Asthma Flashcards
Definition
“Chronic inflammatory disorder of the airways that gives rise widespread airway narrowing and airway hyper-responsiveness”.
Extrinsic asthma
Most common
• 90% of cases in children
• 70% in adults.
• Associated with atopy, where there is evidence
of sensitisation to a particular allergen.
• Most common inhaled allergens are dust mite
faeces, animal dander, pollens, and fungi.
• Patients usually have history of eczema or
allergic rhinitis.
Intrinsic asthma
Associated with older age (i.e. ‘late-onset
asthma’).
• Not associated with an allergic cause.
• Stress, exercise, cold air, smoke,
environmental irritants, viral infections, and
some drugs are potential triggers.
Aetiology
Thought to be due to a combinain of envionmental factos and genetic predisposition
- Genetic factors: ADAM33, GPRA (G-protein related receptor for asthma), ORMDL3
- Environmental factors:
Hygiene hypothesis → Early exposure to bacterial endotoxin switches off the allergic Th2 response and favours the protective Th1 response instead. When this exposure is lost (i.e. as a result of ‘first-world’ cleanliness) it can lead to the development of conditions such as asthma, eczema, and allergic rhinitis.
Symptoms of asthma
- intermittent dyspnoea
- wheeze
- cough often nocturnal
precipitants: cold air, exercise, emotion, allergens, infection, smoking and passive smoking
Diurnal variation: in symptoms or peak flow. Marked morning dipping of peak flow is common
Exercise
Disturbed sleep: quantify as nights per week
Acid reflux: 40-60% of those with asthma
other atopic disease: eczema, hay fever, or family history
The home: pets, carpets, feather pillows or duvet
Job: If symptoms remit at weekends or holidays
SIGNS
- tachypnoea
- audible wheeze
- hyperinflated chest
- hyperresonant percussion
Diagnosis
The diagnosis of asthma is based on the recognition of a characteristic pattern of symptoms and signs and the absence of alternative explanation
Asthma investigations (chronic)
Confirmation hinges on demonstration of airflow obstruction (FEV1/FVC <0.7)
varying over short periods of time. Spirometry, which is now becoming more
widely available, is preferable to measurement of PEF because it allows clearer
identification of airflow obstruction, and the results are less dependent on
effort.
Of note, a normal spirogram (or PEF) obtained when the patient is not
symptomatic does not exclude the diagnosis of asthma.
- serial PEF monitoring - diurnal variation of >20% on >3d per week for 2 weeks
- Spirometry - obstructive defect ( decreased FEV1/FVC) usually 15% (>40ml improvement in FEV1 following B2 agonists
- CXR
- Skin prick test - allergens
- Metacholine or histamine bronchial provocation test - look for a drop of 20 % in FEV1 from baseline
- Exhaled nitric oxide - a marker of airway inflammation (raised level > 25 ppb)
- Blood and sputum tests - may have raised blood eosinophils, often have raise sputum eosinophils but not routinely done
Radiograhic findings
Plain films can be normal in up to 75% of patients
Reported features:
- Pulmonary hyperinflation
- Bronchial wall thickening (non specific but maybe present in around 48% asthmatics)
- Pulmonary oedema (rare) due to acute asthma
CT Chest/HRCT chest
CT is usually use to detect the presence of complicated associated conditions such as ABPA and not to directly diagnose.
Reported HRCT features of asthma are non specific
they include :
• bronchial wall thickening
• expiratory air trapping
• inspiratory decreased lung attenuation
• bronchial luminal narrowing
• subsegmental
Management of chronic asthma
Step 1: occasional relief bronchodilator: Inhaled short-acting beta2 agonist as required (up to once daily)
Step 2: regular inhaled preventer therapy - inhaled corticosteroid
Step 3: inhaled corticosteroid + long-acting inhaled beta2 agonist
If long-acting beta2 agonist stopped (not working, not tolerated), add one of
- Leukotriene receptor antagonist
- Modified-release oral theophylline
- Modified-release oral beta2 agonist; child under 12 years not recommended
Step 4: high-dose inhaled corticosteroid + regular bronchodilators e.g. nebulised therapy, anti-muscarinics
Step 5: regular corticosteroid tablets
If still not controlled, then other possible therapies Anti-IgE therapy (Omalizumab), methotrexate, ciclosporin, anti-TNFa treatments (Etanercept) – considered at specialist asthma clinics
Assess the severity of an acute asthmatic attack
management of acute asthma
drugs used in acute asthma
- Salbutamol - B2 agonist
- hydrocortisone and prednisolone - reduces inflammation
- Aminophylline - Inhibits phosphodiesterase; increases cAMP
Subsequent management
Repeat PEF 15-30 minutes after starting treatment.
• Repeat ABG 1 hours after starting treatment.
• Transfer to ICU if worsening signs or symptoms.
Discharge when following criteria are met:
• Patient has been on discharge medication for > 24 hours.
• Inhaler technique has been checked.
• PEF is > 75% of best or predicted and PEF diurnal variability is < 25%.
• GP follow-up appointment has been arranged within 2 working days.
• Respiratory clinic follow-up appointment has been arranged within 4 weeks.
