Asthma Resources

There are some very useful clinical asthma resources worth reviewing. I recommend you look at the Australian Asthma Handbook developed by the National Asthma Council.  It is available from https://www.asthmahandbook.org.au/.   You should also familiarise yourself with eTherapeutic Guidelines available through the JCU library database.

Pathophysiology

Asthma is a chronic, inflammatory disorder of the airways involving reversible airway obstruction.  Asthma occurs due to inappropriate inflammation and hyperresponsiveness to triggers.  These stimuli may include any of the following:

• Environmental triggers (e.g., smoke, allergens, cold or dry air, perfumes)
• Pharmacological triggers (e.g., NSAIDs, aspirin, beta blockers and cholinergic agents)
• Exercise
• Physiological and psychological changes (e.g. extreme emotions, hormonal changes, pregnancy and sexual activity)

In response to these stimuli, a range of inflammatory mediators are released.  The release of eosinophils, leukotrienes and leucocytes cause bronchoconstriction of airway smooth muscle, bronchiole oedema and mucous production, which narrows the airway and limits the passage of air to alveoli for gas exchange.  Additionally, these inflammatory mediators also produce a sub-acute inflammatory response leading to permanent airway remodeling.  Permanent airway remodeling can involve increased collagen deposition, thickening of basement membrane and increase in expression of goblet cells.  

Symptoms of airway obstruction associated with asthma include:

• Cough
• Wheeze
• Breathlessness
• Chest discomfort or tightness
• Increased respiratory rate and work of breathing (in children)

Asthma is linked to a history of atopic disorder (allergic rhinitis or atopic dermatitis) and a family history  of asthma or atopic disorder.

There are 3 different phenotypes of asthma.  These include allergic asthma, late-onset asthma and aspirin-exacerbated respiratory disease (AERD).

Epidemiology

Asthma is a common chronic condition in children, with about 1 in 10 boys and 1 in 16 girls under 15 years having asthma.  Asthma has a major impact on individuals, their carers and Australia’s health system. In 2022-2023 there were over 31,000 hospitalisations where asthma was the main diagnosis.  Almost half (43%) of these were for children aged 14 or under.  Over 90% of asthma hospitalisations were considered potentially avoidable with optimised care in the community.  People with asthma are more likely to report a poor quality of life, especially those with severe or poorly controlled asthma.  In 2020-21, asthma directly cost the health system $852 million for services provided through general practice, hospitals, government funded medicines, dental services and referrals to specialists and testing.  A recent study estimated that poorly controlled asthma costs the healthcare system about $4,600 per person per year.  There were 474 deaths due to asthma in 2023.

Diagnosis of Asthma In Adults, Adolescents and Children > 6 years

The diagnosis of asthma in adults, adolescents and school-aged children is based on clinical assessment supported by lung function tests.  Firstly, a clinical history and examination can determine the likely probability that symptoms (such as cough, chest tightness, wheeze and shortness of breath) and clinical findings are due to asthma.  Then, confirmation of the diagnosis can occur via lung function tests that are used at a time when the patient does not have a respiratory tract infection.  Spirometry is key to confirm a diagnosis of asthma.  It should be arranged and performed for every adult patient, adolescent and child > 6 years with suspected asthma.  You should remember from the previous chapter that spirometry is used to measure FEV₁ and FVC and can be performed  before and after administration of a bronchodilator, such as salbutamol via a spacer.

Spirometry findings that would support a diagnosis of asthma in adults and adolescents include:

• Expiratory airflow limitation demonstrated by FEV₁/FVC ratio less than lower limit of normal for age
• Expiratory airflow limitation that is reversible (variable) demonstrated by an increase in FEV₁ of at least 200 mL and 12% from baseline 10 to 15 minutes after giving a short-acting beta₂ agonist. A larger increase in FEV₁ (eg more than 400 mL) in response to a SABA is strongly supportive of asthma.

In school-aged children (6-11 years) who are able to perform spirometry, the diagnosis of asthma is supported by finding of:

• Expiratory airflow limitation that is reversible (variable) demonstrated by FEV₁ increase ≥12% from baseline post bronchodilator.

Patients with asthma typically show significant reversibility of the obstructive symptoms of asthma (i.e. variation in expiratory airflow that is greater than that seen in healthy patients).  In the diagram below, you can see that there is in improvement in FVC and FEV₁ after exposure to a bronchodilator (salbutamol = green line).  The evidence for variable airflow limitation must be documented at the time of asthma diagnosis in adults, adolescents and children > 6 years.

Look at the “Steps in the diagnosis of asthma in adults” from the National Asthma Handbook.  It is also available here: Figure_Steps-in-the-diagnosis-of-asthma-in-adults_web. 

Then, look at the “Steps in the diagnosis of asthma in children aged 6 years and over”.  It is also available here: Figure_Steps-in-the-diagnosis-of-asthma-in-children-aged-6-years-and-over_web_LR