Asthma

Notes

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

Aetiology and Risk Factors

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)

Risk Factors

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

Pathophysiology

Watch Video

Asthma Pathophysiology

Clinical Manifestation

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

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

SpirometryTypically from age of ~5 onward can perform reproducible spirometryTypically the flow volume loop will show an obstructive picture with classical ‘scooping’ of the expiratory flow volume loop, with a FEV1 of <0.7Positive 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

Treatment

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