Download Asthma - Medically fit for exams

Asthma – DR DEACPIMP
Definition
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Chronic immune response
Airway obstruction – bronchoconstriction
Airway hyperresponsiveness
Reversible with β-2 agonists
Risk Factors
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Other atopic disorders (eczema, allergic rhinitis, atopic dermatitis)
Family history
Hygiene hypothesis
Smoking/parental smoking
Differential diagnoses
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COPD
Bronchitis
Bronchiectasis
α-1 anti-trypsin deficiency
Epidemiology
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1/10 children
1/20 adults
Hygiene hypothesis – less common if rural, high pathogen exposure, natural birth, fewer
antibiotics
Aetiology
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Genetic
Environmental triggers
o Exercise
o Emotion
o Cold air
o Infection
o Allergens
Clinical features
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Dyspnoea
Expiratory wheeze
Diurnal variation – worse when wake up/wake up with cough
Triggered by environmental stimuli
Reversible with salbutamol (short-acting beta 2 agonists)
Reduced PEV (peak expiratory volume) – peak flow
Pathophysiology
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Chronic: increased IgE and CD4 Th2 cells in circulation
Allergen/stimulus is presented on antigen-presenting cells
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Activated CD4 cells and antibodies (IgE) activate mast cells
Mast cell degranulation causes release of mediators such as cytokines and histamine that
cause eosinophil recruitment and inflammation, and also smooth muscle
contraction/bronchoconstriction
Chronic inflammation leads to hypertrophy of smooth muscle
Fibrosis/remodelling
Hyperplasia of goblet cells (secrete mucus)
Damaged epithelia (allows future allergens easy access)
Investigations
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Peak flow – PERF or PEV is below 80% of expected (CHECK)
Peak flow diary
Spirometry shows obstructive pattern (FEV1 <80% predicted, FEV1% <70%)
Reversibility: 4 puffs (400mg) of salbutamol, wait 15min, FEV should improve by 15% or
400ml. PEFR improves by 20%
CXR to rule out other causes
Management
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Short acting beta-2 agonist (Ventolin/salbutamol) for exacerbations. 1 puff per 30 seconds. If
need more than twice a week, is poorly controlled
o Act on beta-2 receptors, and cause smooth muscle relaxation
o Inhibit release of mediators from mast cells
Long acting beta-2 agonist – salmeterol, taken twice daily as adjunct therapy. Side effects:
tremor, tachycardia
Theophylline – given if beta agonists don’t work, also cause smooth muscle relaxation
Inhaled steroids – Glucocorticoids such as beclomethasone – act as anti-inflammatory drugs,
prevent Th2 recruitment of eosinophils and IgE release
Oral steroids – prednisolone – not routinely used, but can be if other options don’t work
Monoclonal antibodies – anti IgE: omalizumab, in allergic asthma and allergic rhinitis
Prognosis
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Many asthmatics have poor control, and poor inhaler technique
Asthma attack can be fatal
Brittle asthma: generally well controlled, but have flare ups and asthma attacks anyway