Asthma Flashcards
What is the definition of asthma?
Chronic lung condition causing inflammation and hypersensitivity of the airway.
- characterised by airflow obstruction, varied over time and reversible (FEV1 by 15%)
What factors contribute to airway narrowing?
Bronchial muscle constriction - triggered by the stimuli
Mucosal swelling and inflammation
- mast cell and basophil degranulation resulting in release of inflammatory stimuli
Increased mucous production
Describe the aetiology of intrinsic asthma.
Starts in middle age (late onset)
No identifiable trigger
Describe the aetiology of extrinsic asthma.
Occurs in atopic individuals with positive skin prick test results
In non-atopic individuals, asthma develops later in life due to sensitisation
- e.g. occupational agents, aspirin, beta-blockers
- involves type 1 hypersensitivity to inhaled allergens
Describe the known pathophysiology of asthma.
Exposure to antigen causes T-cells to differentiate into Th cells and secrete IL-4 and IL-5
- IL-4 stimulates B cells to become plasma cells and secrete IgE
- IL-5 acts on eosinophils and mast cells so they react to the new antigen
IgE binds to mast cells in the mucosa and stay there until they come into contact with the antigen again
- re-exposure causes degranulation and the release of inflammatory mediators (histamine, prostaglandins and leukotrienes)
- histamine causes smooth muscle contraction, increased bronchial secretions and increased vascular permeability
Mast cells are more prevalent in the airways of asthmatics
What are the clinical features of asthma?
Intermittent dyspnoea Wheeze Cough (often nocturnal) Sputum Disturbed sleep Tachypnoea Hyperinflated chest Hyper-resonant percussive note Decreased air entry Widespread, polyphonic wheeze Diurnal variation in symptoms or peak flow
Name some common precipitants of asthma.
Cold air Emotion Allergens (house dust mite, pollen, fur) Infection Smoking Pollution NSAIDs Beta-blockers
What are the features of moderate asthma?
Increasing symptoms
PEF > 50-75% of best/predicted
no features of acute severe asthma
What are the features of acute severe asthma?
PEF> 33-50% of best/predicted
Respiratory rate >25
Heart rate >110
Inability to complete sentences in one breath
What are the features of life-threatening asthma?
PEF <33% of best/predicted Oxygen sats <92% PaO2 <8kPa Normal PaCO2 Silent chest Cyanosis Poor respiratory effort Arrythmia Exhaustion/altered consciousness level Hypotension
What are the features of near-fatal asthma?
Rasied PaCO2
Requiring mechanical ventilation with raised inflation pressures
How is the initial diagnosis of asthma made?
Clinical features of asthma
- If FEV1/FVC <0.7 then the patient gets a trial of asthma therapy (keep on lowest possible effective dose if successful)
- If FEV1/FVC >0.7 then cause is probably not asthma
How is chronic asthma monitored?
PEF monitoring - diurnal variation >20% on at least 3 days a week for 2 weeks
Spirometry
Chest X-Ray
Skin prick test to identify allergens
Histamine of metacholide challenge (indicated hyper-responsiveness)
What investigations are used in an acute asthma attack?
PEF
Sputum culture
Bloods
- FBC (increased eosinophils), U&Es, CRP and blood cultures
ABG - usually normal PaO2 and decreased PaCO2
- normal or increased PaCO2 indicates lack of respiratory effort and patient should be transferred to ITU/HDU
Chest X-Ray
What are some asthma differentials?
COPD Pulmonary oedema Large airway obstruction SVC obstruction (wheeze and dyspnoea not episodice) Pneumothorax PE Bronchitis Obliterative bronchiolotis (more likely in elderly patients)
