Asthma

What is Asthma?

Most common childhood disease.
Chronic inflammatory disorder of the bronchi.
Characterized by episodic, reversible bronchospasm, caused by a bronchoconstrictor response to various stimuli.
Triggers differ dependent on the person.

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The lining of the bronchioles become swollen and inflamed.
The lumen narrows due to inflammation causing airway oedema.
Bronchioles produce excess mucus to trap the antigen - this can cause mucus plugs.

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Inhaled antigen causes an immune response.
The blood vessels become leaky, allowing IgE and eosinophils to travel to the tissues.
Antigen activates dendritic cells and macrophages. These are antigen-presenting cells (APC), they present the antigen to T helper cells.
Macrophages begin to engulf and eliminate the antigen.
Th1 cells activate lymphocytes (T cells, B cells and natural killer cells). They also contribute to bronchoconstriction.
Th2 cells activate IgE cells and eosinophils. They are also needed for the proliferation and differentiation of B cells.
Eosinophils release neuropeptides which cause tissue injury and airway hyperresponsiveness.
IgE cells bind to an antigen and then bind to mast cells causing the mast cells to release histamine.
Histamine causes inflammation and contributes to bronchoconstriction.
Airway obstruction via inflammation increases airflow resistance and decreases flow rate. This can trap air.
Trapped air leads to decreased diffusion in the alveoli. This causes VQ mismatch.

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Exposure to allergens/irritants
Genetics - If a parent has asthma, the child will be more susceptible to it.
Exercise - During exercise breathing is fast and through the mouth. This causes cold, dry air to reach the lungs which can irritate the airway.
Stress - Makes inflammatory response more prominent to environmental triggers.
Recurrent Respiratory Infections -
- Recurrent infections with episodes of wheezing during early life are a risk factor for later asthma diagnosis.
- Damage to epithelial barrier causes a risk of severe infections.

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Cough - An irritant causes the bronchial tubes to constrict, prompting a non-productive cough.
Wheezing - Narrowing of the lumen and excess mucus production can cause mucus obstructions in the airway. These causing a 'wheeze' sound as air is inspired/expired.
Tachycardia - Heart rate increases to compensate for lack of oxygen being transported to the blood.
Tachypnoea - As the airway narrows, less oxygen is inspired. When CO2 levels rise, the pH of the blood drops. This sends a message to the medulla to increase the respiratory rate to get a higher level of oxygen into the body.
Shortness of Breath - The lungs can't hold as much air due to inflammation and mucus build-up.

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Respiratory Assessment - Chest observed for pattern of breathing, symmetry of movement and accessory muscle usage. A doctor will listen to chest for wheezing, stridor and air entry/exit.
Monitoring
- ECG - monitor heart rate (side effect of salbutamol is tachycardia).
- Blood gasses - monitor oxygen and carbon dioxide levels in the blood.
- Peak flow - measure how quickly air can be expelled from the lungs (indicates a narrowing of the bronchioles).
Inhaled Corticosteroids - taken daily to reverse inflammation of the airway.
Salbutamol Inhaler - taken PRN (as needed). Opens the airway during symptomatic episodes.
Oxygen - given during asthma exacerbation. Reverses hypoxia.
Magnesium Sulfate - given during asthma exacerbation. Relaxes bronchiole muscles and expands the airway.
Education - Children and parents taught correct inhaler technique and receive advice on avoiding triggers.
Follow Up - Follow up with GP who continues to monitor the patient and prescribe medications. Asthma clinic review to check symptom management.

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