GP/ Medicine - Asthma Flashcards
What is asthma?
Chronic inflammatory disorder of the airways secondary to type 1 hypersensitivity, associated with increased airway responsiveness and airway obstruction that is reversible, either spontaneously or with bronchodilators
Give 5 risk factors for asthma
- Personal or family Hx of atopy e.g. asthma, allergic rhinitis (hayfever), allergic conjunctivitis, atopic dermatitis (eczema)
- Male sex for childhood asthma and female sex for adulthood asthma
- Smoking
- Antenatal factors e.g. maternal smoking, viral infection during pregnancy (esp RSV)
- Premature birth and low birth weight
- Not being breastfed
- Air pollution
- Occupational exposure to allergens e.g. flour dust and isocyanates from spray painting
Give 3 complications of asthma
Respiratory failure
Pneumothorax
Atelectasis
Pneumonia
Impaired quality of life e.g. fatigue, underperformance at school/ work
What is the pathophysiology of asthma?
It’s driven by Th2 cells
On first exposure with the allergen, the macrophages process and present the allergen to T cells, this activates particularly Th2 cells. The Th2 cells then release cytokines that activate mast cells, esoinophils, and B cells, which produce IgE. The IgE then plants itself onto the surface of mast cells.
The problem comes when the person is re-exposed to the same allergen, which triggers a 2-phase response:
- Immediate response (within 20 minutes) - type 1 hypersensitivity
- Caused by crosslinking of surface IgE receptors on mast cells upon binding to the allergen on re-exposure
- This leads to mast cell degranulation, causing a release of histamine, leukotrienes, and prostaglandin D2 –> bronchoconstriction
- Late phase response (3-12 hrs later) - type 4 hypersensitivity
- Inflammatory cells like the esoinophils, mast cells, T-lymphocytes, and neutrophils release cytokines that cause airway inflammation
- The eosinophils release leukotriene C4 that is toxic to airway epithelium and causes shedding of these cells, subepithelial fibrosis, and basement membrane thickening
The airway inflammation causes narrowing of the airway and reduced airflow due to:
- Mucosal oedema - due to histamine causing vasodilation and increased permeability of bvs
- Hyperplasia and hypertrophy of bronchial smooth muscles due to infiltration of inflammatory cells
- Bronchial smooth muscle contraction
- Over-production of thick mucus with impaired mucus clearance - due to increased numbers of goblet cells
- Mucus plugging in fatal and severe asthma
- Epithelium shed and form part of the thick mucus
What are the symptoms of asthma?
Symptoms:
- Dyspnoea
- Wheeze
- Chest tightness
- Dry cough that is worse at night (nocturnal)
- Sleep disturbance
- Acid reflux
- Diurnal variation of symptoms or peak flow
- Symptoms or peak flow may vary throughout the day. Marked deterioration of peak flow in the morning is common and can cause a serious asthmatic attack, despite having normal peak flows at other times
- Symptoms are brought on or exacerbated by exposure to cold air, allergens (pollen, dust mites, animal fur), exercise, stress, URTI (mainly viral), smoking (active/ passive), pollution, occupational irritants, and drugs e.g. aspirin, NSAIDs, beta-blockers
- Recent increase in the use of reliever inhalers with decreasing response
- Personal Hx/ FHx of atopy - asthma, allergic rhinitis, allergic conjunctivitis. eczema
What are the signs of asthma?
Signs:
Bilateral expiratory wheeze on auscultation
Tachycardia, tachypnoea
Cyanosis (if serious)
Decreased air entry
Hyperinflated chest
Hyperresonant percussion
What are the red flag signs and symptoms that suggest an alternative diagnosis to asthma and should prompt immediate referral to a respiratory physician for further investigations?
- Prominent systemic features (such as myalgia, fever, and weight loss).
- Unexpected clinical findings (such as crackles, finger clubbing, cyanosis, evidence of cardiac disease, monophonic wheeze, or stridor).
- Persistent, non-variable breathlessness.
- Chronic sputum production.
- Unexplained restrictive spirometry.
- Chest X-ray shadowing.
- Marked blood eosinophilia.
What are the trigger factors/ precipitants for asthma?
- Exposure to cold air
- Allergens
- Exercise
- Stress
- URTI (mainly viral)
- Smoking
- Pollution
- Occupational irritants
- Drugs e.g. aspirin, NSAIDs, beta-blockers
What examinations would you do for patients with suspected asthma?
- Respiratory and cardiovascular examination
Basic obs:
- Check HR, RR, BP, SaO2, temperature
The diagnosis of asthma is slightly different in different age groups. How would you diagnose asthma in patients >/= 17 years?
All patients >/= 5 years old need to have objective tests to diagnose asthma
For patients >/= 17 years old
- Rule out occupational asthma
- Ask patients if their symptoms are better on days away from work or during holidays. If so, patients should be referred to an occupational asthma specialist
- Spirometry
- If FEV1/ FVC < 70% (obstructive pattern) –> do a bronchodilator reversibility test (BDR)
- If BDR is positive i.e. there is an improvement in FEV1 of 12% or more and an increase in volume of 200 mL or more –> do a FeNO test
- If FeNO test is positive i.e. >/= 40 ppb –> the adult has asthma
- If FeNO test is negative –> monitor PEFRfor 2-4 weeks and check if there is variability
- If variable i.e. a diurnal variation of > 20% on >/= 3 days a week for 2 weeks –> the adult has asthma
- If not variable –> check if FeNO levels are 25-39 ppb
- If 25-39 ppb –> suspect asthma and review diagnosis after treatment
- If < 25 ppb –> consider other diagnoses or referral for a second opinion
- If BDR is negative –> do a FeNO test
- If FeNO test is positive i.e. >/= 40 ppb –> suspect asthma and review diagnosis after treatment
- If FeNO test is negative –> check if FeNO levels are 25-39 ppbIf
- If 25-39 ppb –> monitor PEFR for 2-4 weeks and check if there is variability
- If variable –> suspect asthma and review diagnosis after treatment
- If not variable –> check if there is airway hyperreactivity
- If yes –> the adult has asthma
- If no –> consider other diagnoses or referral for a second opinion
- If < 25 ppb –> consider other diagnoses or referral for a second opinion
- If 25-39 ppb –> monitor PEFR for 2-4 weeks and check if there is variability
- If BDR is positive i.e. there is an improvement in FEV1 of 12% or more and an increase in volume of 200 mL or more –> do a FeNO test
- If FEV1/ FVC > 70% (normal spirometry) –> do a FeNO test
- If FeNO test is positive i.e. >/= 40 ppb –> monitor PEFR for 2-4 weeks and check if there is variability
- If variable –> the adult has asthma
- If not variable –> check if there is airway hyperreactivity
- If yes –> the adult has asthma
- If no –> consider other diagnoses or referral for a second opinion
- If FeNO test is negative –> monitor PEFR for 2-4 weeks and check if there is variability
- If variable –> check if there is airway hyperreactivity
- If yes –> the adult has asthma
- If no –> consider other diagnoses or referral for a second opinion
- If not variable –> consider other diagnoses or referral for a second opinion
- If variable –> check if there is airway hyperreactivity
- If FeNO test is positive i.e. >/= 40 ppb –> monitor PEFR for 2-4 weeks and check if there is variability
- If FEV1/ FVC < 70% (obstructive pattern) –> do a bronchodilator reversibility test (BDR)
(PEFR- a diurnal variation of > 20% on >/= 3 days a week for 2 weeks)
Can also do a CXR- particular in older patients or those with a history of smoking –> show hyperinflated lungs, flattened hemidiaphragms, peribronchial cuffing, atelectasis
What should you do if diagnostic uncertainty remains after measuring PEFR variability?
Refer for a histamine or methacholine direct bronchial challenge test
(A positive test is PC20 = 8 mg/mL)
If the direct bronchial challenge test is unavailable, suspect asthma and review diagnosis after treatment OR refer to a centre with access to histamine or methacholine challenge testing
What bronchodilator do they use in spirometry?
Short-acting beta-2 agonist (Salbutamol)
How would you diagnose asthma in patients aged 5-16 years?
- Spirometry with a bronchodilator reversbility test
- Before bronchodilator –> FEV1/FVC < 70% (obstructive)
- After bronchodilator –> an improvement in FEV1 of 12% or more confirms the diagnosis of asthma in children
- Request FeNO test if there is normal spirometry or obstructive spirometry with a negative bronchodilator reversibility test
- PEFR
What is the next step in investigation if patient with suspected asthma has a negative result in spirometry (i.e. a normal spirometry or an obstructive spirometry with a negative bronchodilator reversibility test)?
A negative result in spirometry (i.e. a normal spirometry or an obstructive spirometry with a negative bronchodilator reversibility test) does not exclude asthma as a diagnosis, and should be further investigated with a FeNO test
How would you diagnose asthma in patients aged < 5 years old?
Diagnosis depends on clinical judgement
