Pathology of Respiratory Tract Infection Flashcards
RTIs can be primary, facultative or opportunistic. What is meant by these terms?
Primary: patient well but has interacted with the right organism to make them unwell
Facultative: relatively healthy patient but with a risk factor to RTI
Opportunistic: only really infects immunocompromised indivdiuals
Give e.g.s of upper RTIs
Coryza (common cold) Sore throat syndromes Acute laryngotracheobronchitis (croup) Laryngitis Sinusitis Acute epiglottitis
What causes acute epiglottitis?
Hib
Who does epiglottitis primarily affect?
Was seen as a disease of childhood, but now more common in adults due to immunisation
What are features of acute epiglottitis?
Rapid onset
High temperature, generally unwell
Stridor
Drooling
What sign can be seen on CXR in acute epiglottitis?
A lateral view may show swelling of epiglottis - thumb sign
Give e.g.s of LRTIs
Bronchitis
Bronchiolitis
Pneumonia
What defense mechanisms does the respiratory tract have against infections?
Mucociliary escalator + macrophages
Humoural and cellular immunity - antibac secretions
URT acts as a filter (e.g. nose filters out large particles, complex space + large SA –> tuberulent flow = more particles trapped)
Nasal hair
What is the mucociliary escalator?
Macrophages can’t always digest debris so they move to the escalator to be cleared
What happens when the mucociliary escalator fails?
Secretions/FBs are retained in the lung –> secondary bacterial infection
When does the mucociliary escalator fail?
Tends to happen in a viral LRTI (viruses destroy the resp epithelial layer = deficient cilia)
What are 5 classifications of pneumonia based on aetiology?
Community acquired Hospital acquired/nosocomial (more aggressive + more likely to be resistant to antibiotics) Atypical Aspiration Recurrent
What causes an aspiration pneumonia?
Aspiration of gastric contents in the context of abnormal vomiting
What does aspiration pneumonia often result from?
Incompetent swallowing mechanism, e.g. in neurological disease/injury, like stroke or intoxication
What are iatrogenic causes of aspiration penumonia?
Intubation
What are RFs for developing an aspiration pneumonia?
Poor dental hygiene Swallowing difficulties Prolonged hospitalisation/surgical procedures Impaired consciousness Impaired mucociliary clearance
What bacteria most commonly are implicated in an aspiration pneumonia?
Streptococcus pneumoniae
Staphylococcus aureus
Haemophilus influenzae
Pseudomonas aeruginosa
What are different patterns of pneumonia?
Bronchopneumonia (diffuse)
Segmental
Lobar
Hypostatic (accumulation of secretions/fluid in lower bits of lungs –> increased risk of infection) - usually due to cardiac failure
Where does bronchial pneumonia affect?
Patches throughout both lungs (bronchioles + adjacent areas of lung)
What things commonly cause a bronchopneumonia?
AECOPD
Bacterial pneumonia etc.
If the patches of affected lung in a bronchopneumonia join up what is this called?
Confluent bronchopneumonia
What will you see on CXR in bronchopneumonia?
Bilateral basal patchy opacifications
Where does a lobar pneumonia affect?
Primarily the alveoli of a lobe of lung
Can extend out to reach pleura
Which of bronchopneumonia and lobar pneumonia are more aggressive?
Lobar
What are complications of pneumonia?
Empyema Pleural effusion Organisation - fibroses e.g. COP (cryptogenic organising pneumonia) or BOOP (bronchiolitis obliterans organising pneumonia) Lung abscess Bronchiectasis Death
What does an organising pneumonia often resemble?
A lung cancer
How can a lung abscess form after a pneumonia?
Acute inflammatory process –> destruction of lung tissue
Pus gathers in this space
What organisms are commonly impacted in a lung abscess?
Staph aurues
Pneumococci
Klebsiella
What is bronchiectasis?
Permanent dilatation of airways secondary to chronic infection/inflammation
What are causes of bronchiectasis?
Post-infective - TB, measles, pertussis, pneumonia
CF
Bronchial obstruction, e.g. lung cancer/FB
Immune deficiency: selective IgA hypogammaglobulinaemia
Allergic bronchopulmonary aspergillosis
Ciliary dyskinetic syndromes, e.g. Kartagener’s syndrome, Young syndrome
Yellow nail syndrome
What is the pathophysiology of bronchiectasis?
Damaged drug contracts and pulls airways open leading to bronchiectasis which disrupts the mucociliary escalator + increases risk of infection
What are clinical features of bronchiectasis?
Cough Abundant, purulent, foul sputum Haemoptysis (haemorrhaging from dilated airways) Crackles Clubbing
How is bronchiectasis treated?
Assess for treatable causes then:
Physical training, e.g. inspiratory muscle training
Postural drainage
Antibiotics for exacerbations, long term antibiotics in severe cases
Bronchodilators
Immunisations
Surgery e.g. for localised disease
What are the most common organisms isolated from patients with bronchiectasis?
Haemophilus influenzae (most common)
Pseudomonas aeruginosa
Klebsiella spp.
Streptococcus pneumoniae
What may be reasons for recurrent lung infections?
Local bronchial obstruction, e.g. tumour/FB
Local pulmonary damage e.g. bronchiectasis
Generalised lung disease - COPD? CF?
Non-resp problems - immunocomp (HIV) Aspiration?
What is respiratory failure?
Gas exchange at the lungs is impaired so lung that hypoxaemia occurs (with or without an increase in CO2 levels)
What is type 1 respiratory failure?
Low oxygen and normal or low CO2
What is type 2 respiratory failure?
Low oxygen and high CO2
What is type 1 respiratory failure generally due to?
Damage of the lungs –> impaired gas diffusion (remaining normal lung still able to excrete CO2)
What is type 2 respiratory failure generally due to?
Ventilatory failure - it occurs when alveolar ventilation is insufficient to excrete CO2, may be due to reduced ventilatory effort or inability to overcome increased resistance to ventilation
Which of a V/Q mismatch and a shunt responds best to increases in FiO2?
V/Q mismatch
What is a shunt?
Passing of blood from the R to the L side of the heart without contacting ventilated alveoli
What is cor pulmonale?
When a disorder of the lungs causes right sided heart dysfunction (–> R heart failure)
What is the pathophysiology of cor pulmonale?
Lung disorder –> harder to oxygenate blood –> hypoxia –> hypoxic pulmonary vasoconstriction (when a pulmonary arteriole is next to a poorly ventilated aveoli it constricts to shunt blood) –> increase in resistance –> pulmonary hypertension –> hard for right ventricle to push against this pressure (remember RV is thin and is made to push against low pulmonary resistance)
How can you tell the difference between an acute and a chronic lung disorder leading to increased pressure in the right ventricle?
In acute disorder - there is a rapid increase in pressure and so the RV balloons
In chronic disorder - prolonged high pressure –> hypertrophy of RV
Why is RV hypertrophy in chronic lung disease a problem?
Less space for blood to fill RV –> diastolic heart failure
Increase in wall size means it requires more oxygen to pump
Increased bulk puts pressure on coronary arteries so even less blood delivered RV
All this leads to RV ischaemia –> weaker contraction + systolic failure
What is the main thing that causes cor pulmonale?
Pulmonary hypertension
What 3 things can cause pulmonary hypertension and lead to cor pulmonale?
Damage to the lung tissue, e.g. COPD
Damage to the pulmonary vessels, e.g. recurrent blood clots
Disease of spine/ribcage, e.g. kyphoscolosis (lungs cannot expand properly)
What are the symptoms of cor pulmonale?
Due to backup of blood in venous system - Severe SOB Fatigue Fainting JVP elevated Hepatomegaly Oedema
How is cor pulmonale diagnosed?
ECG shoes evidence of increased pressure in pulmonary vessels and ventricle
What is the gold standard technique used to assess pulmonary pressures in cor pulmonale?
Right heart catheterisation
How is cor pulmonale treated?
Treat underlying lung disease
Supplementary oxygen
