Asthma Flashcards
What do lung function tests show in asthma?
reduced FEV1/FVC and normal FVC
FVC = Forced vital capacity - the amount of air forcefully exhaled after maximal inhalation.
FEV1 = Forced expiratory volume in 1 second - the amount of air expired in one second.
- same is shown in COPD (obstructive lung diseases)
Asthma diagnosis patients >17 years
- patients should be asked if their symptoms are better on days away from work/during holidays. If so, patients should be referred to a specialist as possible occupational asthma
- all patients should have spirometry with a bronchodilator reversibility (BDR) test
- all patients should have a FeNO test
Children 5-16 years diagnosis
- all children should havespirometry with a bronchodilator reversibility (BDR) test
- a FeNO test should be requested if there is normal spirometry or obstructive spirometry with a negative bronchodilator reversibility (BDR) test
Patients < 5 years asthma diagnosis?
diagnosis should be made on clinical judgement
FeNO
- in adults level of >= 40 parts per billion (ppb) is considered positive
- in children a level of >= 35 parts per billion (ppb) is considered positive
Spirometry
FEV1/FVC ratio less than 70% (or below the lower limit of normal if this value is available) is considered obstructive
Reversibility testing
- in adults, a positive test is indicated by animprovement in FEV1 of 12% or moreand increase in volume of 200 ml or more
- in children, a positive test is indicated by animprovement in FEV1 of 12% or more
Typical Triggers of asthma
Infection
Night time or early morning
Exercise
Animals
Cold/damp
Dust
Strong emotions
Pathophysiology of asthma?
Asthma is a chronic inflammatory condition of the airways that causes episodic exacerbations of bronchoconstriction. Bronchoconstriction is where the smooth muscles of the airways (the bronchi) contract causing a reduction in the diameter of the airways. Narrowing of the airways causes an obstruction to airflow going in and out of the lungs.
In asthma there is reversible airway obstruction that typically responds to bronchodilators such as salbutamol. This bronchoconstriction is caused by hypersensitivity of the airways and can be triggered by environmental factors.
Presentation Suggesting a Diagnosis of Asthma
Episodic symptoms
Diurnal variability. Typically worse at night.
Dry cough with wheeze and shortness of breath
A history of other atopic conditions such as eczema, hayfever and food allergies
Family history
Bilateral widespread “polyphonic” wheeze heard by a healthcare professional
Presentation Indicating a Diagnosis other than Asthma
Wheeze related to coughs and colds more suggestive of viral induced wheeze
Isolated or productive cough
Normal investigations
No response to treatment
Unilateral wheeze. This suggests a focal lesion or infection.
There are key treatments for long term management of asthma:
Short acting beta 2 adrenergic receptor agonists, for example salbutamol. These work quickly but the effect only lasts for an hour or two. Adrenalin acts on the smooth muscles of the airways to cause relaxation. This results in dilatation of the bronchioles and improves the bronchoconstriction present in asthma. They are used as “reliever” or “rescue” medication during acute exacerbations of asthma when the airways are constricting.
Inhaled corticosteroids (ICS), for example beclometasone. These reduce the inflammation and reactivity of the airways. These are used as “maintenance” or “preventer” medications and are taken regularly even when well.
Long-acting beta 2 agonists (LABA), for example salmeterol. These work in the same way as short acting beta 2 agonists but have a much longer action.
Long-acting muscarinic antagonists (LAMA), for example tiotropium. These block the acetylcholine receptors. Acetylecholine receptors are stimulated by the parasympathetic nervous system and cause contraction of the bronchial smooth muscles. Blocking these receptors leads to bronchodilation.
Leukotriene receptor antagonists, for example montelukast. Leukotrienes are produced by the immune system and cause inflammation, bronchoconstriction and mucus secretion in the airways. Leukotriene receptor antagonists work by blocking the effects of leukotrienes.
Theophylline. This works by relaxing bronchial smooth muscle and reducing inflammation. Unfortunately it has a narrow therapeutic window and can be toxic in excess so monitoring plasma theophylline levels in the blood is required. This is done 5 days after starting treatment and 3 days after each dose changes.
Maintenance and Reliever Therapy (MART). This is a combination inhaler containing a low dose inhaled corticosteroid and a fast acting LABA. This replaces all other inhalers and the patient uses this single inhaler both regularly as a “preventer” and also as a “reliever” when they have symptoms.
Confusingly the new NICE guidelines are slightly different to the SIGN/BTS guidelines. The medications they recommend are the same but they differ slightly in the stepwise ladder of which medications to introduce at what point. Most importantly they both start with a short acting beta 2 agonist followed by a low dose inhaled corticosteroid. The next step is then either a leukotriene receptor antagonist or an inhaled LABA.
BTS/SIGN Stepwise Ladder (2017 guidelines)
- Add short-acting beta 2 agonist inhaler (e.g. salbutamol) as required for infrequent wheezy episodes.
- Add a regular low dose inhaled corticosteroid.
- Add an oral leukotriene receptor antagonist (i.e. montelukast).
- Add LABA inhaler (e.g. salmeterol). Continue the LABA only if the patient has a good response.
- Consider changing to a maintenance and reliever therapy (MART) regime.
- Increase the inhaled corticosteroid to a “moderate dose”.
- Consider increasing the inhaled corticosteroid dose to “high dose” or oral theophylline or an inhaled LAMA (e.g. tiotropium).
- Refer to a specialist.
Additional Management
Each patient should have an individual asthma self-management programme
Yearly flu jab
Yearly asthma review
Advise exercise and avoid smoking
A normal pCO2 in a patient with acute severe asthma is an indicator that ?
the attack may classified be life-threatening
A normal pCO2 suggests that the patient is getting tired. Initially in acute asthma, patients are tachypnoeic and this leads to the pCO2 being low, as it is being removed from the body at a faster rate due to hyperventilation, but once patients start to tire out their respiratory muscles, it starts to increase, returning to normal. It is important that this distinction is made, as a patient with life-threatening asthma requires urgent admission to the hospital.
