Asthma

• Asthma is a chronic inflammatory airway disease leading to variable airway obstruction
• Asthma


  The smooth muscle in the airways is hypersensitive and responds to stimuli by constricting and causing airflow obstruction
• Bronchoconstriction


  The bronchoconstriction in asthma is reversible with bronchodilators, such as inhaled salbutamol
• Atopic conditions


  • Eczema
  • Hay fever
  • Food allergies
• Patients with one atopic condition are more likely to have others, and these conditions characteristically run in families
• Asthma typically presents in childhood but can occur at any age
• Adult-onset asthma refers to asthma presenting in adulthood
• Occupational asthma is caused by environmental triggers in the workplace
• The severity of asthma symptoms varies greatly between individuals
• Acute asthma exacerbations involve rapidly worsening symptoms and can quickly become life-threatening
• Presentation of asthma


  Symptoms are episodic with diurnal variability, typically worse at night. Typical symptoms include shortness of breath, chest tightness, dry cough, and wheeze. Symptoms should improve with bronchodilators. No response to bronchodilators reduces the likelihood of asthma. Patients may have a history of other atopic conditions and a family history of asthma or atopy
• Examination in asthma


  • Generally normal when the patient is well. A key finding is a widespread “polyphonic” expiratory wheeze. A localised monophonic wheeze is not asthma, and the top differentials are an inhaled foreign body, tumour, or a mucus plug obstructing an airway. A chest x-ray is the next step
• Typical triggers of asthma symptoms

  • Infection
  • Nighttime or early morning
  • Exercise
  • Animals
  • Cold, damp or dusty air
  • Strong emotions
• Potential triggers of asthma symptoms

  • Infection
  • Nighttime or early morning
  • Exercise
  • Animals
  • Cold, damp or dusty air
  • Strong emotions
• Beta-blockers, particularly non-selective beta-blockers (e.g., propranolol), and non-steroidal anti-inflammatory drugs (e.g., ibuprofen or naproxen), can worsen asthma
• Spirometry


  Test used to establish objective measures of lung function by different breathing exercises into a machine that measures volumes of air and flow rates and produces a report
• FEV1:FVC ratio less than 70%


  Suggests obstructive pathology (e.g., asthma or COPD)
• Reversibility testing


  Involves giving a bronchodilator (e.g., salbutamol) before repeating 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
• Fractional exhaled nitric oxide (FeNO) testing

  Measures the concentration of nitric oxide exhaled by the patient, a marker of airway inflammation
• NICE says a level above 40 ppb in FeNO testing is a positive test result, supporting a diagnosis. Smoking can lower the FeNO, making the results unreliable
• Peak flow variability measurement

  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

  Inhaled histamine or methacholine is used to stimulate bronchoconstriction, reducing the FEV1 in patients with asthma
• NICE says a PC20 of 8 mg/ml or less in direct bronchial challenge testing is a positive test result
• NICE guidelines (2020) recommend initial investigations in patients with suspected asthma: FeNO, Spirometry with bronchodilator reversibility. Peak flow variability is the next step in diagnostic uncertainty, followed by direct bronchial challenge test with histamine or methacholine if needed
• BTS/SIGN guidelines (revised 2019) categorise patients into high, intermediate, or low probability of asthma based on clinical features and investigation results before making a diagnosis
• GINA guidelines (2022) suggest that FeNO testing is not useful in making or excluding a diagnosis of asthma
• Beta-2 adrenergic receptor agonists

  • Bronchodilators that open the airways
• Adrenalin


  • Acts on the smooth muscle of the airways to cause relaxation
• Short-acting beta-2 agonists (SABA)


  • Work quickly, used as reliever or rescue medication during acute worsening of asthma symptoms
• Long-acting beta-2 agonists (LABA)


  • Slower to act but last longer
• Inhaled corticosteroids (ICS)


  • Reduce inflammation and reactivity of the airways, used as maintenance or preventer medications
• Long-acting muscarinic antagonists (LAMA)

  • Work by blocking acetylcholine receptors to reverse bronchoconstriction
• Acetylcholine receptors stimulation


  Stimulated by the parasympathetic nervous system and cause contraction of the bronchial smooth muscles
• Leukotriene receptor antagonists action

  Work by blocking the effects of leukotrienes produced by the immune system, which cause inflammation, bronchoconstriction, and mucus secretion in the airways
• Theophylline action


  Works by relaxing the bronchial smooth muscle and reducing inflammation. It has a narrow therapeutic window and can be toxic in excess, so monitoring plasma theophylline levels is required
• Maintenance and reliever therapy (MART)


  Involves a combination inhaler containing an inhaled corticosteroid and a fast and long-acting beta-agonist (e.g., formoterol). This single inhaler is used regularly as a preventer and also as a reliever when symptoms occur
• Long-Term Management principles


  Start at the most appropriate step for the severity of the symptoms, review at regular intervals, add additional treatments as required, aim to achieve no symptoms or exacerbations on the lowest dose and number of treatments, always check inhaler technique and adherence when reviewing medications
• BTS/SIGN guidelines on asthma (2019) steps

  • Short-acting beta-2 agonist inhaler (e.g., salbutamol) as required
  • Inhaled corticosteroid (low dose) taken regularly
  • Long-acting beta-2 agonists (e.g., salmeterol) or maintenance and reliever therapy (MART)
  • Increase the inhaled corticosteroid or add a leukotriene receptor antagonist (e.g., montelukast)
  • Specialist management (e.g., oral corticosteroids)