Asthma

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Introduction

Asthma is defined as episodes of a reversible increase in airway resistance in response to irritant stimuli.

Increased airway resistance is caused by bronchial smooth muscle contraction, mucosal inflammation, and increased mucus production.

Asthma is characterised by episodes of breathlessness, wheeze, and cough. It affects 5-8% of the population and is the most common chronic disease in children.

Acute asthma exacerbations can be fatal. For an overview of acute asthma, see the Geeky Medics guide to the emergency management of asthma


Aetiology

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.


Clinical features

History

Typical symptoms of asthma include:

  • Wheeze
  • Cough
  • Breathlessness
  • Chest tightness

Symptoms may have diurnal variation (worse at night and early in the morning) and be episodic

Other important areas to cover in the history include:

  • Past medical history: history of atopy (e.g. eczema or allergic rhinitis) or asthma
  • Social history: occupation (occupational asthma)
  • Triggers: common triggers include cold air, exercise, allergens, pollution, NSAIDs and ꞵ-blockers

For more information, see the Geeky Medics guide to taking a respiratory history

Clinical examination

Patients with suspected asthma require a thorough respiratory examination

Typical clinical findings include:

  • Expiratory polyphonic wheeze
  • Dry cough: may be nocturnal
  • Tachypnoea and hypoxia in acute severe asthma

Investigations

There is no one symptom, sign or test that is diagnostic of asthma, however, there are several useful investigations outlined below that help to diagnose asthma.

Investigations 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:

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

Children

In children aged 5 – 16 with suspected asthma:

  • Perform spirometry
  • Carry out a bronchodilator reversibility (BDR) test if spirometry is positive
  • If the diagnosis is still uncertain, consider a FeNO test
  • If the diagnosis is still uncertain, monitor peak expiratory flow variability for 2-4 weeks

Overview of asthma investigations

Table 1. An overview of the available investigations for asthma.

Test Description 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 the 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

Differential diagnoses to consider in the context of asthma include:

  • Bronchiectasis
  • COPD
  • Cystic fibrosis
  • Airway obstruction (foreign body, tumour)
  • Pulmonary oedema
  • Gastro-oesophageal reflux disease
  • Pulmonary embolism

Management

Non-pharmacological management

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

Pharmacological management

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

β2-agonists (‘relievers’) and inhaled corticosteroids (‘preventers’) form the basis of chronic asthma management. They should be offered as first-line treatments to all adults and children over the age of five.

Short-acting β2-agonist (SABA)

β2-agonism causes bronchial smooth muscle relaxation which dilates bronchi to improve airflow in obstructed airways. Salbutamol is the most used SABA. 

Tremor is the most common adverse effect. Others include tachycardia, palpitations, and cardiac dysrhythmia.

Low dose inhaled corticosteroid (ICS)

Corticosteroids reduce leukocyte proliferation and downregulate pro-inflammatory cytokine, leukotriene, and chemokine production. This reduces mucosal inflammation, dilates airways, and reduces mucous secretion. An example of an ICS is beclomethasone.

Oral candidiasis is the main adverse effect. They can also cause a hoarse voice. Regular high dose steroid use can cause adrenal suppression, especially in children. 

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

Additional therapies aside from SABA and ICS include:

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

It is important to provide information for patients on asthma and their management: 

  • For all inhalers: proper inhaler technique is especially 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, pre-emptively 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.

Complications

Complications of asthma include:

  • Asthma exacerbations: can lead to respiratory failure and death
  • Respiratory complications: airway remodelling and persistent airway obstruction
  • Complications related to corticosteroids: oral candidiasis, adrenal suppression and growth suppression
  • Psychosocial impact: missed school/social activities

Key points

  • Asthma is defined as episodes of a reversible increase in airway resistance in response to irritant stimuli.
  • Asthma is characterised by episodes of breathlessness, wheeze, and cough. It affects 5-8% of the population and is the most common chronic disease in children.
  • Symptoms may have diurnal variation (worse at night and early in the morning) and be episodic
  • Investigations are used to demonstrate variable airway obstruction and airway inflammation to support a clinical assessment. Options include spirometry, exhaled nitric oxide and peak flow monitoring.
  • There is clear guidance on the stepwise pharmacological management of asthma. Management is based on bronchodilator ‘relievers’ and anti-inflammatory ‘preventers’.
  • It is important to provide information for patients on asthma and their management.

Editor

Dr Chris Jefferies


References

  1. NICE Clinical Knowledge Summary. Asthma. Available from: [LINK]
  2. BTS/SIGN. British Guideline on the Management of Asthma. Available from: [LINK]

 

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