Session 7: Asthma Flashcards
Define asthma
Chronic inflammatory disorder of the airways.
What are the 5 defining characteristics of asthma?
Chronic inflammatory process
Susceptibility
Variable airflow obstruction
Airway hyper-responsiveness
Reversibility
How does the airway obstruction in asthma differ to COPD?
In asthma it is often reversible with bronchodilators.
This is generally not the case in COPD
Explain the pathophysiology of asthma.
Macrophages process and present antigens to T lymphocytes. This will activate T cells with Th2 ells being preferentially activated.
The Th2 cells will release cytokines. This attract and activate inflammatory cells like mast cells and eosinophils.
The Th2 will also activate B cells which produce IgE.
What are the two phases of an asthmatic reaction?
Immediate response
Late phase response
Explain the immediate response (Type 1 hypersensitivity).
An example of type 1 hypersensitivity. Interaction of allergen and specific IgE antibodies lead to mast cells degranulation and release of mediators like histamine, tryptase, prostaglandin D2 and leukotrienes. This leads to bronchoconstriction.
This response is immediate and reaching maximum in about 20 minutes.
Explain the late phase response.
An example of type IV hypersensitivity. It involves inflammatory cells including eosinophils, mast cells, lymphocytes and neutrphils. They release mediators and cytokines that cause airway inflammation.
The eosinophils release leukotriene C4 and other mediators. Some of those are toxic to epithelial cells and causes shedding of them.
Explain how airway inflammation causes reduced airway calibre.
Mucosal swelling oedema (vascular leak)
Thickening of bronchial walls (infiltration by inflammatory cells)
Overproduction of mucous leading to mucus plugs.
Smooth muscle contraction
Shedding of epithelium leading to thicker mucus.
Explain hyper responsiveness of airways caused by asthma.
The inflammation causes hyper-responsiveness meaning that non-allergic stimuli like cold air and fumes can also trigger an attack.
What are the effects of narrowing airways?
Wheezing
Obstructive pattern on spirometry
Air trapping with increased residual volume.
Explain the effects on gas exchange due to asthma.
Airway narrowing leads to a reduced ventilation of the affected alveoli and therefore a V/Q mismatch.
This leads to hyperventilation but that is not enough to correct the hypoxia but will compensate for elevated levels of pCO2.
pO2 and pCO2 levels in mild to moderate asthma.
Low pCO2 and low pO2 (Type 1)
pO2 and pCO2 levels in severe attacks of asthma.
high pCO2 and low pO2 (Type 2)
This is due to extensive involvment of the airway and this leads to exhaustion. This limits the amount of CO2 that can be breathed out and leads to a rise in CO2.
Give examples of asthma triggers.
Allergens like pollen, animals.
Cold air
Exercise
Fumes
Cigarette smoke
Perfumes
Chemicals
Drugs like NSAIDs and beta blockers
Emotional distress
Treatment of asthma.
Remove triggers
Patient education
Bronchodilators (bronchodilation) and steroids (to combat inflammation)
Why are steroids inhaled and not taken orally?
Because that makes them act much more locally and not systematically in the whole body.
How does asthma present?
Dry cough which is worse at night.
Wheezing
Breathlessness
Chest tightness
What is atopy?
Triad of asthma, eczema and hayfever.
What would you examine in suspection of asthma?
Respiratory rate
Pulse
O2 sat
Bilateral wheeze
Atopy like eczema
Investigations of asthma
Peak flow chart
Spirometry to check for obstructive pattern
21 y old female with known history of asthma is admitted with acute shortness of breath and a wheeze. She is unable to speak in full sentences.
From a brief history you manage to elicit that she started to feel chest tightness when she was playing hockey.
Examinations show O2 sat at 93%, RR is 25, HR is 115.
Bilateral wheeze
ABG shows:
pH: 7.48
pCO2: 3.4 kPa
HCO3: 24 mmol/l
pO2: 9.2 kPa
What does the ABG result show?
Uncompensated respiratory alkalosis
What is the most likely diagnosis?
Acute severe asthma
Repeated ABGs show
pH: 7.41
pCO2: 5.2
HCO3: 24
pO2: 8.1
How should this be managed?
Should you be concerned?
Yes
O2
Short acting Beta 2 agonists like salbutamol
Steroids
Give examples of medication for treating asthma.
B2 agonist (e.g. salbutamol) (Short-acting or long-acting)
Anti-muscarinic
Steroid like prednisolone or hydrocortisone
