad of diseases, as well as direct lung injury
• acute onset of respiratory failure
• bilateral infiltrate on Chest X ray
What is the mortality rate of ARDS?
Around 40% mortality rate
What are some causes of ARDS?
- Gastric aspiration
- Near drowning
- Oxygen toxicity from Scuba diving
- Gas inhalation
What are some differences of the inflammatory response in ARDS, compared to pneumonia?
In ARDS:
• NECROSIS
• Lots of cellular debris due to necrosis of type I alveolar cells
• Complete denudation of the alveoli (no living cells)
• Loss of surfactant
• Formation of hyaline membrane
What are the phases of ARDS?
- Exudative
2. Organising
Describe the exudative phase of ARDS
- very rapid oedema
- degenerative changes to type I alveolar cells, then sloughing
- formation of hyaline membrane
- inflammatory infiltrate
- (+/- thrombi)
Describe formation of hyaline membrane
This occurs in ARDS
• Lots of proteins laid down
• Starts after about 2 days
Describe the organising phase of ARDS
Recovery attempt of alveoli
Often leads to fibrosis
Describe resolution of ARDS
Resorption of exudate
• Na/K ATPase, aquaporins resetting the osmotic balance
What are the possible outcomes of ARDS?
- Death
- Resolution
- End stage fibrosis
What is end stage fibrosis?
‘Honeycomb lung’
• tissue
What are some treatments of ARDS?
- Mechanical ventilation (most effective)
- Inhalation of NO
- Anti-inflammatory drugs
Future:
• mesenchymal stem cells
What is the effect of NO?
Vasodilation, increased gas exchange
What is one of the most important anti-inflammatory drugs?
Glucocorticoids
Describe the effect of mesenchymal stem cells
• Increased IL-10 (suppressive cytokine) • decreased inflammatory cytokines Leads to: • structural recovery • reduced pulmonary oedema
Rapid inflammatory response in the lungs?
ARDS
not pneumonia
Which cells produce surfactant?
Type II alveolar cells
Which pathogens often lead to atypical pneumonia?
- Mycoplasms
* Influenza virus
