17th February 2025

Asthma

Diagnosis of asthma

Clinical features of asthma

Asthma is a clinical diagnosis; there is no singular definition but criteria normally include:

• Presence of episodic symptoms (cough, breathlessness, wheeze, chest tightness)
• Variable airflow obstruction
• Evidence of airway inflammation

Table 1 Clinical features with a high and low predictive value for asthma

Investigations in chronic asthma

With a typical clinical picture of asthma, treatment can be initiated with inhaled corticosteroids (usually a 6-week trial). If there is a good objective response (shown using lung function tests or symptom scores), the diagnosis can be confirmed. Otherwise, investigations include the following:

• Spirometry with bronchodilator reversibility test:
  • FEV1/FVC <70%, i.e. an obstructive picture
  • Post-bronchodilator >12% improvement in FEV1 or >200 ml increase in volume
• Fractional exhaled nitrous oxide (FeNO): >40 parts per billion (a marker of airway inflammation)

Occupational asthma

Common triggers for occupational asthma include isocyanates (in spray paint, adhesives), resins and flour. To make the diagnosis, patients should record peak flow measurements at work and home. This diagnosis requires referral to a respiratory specialist.

Management of chronic asthma

Both the BTS (British Thoracic Society) 2019 guidelines and NICE 2017 guidelines cover the management of acute asthma. The following is a summary of the NICE stepwise management of asthma:

• Step 1 (new diagnosis): short-acting beta-2 agonist (SABA)
• Step 2 (not controlled with SABA or new diagnosis of asthma with moderate/severe symptoms, e.g. nighttime waking or frequent exacerbations): SABA + low-dose inhaled corticosteroid (ICS)
• Step 3: SABA + low-dose ICS + leukotriene receptor antagonist (LTRA)
• Step 4: SABA + low-dose ICS + long-acting beta agonist (LABA); continue LRTA if good response, otherwise stop
• Step 5: SABA ± LTRA; switch ICS + LABA for maintenance and reliever therapy (MART) including a low-dose ICS
• Step 6: SABA ± LTRA + medium-dose ICS MART
• Step 7: SABA ± LTRA + one of: high-dose ICS (fixed-dose regimen, not as a MART) or trial of long-acting muscarinic receptor antagonist (LAMA) or theophylline; referral to specialist asthma service

Guidelines by BTS are very similar, although they advise prescribing a leukotriene receptor antagonist in step 4 rather

Box 1 Common medications used in asthma

Box 2 ICS dosing

Acute asthma

Definitions in acute asthma

NICE guidance advises that acute asthma attacks be graded by severity using criteria such as peak flow, observations such as heart rate and respiratory rate, ABG (arterial blood gas) results and clinical symptoms.

Patients presenting with severe or life-threatening asthma attacks should be started on asthma treatment immediately and should be treated in secondary care facilities. Patients with moderate asthma attacks can be trialled on treatment at home or in primary care, in the first instance.

Table 2 Grading of acute asthma

Investigations in acute asthma

These should include:

• ABG if saturations <92% or with other features of life-threatening asthma
• Chest X-ray if there is any suspicion of consolidation, pneumothorax, any features of life-threatening asthma or if the patient is not responding to initial treatment

Management of acute asthma

General management includes:

• Oxygen to keep saturations 94-98%
• Corticosteroids: prednisolone 40 mg for a minimum of 5 days; ICS should be continued during this time
• Salbutamol (SABA): the nebulised route (2.5-5 mg) is preferred if there are any features of acute severe asthma; IV is reserved for those in whom inhaled routes are unreliable, e.g. with altered consciousness
• Ipratropium bromide (short-acting muscarinic antagonist): nebulised; if no response to above treatments
• IV magnesium sulphate if features of acute severe asthma are present

Intensive care referral should be considered with any of the following:

• Ventilatory support is required
• Acute severe or life-threatening asthma failing to respond to therapy, as evidenced by:
  • Investigations: deteriorating PEF, persistent or worsening hypoxia, hypercapnia, worsening acidosis
  • Clinical features: exhaustion, drowsiness, altered conscious state, respiratory arrest

Criteria for discharge

Prior to discharge, a patient should be stable off nebulisers and oxygen for 12-24 hours, have a peak flow >75% of predicted or best, and have had their inhaler technique checked.

Asthma differential diagnosis

It is important to be aware of other differentials that may present with similar symptoms to asthma, such as wheezing, cough and shortness of breath:

• COPD: consider in older patients with a strong smoking history. Typically of chronic onset, with sputum production and more frequent respiratory tract infections. Be aware of asthma-COPD-overlap syndrome, where patients may have elements of both COPD and asthma.
• Heart failure: patients can present with wheeze, cough and breathlessness; assess for evidence of fluid overload.
• Angioedema: could be secondary to an allergic reaction, hereditary angioedema or ACE-inhibitor related. Swelling in the connective tissue around the airways can cause wheeze and breathlessness.
• Eosinophilic granulomatosis with polyangiitis (EGPA): a small-medium vessel vasculitis that can commonly affect the lungs, skin and nerves, and is associated with eosinophilia and p-ANCA (usually anti-MPO antibodies). Adult-onset asthma is one of the most common signs of EGPA and it typically does not respond well to standard asthma treatment.
• Inhalation of a foreign body: typically sudden-onset wheeze and breathlessness following a history of inhaling or aspirating a foreign body.

References

• British guideline on the management of asthma. A national clinical guideline [Internet]. 2003 [cited 2022 Jan 31] Available from: https://www.brit-thoracic.org.uk/document-library/guidelines/asthma/btssign-guideline-for-the-management-of-asthma-2019/
• National Institute for Health and Care Excellence. Asthma: diagnosis, monitoring and chronic asthma management [Internet]. 2017 [cited 2022 Jan 31]  Available from: https://www.nice.org.uk/guidance/ng80/resources/asthma-diagnosis-monitoring-and-chronic-asthma-management-pdf-1837687975621
• Chapman S. Oxford handbook of respiratory medicine. Oxford, United Kingdom: Oxford University Press; 2014