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Asthma is characterised by episodes of breathlessness, wheeze, and cough. It affects 5-8% of the population and is on the increase. It is the most common chronic disease in children. Asthma is defined as episodes of reversible increase in airway resistance in response to irritant stimuli. Increased airway resistance is caused by (1) bronchial smooth muscle contraction, (2) mucosal inflammation, and (3) increased mucus production.

Acute asthma exacerbations can be fatal – see our guide on how to recognise and manage them.


Pathophysiology

Bronchial calibre is controlled by a balance between:

  • The sympathetic nervous system which causes bronchodilation and decreases mucous secretion via β2-adrenoceptors
  • The parasympathetic nervous system which causes bronchoconstriction and increases mucus secretion via M3-receptors

Mucosal inflammation involves T-helper cell activation and cytokine production. Attracted granulocytes (especially eosinophils) produce the spasmogens histamine, prostaglandin D2, and leukotrienes.


Signs and symptoms

Symptoms

Take a detailed clinical history looking for:

  • Wheeze, cough, breathlessness, or tight chest
  • Triggers – cold air, exercise, allergens, pollution, NSAIDs, ꞵ-blockers
  • Atopy – personal or family history of eczema, hay fever, allergic rhinitis
  • Exercise tolerance
  • Diurnal variation – symptoms and peak flow may be worse at night or early in the morning
  • Symptoms better on days off work? – Occupational asthma

Signs

Physical examination may reveal:

  • Expiratory polyphonic wheeze
  • Dry coughmay be nocturnal
  • Tachypnoea and hypoxia in acute severe asthma

Investigations

There is no one symptom, sign or test that is diagnostic of asthma. There are a number of useful investigations outlined below which help to diagnose asthma. They are used to demonstrate variable airway obstruction and airway inflammation to support a clinical assessment. If investigations are inconclusive, an asthma diagnosis may be ‘suspected’ – in this case, treatment should be initiated and monitored carefully by regular reviews. A good response to treatment supports an asthma diagnosis.

Adults

In adults with suspected asthma:

  1. Measure spirometry and FeNO test.
  2. Carry out a bronchodilator reversibility  (BDR) test if spirometry is positive.
  3. If the diagnosis is still uncertain, monitor peak expiratory flow (PEF) variability for 2-4 weeks.
  4. If the diagnosis is still uncertain, consider direct bronchial challenge test.

 

Children

In children ages 5-16 with suspected asthma:

  1. Measure spirometry.
  2. Carry out a BDR test if spirometry is positive.
  3. If the diagnosis is still uncertain, consider FeNO test.
  4. If the diagnosis is still uncertain, monitor PEF variability for 2-4 weeks.

 

Tests explained

TestWhat is it?Positive result
FeNO test Measures exhaled nitric oxide, which is a marker of eosinophilic inflammation.Adults: ppb ≥40

Children: ppb ≥35

Spirometry Measures volume of air expelled from the lungs after maximal inspiration.FEV1/FVC ratio < 70%
Bronchodilator reversibility (BDR)Measures change in spirometry before and 15 minutes after SABA inhalation.Improvement in FEV1 of ≥ 12%
Peak expiratory flow (PEF) Measures maximum speed of expiration. Monitor twice daily for 2-4 weeks.Variability ≥ 20%
Direct bronchial challenge test Measures change in spirometry after methacholine/histamine inhalation.8mg/mL or less causing a ≥ 20% drop in FEV1

Diagnosis

Diagnose asthma in:

  • Adults with symptoms and positive investigation results.
  • Children aged 5-16 with symptoms and positive investigation results.
  • Children under 5 on signs and symptoms alone. Review them on a regular basis and carry out investigations if they are still symptomatic when they reach 5 years.

Differential diagnoses

  • Bronchiectasis
  • COPD
  • Cystic fibrosis
  • Airway obstruction (foreign body, tumour)
  • Pulmonary oedema
  • GORD
  • Pulmonary embolism

Managing chronic asthma

Non-pharmacological management includes advice on smoking cessation and weight loss in overweight/obese patients. Advise patients to avoid asthma triggers where possible.

There is clear guidance on the stepwise pharmacological management of asthma. Management is based on (1) bronchodilator ‘relievers’ and (2) anti-inflammatory ‘preventers’.

Short-acting β2-agonist (SABA)

  • e.g. Salbutamol, as required
  • Mechanism of action: β2-agonism causes bronchial smooth muscle relaxation which dilates bronchi to improve airflow in obstructed airways.
  • Adverse effects: Tremor is the most common unwanted effect. Others include tachycardia, palpitations, and cardiac dysrhythmia.

Low dose inhaled corticosteroid (ICS)

  • e.g. Beclometasone, twice daily
  • Mechanism of action: Corticosteroids reduce leukocyte proliferation and downregulate pro-inflammatory cytokine, leukotriene, and chemokine production. This reduces mucosal inflammation, dilates airways, and reduces mucous secretion.
  • Adverse effects: Oral candidiasis is the main unwanted effect. They can also cause a hoarse voice. Regular high dose steroid use can cause adrenal suppression, especially in children – monitor their growth annually.

 

β2-agonists and inhaled corticosteroids form the basis of chronic asthma management. They should be offered as first-line treatments to all adults and children over the age of 5.

If symptoms remain uncontrolled, add-on therapies can be considered. Before initiating an add-on therapy, recheck adherence, inhaler technique, and elimination of trigger factors.

Add-on therapies

  1. Leukotriene receptor antagonist (LTRA)oral therapy taken at night to downregulate inflammatory leukotrienes
  2. Long-acting β2-agonist (LABA) – must always be given in combination with ICS
  3. Medium dose inhaled corticosteroids
  4. Trial of additional drugs – theophylline or a long-acting muscarinic antagonist (LAMA)
  5. High dose inhaled corticosteroids

Counselling

  • For all inhalers: Proper inhaler technique is very important, and poor technique is the most common reason for uncontrolled asthma.
  • For SABA: Ensure the patient knows how and when to take the inhaler (e.g. for acute symptoms, preemptively before exercise). They should understand that this treats symptoms, not the disease.
  • For ICS: A spacer should be used with ICS therapy to improve deposition and reduce the risk of oral candidiasis. Also, advise the patient to rinse their mouth and gargle after use. Reassure the patient that little steroid is absorbed into the blood so systemic effects are minimal.
  • Interactions: NSAIDs may provoke asthma (by inhibiting the COX pathway they promote arachidonic acid conversion to leukotrienes). Beta-blockers are contraindicated in asthma as they reduce the effectiveness of β2-agonists.

References

  1. NICE Clinical Knowledge Summary – Asthma [LINK]
  2. BTS/SIGN British Guideline on the Management of Asthma [LINK]
  3. Oxford handbook of clinical medicine 10th edition

 

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