Asthma is a chronic inflammatory airway disease leading to variable airway obstruction. The smooth muscle in the airways is hypersensitive and responds to stimuli by constricting, narrowing the space for air to flow through. This bronchoconstriction is reversible with bronchodilators, such as inhaled salbutamol.
Asthma is one of several atopic conditions, including eczema, allergic rhinitis (e.g., hay fever) and food allergies. Patients with one of these conditions are more likely to have others. These conditions characteristically run in families.
Acute asthma exacerbations involve rapidly worsening symptoms and can quickly become life-threatening.
Presentation
Symptoms are episodic, meaning there are periods where the symptoms are worse and better. There is diurnal variability, meaning the symptoms fluctuate at different times of the day, typically worse at night.
Typical symptoms are:
- Shortness of breath
- Chest tightness
- Dry cough
- Wheeze
Symptoms should improve with bronchodilators. No response to bronchodilators reduces the likelihood of asthma.
Examination is generally normal when the patient is well. A key finding with asthma is a widespread “polyphonic” expiratory wheeze.
Typical Triggers
Specific environmental triggers can exacerbate the symptoms of asthma:
- Viral infections
- Exercise
- Animals
- Cold, damp or dusty air
- Strong emotions
TOM TIP: Beta blockers, particularly non-selective beta blockers (e.g., propranolol), and non-steroidal anti-inflammatory drugs (e.g., ibuprofen or naproxen), can exacerbate asthma.
Investigations
Fractional exhaled nitric oxide (FeNO) measures the concentration of nitric oxide exhaled by the patient. Nitric oxide is a marker of airway inflammation. The test involves a steady exhale for around 10 seconds into a device that measures FeNO. Smoking can lower the FeNO, making the results unreliable. The cutoff depends on the age:
- Aged over 16: 50 or greater ppb
- Age 5-16: 35 or greater ppb
Eosinophil count on a blood test (full blood count) is often raised in asthma and allergic conditions.
Spirometry is used to objectively measure the lung function. It involves different breathing exercises into a machine that measures volumes of air and flow rates. A FEV1:FVC ratio of less than 70% suggests obstructive pathology (e.g., asthma or COPD).
Reversibility testing involves giving a bronchodilator (e.g., salbutamol) before repeating the spirometry to see if this impacts the results. NICE says a greater than 12% increase in FEV1 on reversibility testing supports a diagnosis of asthma.
Peak flow variability is measured by keeping a peak flow diary with readings at least twice daily over 2 to 4 weeks. NICE says a peak flow variability of more than 20% is a positive test result, supporting a diagnosis.
Direct bronchial challenge testing is the opposite of reversibility testing. Inhaled histamine or methacholine is used to stimulate bronchoconstriction, reducing the FEV1 in patients with asthma.
Diagnosis
A diagnosis of asthma requires a suggestive clinical history plus objective testing. Where the history is suggestive, but the initial tests are inconclusive, additional tests are organised until the diagnosis is confirmed or excluded.
Adults and children over 16:
- Initially FeNO or eosinophil count
- Then reversibility testing with spirometry
- Then peak flow diary twice daily for 2 weeks
- Then bronchial challenge test
Children aged 5-16:
- Initially FeNO
- Then reversibility testing with spirometry
- Then peak flow diary twice daily for 2 weeks
- Then skin prick testing to house dust mite or bloods for total IgE and eosinophil count
Children under 5 with suspected asthma are treated until they are 5 years old, after which objective tests are performed. This involves an 8-12 week trial of a regular inhaled corticosteroid to see if symptoms resolve during this trial. Children in this age group often have viral-induced wheeze rather than asthma.
Pharmacology
Beta-2 adrenergic receptor agonists are bronchodilators (they open the airways). Adrenaline acts on the smooth muscle of the airways to cause relaxation. Stimulating the adrenaline receptors dilates the bronchioles and reverses the bronchoconstriction present in asthma. (This is why non-selective beta blockers can worsen asthma symptoms). Key side effects include tachycardia and tremor.
Short-acting beta-2 agonists (SABA), such as salbutamol, work quickly, but the effects last only a few hours. They are used as reliever or rescue medication during an acute worsening of symptoms. Long-acting beta-2 agonists (LABA), such as salmeterol, are slower to act but last longer.
Inhaled corticosteroids (ICS), such as beclometasone, reduce the inflammation and reactivity of the airways. These are used as maintenance or preventer medications to control symptoms long-term and are taken regularly, even when well. A key side effect is oral candidiasis (thrush).
Long-acting muscarinic antagonists (LAMA), such as tiotropium, work by blocking acetylcholine receptors. Acetylcholine receptors are stimulated by the parasympathetic nervous system and cause contraction of the bronchial smooth muscles. Blocking these receptors dilates the bronchioles and reverses the bronchoconstriction present in asthma. A key side effect is dry mouth.
Leukotriene receptor antagonists, such as montelukast, work by blocking the effects of leukotrienes. Leukotrienes are produced by the immune system and cause inflammation, bronchoconstriction and mucus secretion in the airways. A key side effect is neuropsychiatric reactions, particularly nightmares.
Anti-inflammatory reliever (AIR) therapy involves a dry powder inhaler containing an inhaled corticosteroid (e.g., budesonide) plus a fast and long-acting beta-agonist (e.g., formoterol). This is used when required for symptoms in patients who do not take any other asthma treatment or regular inhalers. Each time the patient uses it to relieve asthma symptoms, they receive a dose of ICS.
Maintenance and reliever therapy (MART) involves a dry powder inhaler containing an inhaled corticosteroid (e.g., budesonide) plus a fast and long-acting beta-agonist (e.g., formoterol). The patient uses this single inhaler regularly as a preventer and reliever when they have symptoms. They get a regular ICS and beta-agonist dose, with additional doses for uncontrolled symptoms.
Long-Term Management Under 5 Years
Initial management involves:
- Regular low-dose inhaled corticosteroid
- Short-acting beta-2 agonist inhaler (e.g. salbutamol) as required
The next steps if their symptoms remain uncontrolled, escalating as needed to control symptoms, are:
- Regular moderate-dose inhaled corticosteroid
- Add oral leukotriene receptor antagonist (e.g. montelukast)
Long-Term Management 5 – 11 Years
Initial management involves:
- Regular low-dose inhaled corticosteroid
- Short-acting beta-2 agonist inhaler (e.g. salbutamol) as required
If their asthma remains uncontrolled, there is a choice between the MART or conventional pathways.
MART pathway:
- Low-dose MART
- Moderate-dose MART
- Specialist referral
Conventional pathway:
- Add oral leukotriene receptor antagonist (e.g. montelukast)
- Regular low-dose ICS + LABA combination inhaler
- Regular moderate-dose ICS + LABA combination inhaler
- Specialist referral
Long-Term Management Aged 12 and Older
The treatment steps in those aged over 12 (including adults), escalating as needed to control symptoms, are:
- AIR therapy
- Low-dose MART
- Moderate-dose MART
- Specialist referral if FeNO or eosinophils are raised at this stage
- Add leukotriene receptor antagonist or LAMA (8-12 week trial and switch if not helping)
- Specialist referral
Inhaled Corticosteroids And Growth
There is evidence that inhaled steroids can very slightly reduce growth velocity and may cause a slight reduction in final adult height of up to 1cm when used long-term (for more than 12 months). This effect is dose-dependent, meaning it is less of a problem with smaller doses.
However, inhaled corticosteroids are effective in preventing poorly controlled asthma. Asthma attacks can lead to higher doses of oral steroids being given. Poorly controlled asthma can have a greater impact on growth and development than inhaled steroids. Regular reviews are implemented to ensure they are on the correct dose.
Inhaler Technique
Inhaler technique is a key aspect of good asthma management. The better the technique, the more medication reaches the lungs. Poor technique results in medication in the mouth or the back of the throat. This reduces the effectiveness of the medication and leads to complications such as oral thrush.
Ideally, inhalers should be used with a spacer device to maximise their effectiveness. There are multiple types of inhaler, with different techniques. This focuses on the technique used for the typical salbutamol metered dosed inhaler (MDI). Dry powder inhalers require the patient to inhale quickly and deeply to draw the powder into the lungs.
MDI technique without a spacer:
- Remove the cap
- Shake the inhaler (depending on the type)
- Sit or stand up straight
- Lift the chin slightly
- Fully exhale
- Make a tight seal around the inhaler between the lips
- Take a steady breath in whilst pressing the canister
- Continue breathing in for 3 – 4 seconds after pressing the canister
- Hold the breath for 10 seconds (or as long as comfortably possible)
- Wait 30 seconds before any further doses
- Rinse the mouth after using a steroid inhaler
MDI technique with a spacer:
- Assemble the spacer
- Shake the inhaler (depending on the type)
- Attach the inhaler to the correct end
- Sit or stand up straight
- Lift the chin slightly
- Make a seal around the spacer mouthpiece or place the mask over the face
- Spray the dose into the spacer
- Take steady breaths in and out 5 times until the mist is fully inhaled
Alternatively, exhale fully before making a seal with the spacer, spray the dose, and take one deep breath to inhale the full mist before holding it for 10 seconds.
Spacers are cleaned once a month with warm water and washing up liquid. They should avoid scrubbing the inside and allow the spacer to air dry to avoid creating static. Static can interact with the mist and prevent the medication from being inhaled.
TOM TIP: Practise teaching inhaler technique for OSCEs. Check inhaler technique during asthma reviews. In someone with poorly controlled asthma, consider whether their inhaler technique is adequate.
Acute Exacerbation
An acute exacerbation of asthma involves a rapid deterioration in asthma symptoms. Typical asthma triggers, such as infection, exercise or cold weather, may be implicated.
Acute asthma presents with rapidly worsening symptoms of:
- Shortness of breath
- Tachypnoea (raised respiratory rate)
- Signs of respiratory distress (e.g., recessions and tracheal tug)
- Widespread expiratory wheeze on auscultation
Severe features:
- Peak flow 33-50% best or predicted
- Oxygen saturations less than 92%
- Raised respiratory rate (above 40 if 1-5 years, above 30 if over 5 years)
- Raised heart rate (above 140 if 1-5 years, above 125 if over 5 years)
- Unable to complete sentences
Life-threatening features:
- Peak flow less than 33%
- Exhausted or drowsy
- Confused
- Cyanosis
- Hypotension
- Silent chest (the wheeze disappears when the airways are so tight that there is no air entry)
Management of Acute Asthma
Patients with an acute exacerbation of asthma can deteriorate quickly. Acute asthma is potentially life-threatening. Treatment should be aggressive and involve early escalation to seniors and intensive care.
Moderate exacerbations may be treated with:
- Inhaled beta-2 agonists (e.g., salbutamol)
- Consider steroids (e.g., oral prednisolone) for 3-5 days
Salbutamol inhalers are given via a spacer. High doses are used initially and gradually stepped down as tolerated, reducing the dose and increasing the space between doses. One puff at a time, every 30-60 seconds. For example:
- 10 puffs every 2 hours
- 10 puffs every 4 hours
- 6 puffs every 4 hours
- 4 puffs every 6 hours
Severe exacerbations may additionally be treated with:
- Oxygen to maintain sats 94-98%
- Nebulised beta-2 agonists (e.g., salbutamol)
- Nebulised ipratropium bromide
If not responding to treatment, additional options include:
- IV magnesium sulphate
- IV salbutamol
- IV aminophylline
Life-threatening exacerbations may require:
- HDU or ICU
- Intubation and ventilation
The decision to intubate a patient with life-threatening asthma is made early, as it is challenging to intubate with severe bronchoconstriction.
High doses of salbutamol can cause side effects of tachycardia and tremor.
Discharge is considered when the patient is stable on four hourly inhalers. Patients are given a written asthma action plan, and follow-up is arranged with their GP and asthma clinic.
Last updated February 2025
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