Respiratory Flashcards
Define viral-induced wheeze
Viral-induced wheeze = an acute wheezy illness - caused by a viral infection
Pathophysiology of viral-induced wheeze (part 1)
- 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 + oedema → swelling the walls of the airways + 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.
- This swelling + constriction of the airway caused by a virus has little noticeable effect on the larger airways of an older child or adult, however due to the small diameter of a child’s airway, the slight narrowing leads to a proportionally larger restriction in airflow.
- This is described by Poiseuille’s law, which states that flow rate is proportional to the radius of the tube to the power of four. Therefore, halving the diameter of the tube decreases flow rate by 16 fold.
Pathophysiology of viral-induced wheeze (part 2)
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.
Difference between viral-induced wheeze or asthma?
The difference 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:
* Asthma = also triggerd by viral or bacterial infections
* Other triggers: exercise, cold, weather, dust, strong emotions
* Variable + reversible airflow obstruction
Presentation of viral-induced wheeze
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.
Management of viral-induced wheeze
Managememt of viral-induced wheeze = same as asthma
Staples of management in acute viral induced wheeze or asthma are:
* Supplementary oxygen if required (i.e. oxygen saturations less than 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)
Mild:
* Salbutamol inhalers via spacer (e.g. 4-6 puffs every 4 hours)
Moderate to severe cases:
* 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
* Intubation + ventilation
Salbutamol → nebulised salbutamol/ipratropium bromide → oral prenisolone → IV hydrocorticosone
Management of viral-induced wheeze
Salbutamol → nebulised salbutamol/ipratropium bromide → oral prenisolone → IV hydrocorticosone
Define asthma
Asthma = a chronic inflammatory airway disease leading to variable airway obstruction.
* The smooth muscle in the airways = hypersensitive → responds to stimuli by constricting and causing airflow obstruction.
* This bronchoconstriction = reversible with bronchodilators such as inhaled salbutamol.
Info: Asthma being atopic
Asthma is one of a number of atopic conditions, which include:
* Asthma
* Eczema
* Hay fever
* Food allergies
Patients with one of these conditions are more likely to have others. These conditions characteristically run in families, so always ask about family history and don’t be surprised if their brother, mother or “everyone in the family” has asthma, eczema and allergies.
Presentation suggesting an asthma diagnosis
- Episodic symptoms with intermittent exacerbations
- Diurnal variability, typically worse at night and early morning
- Dry cough with wheeze and shortness of breath
- Typical triggers
- A history of other atopic conditions such as eczema, hayfever and food allergies
- Family history of asthma or atopy
- Bilateral widespread “polyphonic” wheeze heard by a healthcare professional
- Symptoms improve with bronchodilators
What is the wheeze heard in asthma?
Bilateral widespread ‘polyphonic’ wheeze
Presentation Indicating a Diagnosis Other Than Asthma
- Wheeze only related to coughs and colds → more suggestive of viral induced wheeze
- Isolated or productive cough
- Normal investigations
- No response to treatment
- Unilateral wheeze suggesting a focal lesion, inhaled foreign body or infection
Typical triggers of asthma
- Dust (house dust mites)
- Animals
- Cold air
- Exercise
- Smoke
- Food allergens (e.g. peanuts, shellfish or eggs)
Ix/diagnosis of childhood asthma
There is no gold standard test or diagnostic criteria for asthma. A diagnosis is made clinically based on a typical history and examination. Children are usually not diagnosed with asthma until they are at least 2 to 3 years old.
There are investigations that can be used where there is an intermediate probability of asthma or diagnostic doubt:
* Spirometry with reversibility testing (in children aged over 5 years)
* Direct bronchial challenge test with histamine or methacholine
* Fractional exhaled nitric oxide (FeNO)
* Peak flow variability measured by keeping a diary of peak flow measurements several times a day for 2 to 4 weeks
Long-term medical management of asthma (under 5 years old)
- Short-acting beta-2 agonist (SABA) inhaler (salbutamol) PRN
- Add low dose corticosteroid inhaler OR leukotriene agonist (i.e. oral montelukast)
- Add other option to step 2
- Refer to specialist
Long-term medical management of asthma (5-12 years old)
- Short-acting beta-2 agonist (SABA) inhaler (salbutamol) PRN
- Add low dose corticosteroid inhaler
- Add long-acting beta-2 agonist (LABA) inhaler (e.g. salmeterol)
- Titrate corticosteroid to medium dose.
- Consider adding leukotriene receptor agonist (e.g. montelukast), theophylline
- Increase soe of inhaled corticosteroid to high dose
- Referral to a specialist. They may require daily oral steroids.
SABA → beclomethasone (low) → LABA → beclomethasone (medium) → monteleukast or theophylline beclomethasone (high)
Long-term medical management of asthma (over 12 years - same as adult)
- SABA
- Low dose corticosteroid
- LABA (salmeterol)
- Titrate up corticosteroid to medium dose. Consider trial of oral leukotriene receptor antagonist (i.e. monteleukast), oral theophylline or inhaled LAMA (i.e. tiotropium)
- Titrate corticosteroid to high dose
Name a LAMA
Tiotropium
Define acute exacerbation of asthma
An acute exacerbation of asthma = characterised by a rapid deterioration in the symptoms of asthma. This could be triggered by any of the typical asthma triggers, such as infection, exercise or cold weather.
Presentation of acute asthma exacerbation in children
- Progressively worsening shortness of breath
- Signs of respiratory distress
- Fast respiratory rate (tachypnoea)
- Expiratory wheeze on auscultation heard throughout the chest
- The chest can sound “tight” on auscultation, with reduced air entry
A silent chest = an ominous sign. This is where the airways are so tight it is not possible for the child to move enough air through the airways to create a wheeze. This might be associated with reduce respiratory effort due to fatigue. A less experienced practitioner may think because there is no respiratory distress and no wheeze the child is not as unwell, however in reality this a silent chest is life threatening.
Severity of acute asthma exacerbation
Moderate:
* Peak flow > 50% predicted
* Normal speech
Severe:
* Peak flow < 50% predicted
* Saturations < 92%
* Unable to complete sentences in one breath
* Signs of respiratory distress
* Respiratory rate: > 40 in 1-5 years; > 30 in > 5 years
* Heart rate: > 140 in 1-5 years; > 125 in > 5 years
Life-threatening:
* Peak flow < 33% predicted
* Saturations < 92%
* Exhaustion and poor respiratory effort
* Hypotension
* Silent chest
* Cyanosis
* Cyanosis
* Altered consciousness/confusion
Management of acute exacerbation of asthma
Staples of management in acute viral induced wheeze or asthma are:
* Supplementary oxygen if required (i.e. oxygen saturations less than 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)
Mild:
* Salbutamol inhalers via spacer (e.g. 4-6 puffs every 4 hours)
Moderate to severe cases:
* 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
* Intubation + ventilation
Once control is established of an acute exacerbation of asthma, what do you do next?
- 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.
2 S/Es of salbutamol
- Tachycardia
- Tremor
