Asthma

Overview

Overview Asthma is a chronic airway inflammation disorder due to complex interactions between inflammatory cells, mediators and airway cells. In young children in whom lung function testing is not feasible, including most preschool children, asthma is defined by the presence of variable respiratory symptoms. Asthma is one of the most common causes of presentation to the Emergency department It implies reversible airway constriction (peak flows vary by >20%) +/- wheeze, dyspnoea or cough

Definition
Asthma: Condition of bronchial hyperactivity and smooth muscle hypertrophy leading to a chronic inflammatory condition of the airways associated with widespread bronchospasm that is reversible.
Acute cough: Condition for less than 3 weeks, most commonly caused by acute upper respiratory infection but also may be caused by congestive heart failure, pneumonia, and pulmonary embolism.
Chronic cough: Condition for longer than 3 to 8 weeks (case definitions vary). Smoker - chronic obstructive pulmonary disease. Nonsmoker with a normal chest radiograph and not taking an ACE inhibitor, it may be due to postnasal drip, gastroesophageal reflux disease (GERD), or asthma.

Airway obstruction occurs due to a combination of:

  • Inflammatory cell infiltration
  • Mucus hypersecretion with mucus plug formation
  • Smooth muscle contraction

This page will mainly focus on paediatric asthma

Epidemiology

  • Paediatric asthma is the most common chronic respiratory disease in the developed world, with the highest prevalence found in English-speaking countries such as the US, the UK, and Australia.
  • Good control of asthma and prevention of exacerbations is important.
  • There is a variable gender effect, with a higher prevalence in prepubertal males and postpubertal females
  • Between 30-80% of children become asymptomatic around the time of puberty.

Patterns of Asthma

Infrequent intermittent asthma (70-75% of cases)

  • Episodes of asthma lasting days to a week
  • Episodes are generally 6 or more weeks apart
  • Asthma triggered my URTI
  • No need for preventer

Frequent intermittent asthma (20-25% of cases)

  • Episodes occur at intervals less than 6 weeks
  • Minimal symptoms between episodes
  • Children may benefit from regular preventative therapy usually with ICS or Leukotriene antagonist

Persistent asthma (5-10% of cases)

  • Symptoms on most days including:
    • Disruption of sleep due to wheeze and cough
    • Early morning dyspnoea
    • Exercise dyspnoea or activity intolerance
  • Require preventive therapy
  • Referral to a paediatrician

Anatomy of the Respiratory Tract

Risk Factors

  • Allergic sensitisation
  • Atopy
  • Family History
  • Passive or Active tobacoo smoker
  • Viral infections
  • Higher serum eosinophils

Signs and Symptoms

Asthma Triad CDE: Cough, Dyspnea, Expiratory wheeze

Parental anxiety should not be discounted: it is often of significance even if the child appears relatively well.

Certain thing can trigger a wheezing episode in asthma

  • Pollen
  • Dust
  • Featheres
  • Fur
  • Excercise,
  • Viruses
  • Chemical
  • Smoke
  • Traffic

Differential Diagnosis

  • Foreign Body
  • Pertussis
  • Croup
  • Pneumonia/TB (Do X-Ray!)
  • Aspiration
  • Cystic Fibrosis
  • Transient infant wheezing
  • Sinusitis
  • Cardiac failure due to congenital heart disease
  • Structural airway abnormality - laryngomalacia, vascular ring

Investigations

  • FBC
  • Chest X-ray
  • Arterial/Venous blood gas (for severe asthma)
  • Spirometry
Side note Spirometry
  • Typically from age of ~5 onward can perform reproducible spirometry
  • Typically the flow volume loop will show an obstructive picture with classical ‘scooping’ of the expiratory flow volume loop, with a FEV1 of <0.7
  • Positive bronchodilator response: an FEV1 of 12% or 200mL 10-15min following administration of a -agonist

Diagnosis

  • Clinical History
  • Clinical features cough, dyspnoea and wheeze
  • Clinical Response to bronchodilator

Aetiology and Pathophysiology

Aetiology

  • Genetic predisposition
  • Triggers
    • Infections à viral (up to 80% of hospital admissions for asthma are following a viral illness)
    • Exercise (especially in dry, cold air)
    • Allergens (dust mites, pollen, food, animal dander)
    • Environment smoking
    • Chemicals (salicylates)

Pathophysiology

Pathophysiology

Watch Asthma Pathophysiology

Management

Asthma action plan

The essential elements of asthma self-management education are:

  • Written information about asthma and individualised patient details
  • Self-monitoring of symptoms and/or lung function (spirometry, peak flow)
  • A written asthma action plan
  • Regular review by doctor, asthma educator, or nurse on medications and current asthma control, reinforcement of trigger avoidance behaviours and lifestyle changes if warranted, feedback to the patient about how well they are controlling their asthma, and how control can be improved
Screen Shot 2016-10-13 at 11.39.36 AM

Image from Australian Asthma Handbook

MEDICATIONS FOR CHILDHOOD ASTHMA
Medication Mechanism of Action Contraindication Side-effects
Short Acting b2-agonist Sympathomimetic relaxes bronchial smooth muscles by stimulating B2 receptors Tremors, palpitations, headache. Hyperglycaemia, tachycardia, muscle cramps, lactic acidosis, hypokalaemia
Long Acting b2-agonist Sympathomimetic relaxes bronchial smooth muscles by stimulating B2 receptors Tremors, palpitations, headache. Hyperglycaemia, tachycardia, muscle cramps, lactic acidosis, hypokalaemia
Ipratropium bromide Anticholinergic M3 receptor antagonist – promote bronchodilatation by inhibiting parasympathetic bronchomotor tone Dry mouth, throat irritation, blurred vision, dizziness, urinary retention, constipation
Theophilines
(aminophylline)		 Not understood – thought to have adrenergic effects as well as anti-inflammatory effects Nausea, vomiting, diarrhoea, GOR, anxiety, tremor, palpitations, seizures, arrhythmias, tachycardia
Corticosteroids Reduce airway inflammation and bronchial hyper-reactivity Candidiasis, bruising, facial skin irritation due to nebules, systemic effects (adrenal suppression, bone density loss, glaucoma, skin thinning and bruising, impaired growth)
Magnesium
Adrenaline

 

Asthma Emergency

Assessment of and management of Asthma in Emergency

  • Acute Mild/moderate asthma
  • Acute asthma
  • Life-threathening asthma

References

Australian Asthma handbook 2015
Contents
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