Viral Induced Wheeze

Question 1

What is viral induced wheeze?

Cause?

Answer 1

Viral-induced wheeze describes is an acute wheezy illness caused by a viral infection. Small children (typically under 3 years) have small airways. When these small airways encounter a virus (commonly RSV or rhinovirus) they develop a small amount of inflammation and oedema, swelling the walls of the airways and restricting the space for air to flow. This inflammation also triggers the smooth muscles of the airways to constrict, further narrowing the space in the airway.

Air flowing through these narrow airways causes a wheeze, and the restricted ventilation leads to respiratory distress. For some reason, certain children are much more prone to this airway swelling than others. There seems to be a hereditary element, so when assessing a wheezy child ask about a family history of viral-induced wheeze. These children are at higher risk of developing asthma in later life.

Question 2

How to distinguish between viral-induced wheeze and asthma?

Answer 2

The distinction between a viral-induced wheeze and asthma is not definitive. Generally, typical features of viral-induced wheeze (as opposed to asthma) are:

Presenting before 3 years of age
No atopic history
Only occurs during viral infections

Asthma can also be triggered by viral or bacterial infections, however it also has other triggers, such as exercise, cold weather, dust and strong emotions. Asthma is historically a clinical diagnosis, and the diagnosis is based on the presence of typical signs and symptoms along with reversible airflow obstruction.

Question 3

Presentation of viral-induced wheeze?

Answer 3

Evidence of a viral illness (fever, cough and coryzal symptoms) for 1-2 days preceding the onset of:

Shortness of breath
Signs of respiratory distress
Expiratory wheeze throughout the chest

TOM TIP: Neither viral-induced wheeze or asthma cause a focal wheeze. If you hear a focal wheeze be very cautious and investigate further for a focal airway obstruction such as an inhaled foreign body or tumour. These patients will require an urgent senior review.

Question 4

Management of viral-induced wheeze?

Answer 4

Management of viral-induced wheeze is the same as acute asthma in children.

Staples of management in acute viral induced wheeze or asthma are:

Supplementary oxygen if required (i.e. oxygen sats <94% or working hard)
Bronchodilators (e.g. salbutamol, ipratropium and magnesium sulphate)
Steroids to reduce airway inflammation: prednisone (orally) or hydrocortisone (intravenous)
Antibiotics only if a bacterial cause is suspected (e.g. amoxicillin or erythromycin)

Bronchodilators are stepped up as required:

Inhaled or nebulised salbutamol (a beta-2 agonist)
Inhaled or nebulised ipratropium bromide (an anti-muscarinic)
IV magnesium sulphate
IV aminophylline

Mild cases can be managed as an outpatient with regular salbutamol inhalers via a spacer (e.g. 4-6 puffs every 4 hours).

Moderate to severe cases require a stepwise approach working upwards until control is achieved:

Salbutamol inhalers via a spacer device: starting with 10 puffs every 2 hours
Nebulisers with salbutamol / ipratropium bromide
Oral prednisone (e.g. 1mg per kg of body weight once a day for 3 days)
IV hydrocortisone
IV magnesium sulphate
IV salbutamol
IV aminophylline

If you haven’t got control by this point the situation is very serious. Call an anaesthetist and the intensive care unit. They may need intubation and ventilation.

Once control is established: you can gradually work your way back down the ladder as they get better:

Review the child prior to the next dose of their bronchodilator.
Look for evidence of cyanosis (central or peripheral), tracheal tug, subcostal recessions, hypoxia, tachypnoea or wheeze on auscultation.
If they look well, consider stepping down the number and frequency of the intervention.
A typical step down regime of inhaled salbutamol is 10 puffs 2 hourly then 10 puffs 4 hourly then 6 puffs 4 hourly then 4 puffs 6 hourly.

Consider monitoring the serum potassium when on high doses of salbutamol as it causes potassium to be absorbed from the blood into the cells.

It is also worth noting that salbutamol causes tachycardia and a tremor.