Asthma Flashcards
what type of hypersensitivity reaction is asthma?
type 1 hypersensitivity
what is the cascade in asthma?
genetic predisposition + trigger factor (viral, allergen, chemicals) leads to airway inflammation (mediators-histamine, leukotrienes) which leads to twitchy smooth muscle
what do intermittent attacks of bronchoconstriction cause?
- tight chest
- wheezing
- difficulty in breathing
- cough
what are the pathological changes that result from chronic asthma?
- increased mass of smooth muscle (hyperplasia and hypertrophy)
- accumulation of interstitial fluid (oedema)
- increased secretion of mucus
- epithelial damage (exposing sensory nerve endings)
- sub-epithelial fibrosis
what is the main cell that causes inflammation in asthma?
the eosinophil
why do you get the wheeze?
because once the diameter of the bronchus is infolded the airflow changes from a smooth airflow to a turbulent airflow
what happens to the FEV1 and PEFR in asthma? and why?
decrease in both FEV1 and PEFR
- Airway narrowing by inflammation and bronchoconstriction increase airway resistance
what causes bronchial hyper-responsiveness in asthma ?
epithelial damage, exposing sensory nerve endings (c-fibres, irritant receptors) contributes to increased sensitivity of the airways to bronchoconstrictor influences (and may cause neurogenic inflammation by the release of various peptides)
what happens in an immediate attack?
mainly bronchospasm but some acute inflammation - IgE mediated
what happens in the delayed phase?
inflammatory reaction
what type of hypersensitivity reaction are the early phase and late phase of asthma attack?
type 1 - early phase
type 4 - late phase
what intrinsic triggers can cause asthma?
exercise and cold
what extrinsic triggers can cause asthma?
drugs, chemicals, smoke, dust, animal dander, fungi, viral infection
what are the symptoms of asthma?
Chest tightness
Wheeze due to turbulent flow
Dry cough
Breathlessness (worse at night)
what are the signs of asthma?
episodic
diurnal variability :
a diurnal variability in PEF of more than 20% is considered diagnostic of asthma
what causes the diurnal variability?
this is because of the eosinophilic inflammation and things get activated at night
what investigations should be done?
lung function tests
- allergen skin prick test
- bronchial challenge testing (histamine and methacholine)
- exercise testing
- CO transfer
- reversibility due to inhaled salbutamol over 15%
- diurnal variation in peak flow rate
what happens to PEFR in asthma and what are the levels of severity?
decreased PEF: mod
what happens to the FEV1 and the FVC?
FEV1 decreased and FVC remains normal - obstructive pattern
what happens to gas transfer in asthma?
stays normal
what is not uncommon in spirometry?
it is not uncommon for patients whose symptoms suggestive of asthma to have normal lung function
why are methacholine/histmine/mannitol used in bronchial challenge testing?
they are markers of airwy hyper-responsiveness
- concentration to produce 20% ↓ FEV1
why are allergens/chemicals used to in bronchial challenge testing?
to diagnose occupational asthma
what pattern would be seen in exercise testing for asthma?
decreased FEV1 or PEF post exercise in asthma
what is step 1 in the treatment of asthma ?
inhaled short acting beta agonist - for mild intermittent asthma
what is step 2 in the treatment of asthma ? regular preventer therapy
add inhaled corticosteroid 200-800 microg/day
- 400 mg is an appropriate dose for many patients
what is step 3 in the treatment of asthma ?
initial add on therapy
- add inhaled LABA
- assess control of asthma
- good response to LABA - continue LABA
- benefit from LABA but control still inadequate: continue LABA and increase ICS dose to 800
- no response to LABA: stop LABA and increase ICS to 800. If still inadequate add other therapy like LTR or SR theophylline
what is step 4 in the treatment of asthma ?
persistent poor control
consider:
- increasing dose of ICS to 2000
- addition of 4th drug e.g. LTR or theophylline
what is step 5 in the treatment of asthma ?
continuous or frequent use of oral steroids
use daily steroid tablet at lowest dose providing adequate control
maintain high dose ICS
consider other treatments
what are the treatments for acute asthma (O SHIT MAn)
Oxygen (40-60%) Salbutamol (nebulised) Hydrocortisone (IV) Ipratropium (nebulised) Theophylline (oral) Magnesium sulphate (IV) Anaesthetist!
