Asthma Flashcards
What is asthma?
Chronic inflammation of airways and hyper responsiveness which causes narrowing of airways
Causes of asthma
Genetic factors (family history)
Environmental factors
Triggering substance of asthma
- air pollution: cigarette smoke, car fumes
- allergens: dust, animals, mould, pollen
- medication: aspirin (NSAIDs), beta blockers
- cold air
Symptoms of asthma
- dry cough (often at night)
- chest tightness
- dyspnoea
- wheezing/high pitched whistling on exhalation on
Why is a dry cough in asthma more common at night?
Increased vagal activity at night
What investigations can be used to diagnose asthma?
- Peak flow + diary
- Spirometry (<70%) + reversibility testing
- FeNO
- direct bronchial challenge test
What is bronchial challenge test?
- patient breathes in powder that irritates airways
- patient’s breathing is tested after each dose to see how much the airways narrow
- dose is increased until breathing ability drops by <20% or max dose is reached
diagnosis of asthma
- spirometry with bronchodilator reversibility: <70% + improvement of >12% with bronchodilators
- FeNO: >40ppb
Outline the fractional exhaled nitric oxide test for investigation of asthma
What result would support diagnosis?
Why could it be unreliable?
- measures the conc. of NO exhaled (marker for airway inflammation)
- steady exhale for around 10s into device
- > 40ppb is a positive test
- smoking lowers FeNO so could be unreliable in smokers
Management of asthma
- education
- up to date vaccinations
- avoid triggers
- drug treatment: bronchodilators + steroids
- inhalers
Stepwise approach of medications in chronic asthma
Only move onto next step if current step isn’t working:
- SABA e.g. salbutamol, terbutaline PRN
.
- ICS e.g. beclomethasone
- LABA e..g salmeterol, formoterol
- higher dose ICS, leukotriene receptor antagonists
- referral to specialist care
Difference in NICE + BTS guidelines for asthma management
- low dose ICS first for both
- NICE: add LTRA
- BTS: add LABA
New asthma medication guidelines
- first line: AIR therapy: low dose ICS + formoterol combination PRN
- second line: low dose MART
- third line: moderate dose MART
- if still uncontrolled and good adherence + technique: check FeNO level + eosinophil
- if not raised: trial addition of LTRA or LAMA for 8-12 weeks
- if still uncontrolled: refer to specialist
New asthma guidelines in children 5-11 years old
**
What is AIR therapy + MART?
- AIR: anti-inflammatory reliever - PRN
- MART: maintenance and reliever therapy - everyday + during an attack
- use of ICS/formoterol therapy
Why have the asthma management guidelines changed?
risks of SABA overuse
How do you grade asthma exacerbation severity?
mild:
- no features of severe asthma
- PEFR >75% of best or predicted
moderate:
- no features of severe asthma
- PEFR 50-75%
severe: (any one of)
- PEFR 33-50%
- cannot complete sentences in 1 breath
- RR >25
- HR >110
life threatening: (any one of)
- PEFR <33%
- sats <92% or ABG pO2 <8kPa
- cyanosis, poor resp effort or near/fully silent chest
- exhaustion, confusion, hypotension or arrhythmias
near fatal:
- all of above but raised pCO2
How do you manage an acute asthma exacerbation?
- oxygen (aim for 94-98%)
- 2.5-5mg nebulised salbutamol (repeat after 15mina if needed)
-
40mg oral prednisolone
. - if severe, 500mg nebulised ipratropium bromide
. - if life threatening or near fatal:
- urgent ITU, portable CXR + anaesthetist assessment
- IV aminophylline
- consider IV salbutamol if nebulised route ineffective
What class of drug is aminophylline + what is its mechanism of action?
Methylxanthine class
- it inhibits phosphodiesterase > increased cAMP in smooth muscle cells > bronchodilation
- also has anti-inflammatory effects
What does the term controlled oxygen refer to?
Who typically needs it?
- the administration of O2 at specific conc. or flow rate to achieve a target O2 saturation
- key in patients with COPD (risk of CO2 retention)
Key aspects: - precise control of O2 delivery
- monitoring O2 sats
- prevention of complications e.g. hypercapnia
Criteria for safe asthma discharge post exacerbation
- PEFR >75%
- stop regular nebulisers 24hrs prior to discharge
- reassess inhaler technique + adherence
- written asthma action plan
- at least 5 days oral prednisolone
- GP follow up within 2 days
- resp clinic follow up within 4 weeks
What is an asthma management plan?
A written document designed for each individual with asthma to help control their symptoms + reduce exacerbations
Components:
- daily treatment instructions
- monitoring + symptoms tracking e..g peak flow diary
- action plan for exacerbations
Blue vs brown inhalers
Blue: bronchodilator acts a reliever (short term)
Brown: anti inflammatory (corticosteroids) to reduce risks of asthma attacks (longer term)
Describe how asthma attacks happen and what process take place in the body
- triggered by something in th environment
- picked up by dendritic cells
- present to type 2 helper cells - CD4+
- cytokines releases (IL-4+IL5)
- IL-4: production of IgE antibodies > coat mast cells and stimulate the release of histamines, leukotrienes + prostaglandins
- IL-5: act on eosinophils > release more cytokines + leukotrienes
- causes smooth muscle spasm + increased mucous secretion
- also increased vascular permeability > immune cells from blood > eosinophils damage endothelium of lung
- airways become even narrower
What immune cells are in involved asthma?
Type 2 helper cells
B cells > plasma cells > antibodies
What is the atopic triad?
Asthma
Atopic dermatitis
Allergic rhinitis
What type of reaction do IgE antibodies cause?
Type 1 hypersensitivity
What cytokines are released in asthma?
IL-4
IL-5
What does the release of IL-4 cause?
- production of IgE antibodies (type 1 hypersensitivity reaction)
- IgE coat mast cells
- histamines, leukotrienes + prostaglandins are released
What does the release of IL-5 cause?
- act on eosinophils
- release leukotrienes + more cytokines
What does chronic asthma cause?
Airways remodelling - irreversible changes
- hypertrophy + hyperplasia of smooth muscle
- hypertrophy of mucous glands
- thickening of basement membrane
What three processes affect the airways in an asthma attack?
- smooth muscle spasm
- increased mucous secretion
- increased vascular permeability > immune cells from blood > eosinophils damage endothelium of lung
Makes airways even narrower
What is asthma characterised by?
A triad of:
- bronchial smooth muscle contraction
- airways inflammation
- increased secretions
What are the two phases of immune response in asthma?
Immediate response: type 1 hypersensitivity (IgE) > bronchial smooth muscle contraction
Late phase response: type IV hypersensitivity (eosinophils) > airways inflammation
Outline the immediate response to asthma triggers
- type 1 hypersensitivity
- production of IgE antibodies
- coat mast cells
- histamine, prostaglandins + leukotrienes released
- causes bronchoconstriciton
Outline the late phase response in asthma triggers
- type IV hypersensitivity
- includes inflammatory cells e.g. eosinophils, mast cells, lymphocytes, neutrophils
- release leukotrienes + cytokines
- causes airway inflammation
What features of airway inflammation cause reduced airflow?
- mucosal swelling (oedema)
- thickening of bronchial walls
- mucous over production
- smooth muscle contraction
-
epithelium is shed + incorporated into thick mucous
. - triggers airway hyper-responsiveness
What are the effects of airway narrowing on gas exchange?
reduced ventilation > V/Q mismatch
How can asthma cause type 1 respiratory failure?
- in unmanaged mild asthma
- airways narrowing > reduced ventilation
- hyperventilation can’t compensate for hypoxaemia but can compensate for CO2 retention
- low pCO2 + low pO2
How can asthma cause type 2 respiratory failure?
- in severe attacks
- complete blockage of some airways + exhaustion which limits amount of CO2 which can be breathed out
- this leads to a rise in CO2 in body
- high pCO2 + low PO2
Why might a normal pCO2 level on ABG be concerning in a patient having a acute asthma exacerbation?
- initially the patient is hypocapnic
- the asthma attack continues + severity of airflow obstruction increases
- the hypocapnia becomes normocapnia before becoming hyercapnia
- normocapnia is a step in the progression from type 1 respiratory failure to type 2
Describe airway hyperresponsiveness
- inflammation makes airway more ‘reactive’ to triggers
- triggers can cause bronchoconstriction
What type of countries is asthma more prevalent in?
High income countries
Describe an asthmatic’s airway when they are well/symptom free
Inflamed + thickened walls
Describe an asthmatic’s airway during an attack
- inflamed + thickened wall
- increased mucous
- tightening smooth muscle
- air trapped in alveoli
What is atropy?
Genetic tendency to develop allergic diseases
Inhaler types
- pressued metered dose inhalers - aerosol
- dry powder inhalers
- soft mist inhalers
