Asthma Flashcards
Define asthma
Chronic, obstructive intermittent inflammatory airway disease characterised by reversible airway obstruction, airway hyper-reactivity and bronchial inflammation
What is the aetiology of asthma
Multiple gene associations + environmental exposure
Gene: ADAM 33, atopy, family history, dipeptidyl peptidase 10
Environment: dust mites, pollen, pets, cigarette smoke, viral RTI
What are the risk factors for asthma
Atopic history
Family history of atopic disease e.g. asthma, eczema, allergic rhinitis, allergic conjunctivitis
Respiratory infections in infancy
Prenatal exposure to tobacco smoke
Premature birth and LBW
Obesity
GORD
Male sex for pre-pubertal asthma and female sex for persistence of asthma from childhood to adulthood
What % of the population are affected by asthma
10% children, 5% adults
Prevalence increasing
What is the pathogenesis of asthma
Wall inflammation, thickening, tight smooth muscle
Early phase (1h): exposure to inhaled allergens in pre-sensitised individual → cross-linking of IgE Abs on mast cells → histamine, prostaglandin D2, leukotriene, TNF-alpha release → smooth muscle contraction, mucous hypersecretion, oedema, obstruction
Late (after 6-12h): eosinophil, basophils and neutrophil recruitment
What are the symptoms of asthma
SOB/dyspnoea/breathlessness
Cough (worse in the night or morning)
Wheeze
Chest tightness
triggers: recent RTI, exercise, allergens/irritants, cold weather, emotion/laughter
What is Samter’s triad
three conditions which commonly cluster together: asthma, nasal polyps and aspirin sensitivity
What are the differentials for asthma
Viral induced wheeze
Bronchitis
Bronchiectasis
Ciliary dyskinesia
Cystic fibrosis
Bronchiolitis
Croup
Foreign body aspiration
GORD
Pertussis
What are the signs of asthma on examination
Obs: tachypnoea
Height and weight
General: assess consciousness
Cardio
Resp:
- Expiratory polyphonic wheeze (multiple pitches and tones heard over different areas of the lung when the person breathes out)
- Tachypnoea
- Use of accessory muscles
- Prolonged expiratory phase
- Hyperinflated
What investigations should be done for asthma
<5yo: clinical diagnosis
5-16: Spirometry + BDR ± FeNO
>16: FeNO → spirometry + BDR ± PFV ± BC ± specialist diagnosis
Bedside: peak expiratory flow rate (PEFR) + variability (PFV) >20%
Bloods:
Other:
- Spirometry: FEV1/FVC ratio <70%
- Bronchodilator reversibility: improvement in FEV1 of >12% / >200mL increase in volume after SABA
- FeNO testing: >35ppb (measure of airway inflammation)
- Bronchial challenge: PC20 ≤8mg/mL (with methacholine or histamine challenge)
What are the features of a moderate asthma exacerbation
PEF 50-75% best or predicted
No signs of severe asthma
What are the features of a severe asthma exacerbation (>12yo)
PEF 33-50% of best or predicted
RR >25
HR >110
Inability to complete sentences in one breath
Accessory muscle use
What are the features of a life-threatening asthma exacerbation (>12yo)
PEF <33%
Low sats
Normal CO2
Cyanosis or confusion
Hypotension
Exhaustion
Silent chest
Tachycardia
What are the features of a near-fatal asthma exacerbation (>12yo)
Raised PaCO2
Requires mechanical ventilation
What is the management for a mild acute asthma exacerbation
Burst therapy
- Salbutamol (SABA) via spacer, 10 puffs total, one every minute, 5 tidal breaths per puff
- Repeat 10-20 minutes later according to response
- Discharge if better within 1 hour
- TAME: Technique, Avoid triggers, Monitor PEF, Educate
- Quadruple inhaled ICS for up to 2 weeks
- Follow up within 2 days of discharge (GP)