Lower Respiratory Tract Infections Flashcards
What constitutes the lower respiratory tract?
Everything in the respiratory tract below the larynx
Define tracheitis
Rare, LRTI affecting the trachea.
Can be viral or bacterial, often overlaps with laryngitis
Define bronchitis
LRTI affecting the bronchi; may be acute or chronic
Define bronchiolitis
LRTI affecting the bronchioles; most common in children <2 years old.
Viral: usually RSV.
Define pneumonia
LRTI affecting the alveoli; can be lobar or multifocal.
Define pleural infection
Infected pleural effusion → Empyema
How are lung abscesses formed?
Severe airway damage or haematogenous spread (e.g. infection spread from infected heart valve into the lungs → abscess)
List the causative classifications of LRTI
Define each term
- Infective exacerbation of COPD
- Community acquired pneumonia (possibly due to common and sensitive organisms)
- Hospital acquired pneumonia (possibly due to rare and resistant organisms)
- Atypical pneumonia (uncommon organisms)
- Secondary pneumonia (bacterial pneumonia following viral LRTI)
- Aspiration pneumonia
- Opportunistic LRTI (often due to immunodeficiency or immunosuppression)
Describe the aetiology of bronchitis
Acute = mostly viral
Chronic (e.g. COPD) = mostly bacterial
Common organisms:
- Rhinovirus
- Influenza
- Streptococcus pneumoniae
- Haemophilius influenzae (associated with underlying airway damage)
More common in patients who have underlying airway damage
Describe the aetiology of pneumonia
Typical microbes:
- Influenza
- Streptococcus pneumoniae
- Staphylococcus aureus (can occur following influenza)
More common in patients who are immunocompromised
Name some host risk factors for LRTI
Extremes of age
Stress and starvation
Immunocompromised host
Compromised barriers to infection:
- Smoking (reduced ciliary action, bronchitis)
- Viral LRTIs damage respiratory tissues leading to bacterial LRTIs
- Depletion of antimicrobial organisms secondary to antibiotic treatment
- Obstructions (e.g. tumours)
- Iatrogenic (broncoscopy, tracheostomy)
Describe the pathogenesis of LRTI
Access: resp tract is open to the environment
Adherence: pathogenic organisms have receptors for respiratory tissues
Invasion: damaged respiratory tissues help invasion
Multiplication: good nutritional environment for micro-organisms
Evasion: immune cells are present, however damaged tissues help with evasion
Resistance: drug resistant micro-organisms
Damage: LRTIs cause bronchitis, pneumonia and septicaemia
Transmission: easily transmitted by respiratory secretions
Name the features of bronchitis (pathology, symptoms, signs, investigations)
Is sepsis from bronchitis common or uncommon?
Pathology = infection & inflammation of airways
Symptoms = dyspnoea, cough, sputum (usually), wheeze
Signs = fever (usually), tachypnoea, crackles, wheeze
Investigations = hypoxia (possibly), normal CXR (usually)
Sepsis = uncommon
Name the features of pneumonia (pathology, symptoms, signs, investigations)
Is sepsis from pneumonia common or uncommon?
Pathology = infection & inflammation of alveoli
Symptoms = dyspnoea, cough (usually), sputum (usually), pleurisy
Signs = fever, tachypnoea, crackles, ↓ breath sounds or bronchial breath sounds (tissue is consolidated- louder breathing)
Investigations = hypoxia (possibly), abnormal CXR (consolidation)
Sepsis = common
Name some investigations for LRTIs
- Peak flow (?obstruction)
- Pulse oximetry
- FBC: ?leukocytosis
- U&Es: ?sepsis ?AKI
- CRP: raised in bacterial infection
- Lactate: increased in severe sepsis
- ABGs: hypoxia+/- hypercapnia
- CXR: shadowing/pleural effusion/empyema
- Nose and throat swabs: viral
- Sputum culture: bacterial infections
What does this x-ray show?
Right lower lobe consolidation (R lower lobe pneumonia)
What does this x-ray show?
What is the commonest cause of this type of x-ray appearance in HIV patients?
Pneumonitis (diffuse pneumonia)
Most often caused by pneumocystis in HIV patients
