Flashcards in 11. Pathology of Respiratory Tract Infection Deck (104):
Are lung infections multifactorial or dependent on a single factor?
What is a primary pathogen?
-Organism that causes the disease when it gains entrance to the host's body and stresses victim's immune system.
-"the bad ones"
-cause an infection in any human they encounter
What is a facultative pathogen?
- seen the most in patients in clinical practice
- can reproduce either inside or outside host/ cells
-"need a bit of help"
-predisposing pulmonary pathology can lead to establishment of facultative organisms
What is an opportunistic pathogen?
- takes advantage of a host with a weakened immune system or disrupted gut flora for example
-least pathogenic organism
What are the two most important factors that influence the capacity to resist an infection?
1. state of host defence mechanism (patient's immunity)
2. age of patient
What level of sterility are upper resp. tract and lower resp. tract?
What are 6 very common URT infections?
1. coryza (common cold)
2. sore throat syndrome
3. acute laryngotracheobronchitis (croup)
6. acute epiglottis
What is the main cellular pathology of the URT infections?
inflammation (acute or chronic)
What is epiglottis?
-cartilaginous flap which prevents food and liquid from falling into airways
-stays open to allow easy movement of air but closes during swallowing for protection
Describe features of acute epiglottitis.
- inflammation of epiglottis causing swelling and blockage of airways
-affects young children often
-can be severe and life threatening
What 2 types of bacteria cause acute epiglottitis?
-Group A beta-haemolytic streptococci
-haemophilus influenze (type b- Hib)
What are common LRT infections?
4. consequences (of another infection)
5. possible complications (of other infections)
What is the MOST important respiratory tract defence mechanism?
macrophage-mucocilliary escalator system
What 3 other respiratory tract defence mechanisms exist?
1. General immune system (humoral and cell mediated immunity)
2. Respiratory tract secretions (antibacterial components of secretions which contribute to mucociliary system)
3. Upper respiratory tract acts as a "filter" (nose)
Failure in the 3 respiratory tract defence mechanisms can lead to what?
increasing risk for respiratory tract infections as viruses and bacteria are not removed
How does the URT act as a "filter"?
-Nose (component of URT) acts as a filter as when air flows into the nose, the flow is turbulent
-Surface of resp. tract is lined with mucus, cilia and moisture
-Particles are deposited in the resp.tract (e.g. nasal hair)
What features of the air are important in the mucociliary escalator system? (2)
humidity and temperature
What are the 3 components of macrophage-mucociliary escalator system?
1. alveolar macrophages
2. mucociliary escalator
3. cough reflex
Describe the role of cilia in particle clearance of the lungs.
-Cilia beat the mucus in coordinated fashion as escalator moves only up and out of the lung (flowing carpet of mucus)
- Mucus sweeps any foreign particles away from the resp. tract
Describe the role of alveolar macrophages in in particle clearance of the lungs.
-found in alveoli region
-phagocytose foreign particles which enter lower resp. tract by clearing up
- macrophages deposit particles onto the moving mucociliary escalator which removes it via the escalator moving upwards towards URT
- macrophages enter interstitial pathway via lymph to the lymph nodes to be used again
Where are many foreign particles found in the LRT?
deposition on the terminal bronchioles/proximal alveoli
Where is muco-ciliary escalator found?
on the conducting airways towards URT (build up at the back of throat that is often swallow is due to particles building up that have been removed from the lungs)
What clearance mechanism is used to keep the LRT sterile?
What happens if defence mechanism fail?
secretions with bacteria and viruses are retained in the lung leading to infection
What happens if a respiratory virus is inhaled?
- virus infects cells to survive and kills the cell which it uses for replication
- causes damage to respiratory epithelium
-this leads to abnormal cells with no cilia and sometimes the whole epithelium is stripped
When do bacterial infections often occur in relation to viral infections?
Often AFTER viral infections because viruses cause the damage first which makes person more susceptible to bacteria
What are the 3 classifications of pneumonia when approaching the disease?
1. anatomical (radiology, how it looks on imaging)
2. Aetiological (cause/circumstance, how the disease occured, allows doctors to predict organism)
3. Microbiological ( appropriate ultimately for treatment, material from patient obtained and sent to microbiology for testing)
What are the 5 aetiological classifications of pneumonia?
1. community acquired pneumonia
2. hospital acquired (nosocomial) pneumonia
3. pneumonia in immunocompromised
4. atypical pneumonia
5. aspiration pneumonia
5. recurrent pneumonia
What is meant by community acquired pneumonia?
-Person had little contact with healthcare system
-Most common type
What is meant by hospital acquired pneumonia (nosocomial)?
- contracted in healthcare environment
- more antibiotic organisms exist
What is meant by atypical pneumonia?
-unusual agents (bacteria) present
What is meant by pneumonia in immunocompromised?
high mortality rates for patients with weak immune systems
What is meant by aspiration pneumonia?
-Entrance of foreign material into bronchial tree; usually oral or gastric contents such as saliva, food, nasal secretions or vomit causing infection
- acidity of the aspirate can lead to chemical pneumonitis
What is meant by recurring pneumonia?
-patient comes back episode after episode especially in the same place in the lung
-indicates serious infection that needs attention
What is the most common bacterium to cause pneumonia outside hospitals?
Streptococcus pneumoniae (causes half of all pneumonias)
What are 2 bacteria can cause pneumonia?
1. haemophilus influenzae; common in patients with pre-existing lung disease such as chronic bronchitis
2. staphylococcus aureus; more common in children and intravenous drug users
Can pneumonia be also caused by viruses?
Yes, most commonly influenza A virus
What are 3 types of patterns of pneumonia?
What is bronchopneumonia?
More widespread infection in bronchi and bronchioles (widespread lung inflammation)
What is lobar/segmental pneumonia?
-refers to infection of one lobe of the lung
-lobar and segmental almost the same thing
-segmental refers to segment of lobe affected
What is hypostatic pneumonia?
- has accumulation of fluid in the lung as they settle in one part of the lung increasing chance of infection
- common in elderly who remain in one position for long periods
- failure to drain bronchial secretions or pulmonary oedema from chronic bronchitis or heart failure patients
- fluid builds up in R.ventricle causing infection as it sits in lower part of lung
-fluid lies at the bottom ready for infection and doesn't move
What is aspiration pneumonia?
-develops due to entrance of foreign materials into bronchial tree
-usually gastric or oral contents; saliva, food, nasal secretions, vomit
-moves to the LRT causing infection
What is obstructive, retention, endogenous lipid pneumonia?
-develops when lipids enter the bronchial tree
-can be exogenous if oil droplets inhaled
-can be endogenous if body itself is causing it, when lipid-laden macrophages and giant cells fill the lumen of disconnected airspace
What does lobar pneumonia look like on an x ray?
- secretions wash microorganisms around lungs and fill anatomical segment until pleura is reached
-lobes look solid (loss of function)
Why might pneumonia not resolve?
-fibrous tissue can form, which is a normal reaction for inflammatory process that will not resolve on its own
-happens on the inside on the lung
What are the main complications of pneumonia? (7)
-inflammation of lung pleura
2. Pleural Effusion (fluid)
- excess fluid accumulating in pleural cavity
-pockets of pus collected in body cavities
-COP (cryptogenic organising pneumonia) -BOOP (bronchiolitis obliterans organising pneumonia; alternative name
5. lung abscess
-cavity filled with necrotic debris/ fluid caused by infection
-airways become abnormal widened; long term condition leading to build up of mucus and more susceptible to infection
7. fatal outcome (death)
What is an example of organising pneumonia that has 2 names?
1. COP; cryptogenic organising pneumonia
2. BOOP; bronchiolitis obliterans organising pneumonia
What happens in a lung abscess?
-Formation of cavities filled with necrotic tissue and fluid caused by microbial infection
Leads to destruction of lung tissue
-leads to gathering of pus
What can cause a lung abscess?
- obstructed bronchus (tumour)
-following a lung infection (suppressed immunity)
What 3 organisms commonly cause lung abscesses?
- staph aureus
When are are lung abscesses metastatic?
in pyaemia (pus spreads through blood)
Which degree of infection is a necrotic lung?
What is the most common type of pneumonia?
staphylococcal pneumonia (biggest killer during influenza pandemics)
What is bronchiectasis?
Pathological and abnormal widening of bronchi ( widening of airway vessels)
What are 4 most common causes of bronchiectasis?
1. severe infective episodes (e.g. childhood infections)
2. recurrent infections/immunodeficiency (many causes e.g. tumours)
3. proximal bronchial obstruction
4. lung parenchymal destruction (part involved in gas transfer) due to connective tissue disease or cilia abnormalities (muco-ciliary escalator failure)
What common childhood infective episodes could contribute to bronchiectasis? (4)
- whooping cough
What percentage of bronchiectasis patients have the condition start in early childhood?
What are signs of bronchiectasis?
2. abundant purulent foul sputum
4. signs of chronic infection
5. coarse crackles
What 2 tests should be done for patients with bronchiectasis?
2. thin section CT (dilated bronchi appear too close to the pleura)
What are the common treatment options for bronchiectasis?
1. postural drainage
What causes should be investigated if there is a recurrent local bronchial obstruction? (2)
What cause should be investigated if there is a recurrent local pulmonary damage? (1)
What cause should be investigated if there is a recurrent generalised lung disease? (3)
What cause should be investigated if there is a recurrent non-respiratory disease?
-HIV or other?
What is the most common place for aspiration pneumonia?
right bronchus (obstruction most likely to happen there as it's more vertical than the left)
What are common causes of aspiration pneumonia? (5)
2. oesophageal lesion
3. obstetric anaesthesis
4. neuromuscular disorders
What opportunistic organisms?
-Organisms not normally capable of producing disease in patients with intact lung defences and only attack patients who are immunocompromised (weak).
- they take their opportunity to arrack
-increased chance of ordinary infections
What are 4 common opportunistic pathogens?
1. low grade bacterial pathogens
2. CMV: cytomegalovirus
3. pneumocystis jirovecii (yeast-like fungus)
4. other fungi and yeast
What 2 types of bulk flow are there?
Where does laminar airflow occur?
Where does turbulent air flow occur?
What occurs BEYOND the terminal bronchiole?
diffusion (gas exchange)
Where is the blood-air barrier found?
in the alveolar walls
What does the bulk flow highly depend on?
the pressure difference
Is Hb 100% saturation of O2 possible?
What is the usual Hb saturation?
98% saturated for O2 of only 21% (in the air)
Why does CO2 rapidly equilibrate between blood and air?
because CO2 is very soluble
What are the normal PaO2 parimeters?
10.5-13.5 kPa (usually 13.3)
What are the normal PaCO2 parimeters?
4.8-6 kPa (usually 5.3)
What can respiratory failure be defined by?
levels of oxygen and carbon dioxide
When does Type 1 respiratory failure occur?
When PaO2<8kPa (PaCo2 is normal or low)
When does Type 2 respiratory failure occur?
When PaCO2 >6.5kPa (PaO2 is usually low )
Which type of respiratory failure affects the whole respiratory system?
Type 2; as both O2 and CO2 affected, CO2 accumulation that cannot be eliminated by the body
What 4 abnormal states are associated with hypoxemia? (low oxygen in blood)
1. ventilation/perfusion imbalance (V/Q)
2. diffusion impairment
3. alveolar hypoventilation
What happens to pulmonary vessels during hypoxia? (perfusion>ventilation when alveolar oxygen tension falls)
-pulmonary arteriolar vasoconstriction (all vessels constrict if there is arterial hypoxaemia)
-it doesn't send blood to alveoli short of oxygen (it redirects blood to better oxygenated areas; SHUNT)
In what disease does ventilation/perfusion abnormality (mismatch) occur?
Bronchitis (bronchopneumonia) although some ventilation of abnormal alveoli still occurs (just not enough)
When does shunt happen in disease?
-in severe bronchopneumonia
-lobar pattern with large areas of consolidation
- occurs when there is ZERO and NO ventilation
What is the normal V/Q ratio?
~80% (normal breath= 4L and cardaic output= 5L so 4/5)
Is low V/Q the commonest cause of hypoxaemia encountered clinically?
Yes; low V/Q in some alveoli arises due to local alveolar hypoventilation due to focal disease
Doe hypoxaemia due to low V/Q respond well to even small increase in FlO2?(filtered O2)
When does pathological shunt occur? In what 3 circumstances? (3)
1. arteriovenous (AV) malformations
2. congenital heart disease
3. PULMONARY DISEASE
When does shunt occur?
Blood passes from right to left side of heart WITHOUT contacting ventilated alveoli as blood is redirected to better ventilated areas
Do large shunts respond well to increases in Fl O2?
No, large shunts respond poorly (blood leaving normal lung is already 98% saturated)
Why does ventilation/perfusion abnormality (mismatch) arise in COPD? (hypoxaemia)
due to airway obstruction
Why does alveolar hypoventilation arise in COPD? (hypoxaemia)
due to reduced respiratory rate
Why does diffusion impairment arise in COPD? (hypoxaemia)
due to loss of alveolar surface area
When does shunt arise in COPD? (hypoxaemia)
only during acute exacerbation (worsening of symptoms)
What happens during alveolar hypoventilation? (in terms of O2 and CO2)
- insufficient amount of air moved in and out of lungs
- increases PACO2 and thus increases PaCO2
- this leads to decrease in PAO2 and thus decrease in PaO2
What is falling in PaO2 corrected by?
FlO2 (fraction of inspired air which is oxygen)
What is hypoxic Cor Pulmonale?
Impairment in right ventricular function as a result of a respiratory disease leading to increased resistance to blood flow in pulmonary circulation leading to pulmonary hypertension
Why is pulmonary hypertension caused by hypoxic cor pulmonale?
- pulmonary vasoconstriction occurs
- leads to pulmonary arterioles causing muscle hypertrophy and intimal fibrosis (r. ventricle becomes thicker)
-loss of capillary bed occurs
- secondary polycythaemia (high conc. of RBCs)
What surgical procedure is required for hypoxic cor pulmonale? (which causes pulmonary hypertension)
bronchopulmonary arterial anastamoses
What is chronic (hypoxic) cor pulmonale?
-hypertrophy of the r. ventricle resulting from disease affecting the function and/or structure of the lung