Pathophysiology
Asthma occurs due to a reversible airway obstruction.
The pathophysiology of asthma includes airway narrowing due to bronchial muscle contraction, inflammation caused by mast cell degranulation and increased mucus production.
Symptoms of asthma
- Wheeze
- Dyspnoea
- Cough (may be nocturnal)
- Chest tightness
- Diurnal variation (symptoms often worse in the morning)
- Note: a personal/family history of atopy may be present, and symptoms may worsen following exercise or NSAIDs/beta-blockers
Signs of asthma
- Tachypnoea
- Hyperinflated chest
- Hyper-resonance on chest percussion
- Decreased air entry (sign of severe illness: silent chest)
- Wheeze on auscultation
- Signs of a severe attack: inability to speak in complete sentences, respiratory rate >25, peak flow 33-50% predicted
- Signs of a life-threatening attack: silent chest, confusion, bradycardia, cyanosis, exhaustion
Investigations in acute asthma
he following investigations should be ordered more urgently in the context of an acute asthma attack.
- ABG: type 2 respiratory failure (low PaO2 and high PaCO2) is a sign of a life-threatening attack.
- Routine blood tests (including FBC, CRP): to look for precipitating causes of an asthma attack, such as an infection.
- Chest x-ray: to exclude differentials and possibly identify a precipitating
Investigations in chronic asthma
- Peak flow: variability >20%
- Fractional exhaled nitric oxide (FeNO): >40 ppb in adults or >35 ppb in children
- Spirometry: FEV1/FVC <0.7 (obstructive spirometry)
- Bronchodilator reversibility tests: Improvement of FEV1 >12% after bronchodilator therapy is diagnostic
- History-
- Day to day diurnal variability.
- Episodic symptoms.
- Relationship to exposures.
- Occupational / irritants.
Management of an acute asthma attack
- Ensure a patent airway
- Ensure oxygen saturations of 94-98%
- Nebulisers: Salbutamol, Ipratropium
- Steroids: oral Prednisolone or IV Hydrocortisone (if severe)
- IV Magnesium Sulphate: if severe
- IV aminophylline: if severe and inadequate bronchodilatory response from nebulisers
- If the patient does not improve following these measures, intensive care input will be required for consideration of an intensive care admission which may involve invasive ventilation.
Non-pharmacological management of chronic asthma
- Smoking cessation
- Avoidance of precipitating factors (eg. known allergens)
- Review inhaler technique
pharmacological management of chronic asthma
stepwise approach
Step 1: short-acting inhaled B2-agonist SABA (eg. Salbutamol)
Step 2: add low-dose inhaled corticosteroid steroid (ICS)
Step 3: add long-acting B2-agonist LABA (eg. Salmeterol). If no benefit, stop this and increase ICS dose; if benefit but inadequate control, continue and increase ICS dose.
Step 4: Trial oral leukotriene receptor antagonist, high-dose steroid, oral B2-agonist
Risk factors
- Personal or family history of atopy
- Antenatal factors; maternal smoking, viral infection during pregnancy (especially RSV)
- Low birth weight
- Not being breastfed
- Exposure to high concs of allergens
- Air pollution
“Hygiene hypothesis”
increased risk of asthma and other allergic conditions in developed countries. Reduced exposure to infectious agents in childhood prevents normal development of the immune system resulting in Th2 predominant response.
Associated atopic conditions: IgE mediated
- Atopic dermatitis (eczema)
- Allergic rhinitis (hay fever)
What is FEV1 and FVC
effect of asthma of FEV1 and FVC
FEV1: forced expiratory volume- volume that has been exhaled at the end of the first second of forced expiration
FVC: forced vital capacity- volume that has been exhaled after a maximal expiration following a full inspiration
differntial diagnoses for wheeze
- COPD- fixed airflow obstruction
- Upper airway obstruction- stridor
- Foreign body
- HYpernventilation syndrome
- Anxiety
- Gastro-oesophageal syndrome
- Pulmonary oedema
- Eosinophilic vasculitis
- Respiratory bronchiolitis
new alternative therapies for asthma management
- MART therapies- fostair
- Omaluzimab- monoclonal antibody of IgE
- Reslizumab- monoclonal antibody to Il5
- Mepoluzimab- monoclonal antibody to Il-5 (s/c/)
- Benralizumab- Il-5
- Bronchial thermoplasty- diathermy bronchial smooth muscle
