Acute Asthma Flashcards
What is the definition of acute asthma?
Chronic inflammatory disease of the airways characterised by localised type 1 hypersensitive reaction and variable reversibility airway obstruction
What is the epidemiology of acute asthma?
Asthma affects 10% of children and 5% of adults
What is the aetiology of acute asthma?
- Genetic factors
- Family history - Environmental factors
- House dust mite, pollen, pets, cigarette smoke - Precipitating factors
- cold, viral infection, drugs ( beta blockers and NSAIDs), exercising, emotion
What are the risk factors for acute asthma
- Eczema
- Allergic rhinitis
- Urticaria
What is the pathophysiology of acute asthma?
- Sensitisation phase
- immune system encounters allergen and makes IgE against it
- No clinical features - Early phase
- Allergen cross-links IgE on surface of mast cells
- Causes localised degranulation an release of histamine which mediates airway obstruction via stimulation of mucus hyper-secretion, bronchoconstriction and airway oedema - Late phase
- Inflammatory cell infiltrates (lymphocytes, basophils and eosinophils) perpetuate airway obstruction and lead to bronchial hyper-responsiveness
What is the presentation of acute asthma?
General and chronic symptoms:
- Cough
- Dyspnoea
- Wheeze
- Chest tightness
- Symptoms precipitated by allergen exposure, cold air, exercise, emotion
- Diurnal variation in symptom severity
- PMH and/or FH of atrophy
- Reduced peak expiratory flow rate
- Improvement with treatment
What is the classification of asthma severity?
- Moderate
- Acute severe
- Life-threatening
- Near-fatal
What are the features of moderate asthma?
Moderate
- Increasing symptoms
- PEF > 50-75% best or predicted
- No features of acute severe asthma
What are the features of acute severe asthma?
Any one of:
- PEF 33-50% best or predicted
- Respiratory rate ≥ 25/min
- Heart rate >110 min
- Inability to complete sentences in one breath
What are the features of life threatening asthma?
Any one of the following in a patient with severe asthma:
- Clinical signs:
- Altered conscious level
- Exhaustion
- Arrhythmia
- Hypotension
- Cyanosis
- Silent chest
- Poor respiratory effort - Measurements
- PEF < 33% best or predicted
- SpO2 < 92%
- PaO2 < 8 kPa
- “normal” PaCO2 (4.6-6.0 kPa)
What is the main feature of near-fatal asthma?
Raised PaCO2 and/or requiring mechanical ventilation with raised inflation pressures.
What are the differential diagnosis of acute asthma?
- Acute exacerbation of chronic obstructive pulmonary disease (COPD)
- Anaphylaxis
- Foreign body inhalation
- Croup (children only)
- Epiglotitis
- Laryngospasm
How is acute asthma investigated?
- Peak flow (PEFR)
- Arterial blood gas (ABG)
- Full blood count
- Urea & electrolytes
- Chest radiography (CXR): Look particularly for pneumothoraces
What is the initial management of acute asthma?
- Assess the patient from and ABCDE perspective and determine severity of attack
- Obtain senior help and inform care unit (ICU) early if any features of life threatening asthma are present.
What is the ABCDE management of acute asthma??
- Airway
- Sit patient upright
- Use manoeuvres, adjuncts, supraglottic or definitive airways as indicated and suction any sputum or secretions - Breathing
- Attach monitoring:
* Pulse oximetry
* Non-invasive blood pressure
* Three-lead cardiac monitoring
- Oxygen 15L/min via reservoir mask and titrate to achieve SpO2 94-98%
- Salbutamol 5mg nebulised via oxygen-driven nebuliser (NB can give salbutamol “back to back” if severe. This means running 5mg ampoules through the nebuliser one after another. you can do this up to 5 times in a row. it takes approximately 6 minutes for one ampoule to go through so this takes approx 30 minutes 5x6)
- Ipratropium bromide 0.5 mg via oxygen driver nebuliser
This can be put in the same nebuliser as salbutamol. there is no need to give this more than once - it should only be given max QDS.
- Obtain IV access and take bloods including venous blood gas (VBG) in case ABG unsuccessful
- Performa ABG sampling:
- Markers of severity:
1. Low pH
2. PaCO2 >4.6 kPa
3. PaO2 <8 kPa - request 12 lead ECG
- A CXR is essentially always indicated in a hospitalised asthma patient, definitely if:
- A suspected pneumothorax or consolidation
- failure to respond to initial therapy
- Life-threatening asthma
- Requirement for ventilation
- Prednisolone 40 mg orally (PO) or hydrocortisone 100 mg IV is unable to swallow
- Prednisolone is a better option if possible as has a smoother profile so avoids rebound bronchospasm a few hours after treatment
- Hydrocortisone is given as a stat 100mg followed by 50mg QDS if unable to take prednisolone or concerns reabsorption of po meds.
- Magnesium sulphate 1.2-2.0g IV over 20 minutes in life-threatening or near-fatal asthma or in acute severe asthma with an inadequate response to initial therapy
- Consider aminophylline 5mg/kg IV dose over 20 minutes followed by 0.5 mg/kg/h IV maintenance dose in life-threatening or near-fatal asthma with an inadequate response to initial therapy
- Consider antibiotics if concern about bacterial precipitant of asthma attack.
