Print Friendly, PDF & Email

Acute Asthma


Definition of acute asthma

  • Chronic inflammatory disease of the airways characterised by localised type 1 hypersensitive reaction and variable reversible airway obstruction


 Epidemiology of acute asthma

  • Asthma affects 10% of children and 5% of adults


 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
      • Non-steroidal anti-inflammatory drugs (NSAIDs)
    • Exercise
    • Emotion


 Risk factors for acute asthma

  • Eczema
  • Allergic rhinitis
  • Urticaria


 Pathophysiology of acute asthma

  • Sensitisation phase
    • Immune system encounters allergen and makes immunoglobulin E (IgE) against it
    • No clinical features occur
  • Early phase
    • Allergen cross-links IgE on surface of mast cells
    • Causes localised degranulation and release of histamine which mediates airway obstruction via stimulation of mucus hypersecretion, bronchoconstriction and airway oedema
  • Late phase
    • Inflammatory cell infiltrates (lymphocytes, basophils and eosinophils) perpetuate airway obstruction and lead to bronchial hyper-responsiveness


[youtube height=”HEIGHT” width=”WIDTH”][/youtube]

Video from Oxford Medical Videos demonstrating nebuliser and inhaler use

 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 atopy
    • Reduced peak expiratory flow rate (PEFR)
    • Improvement with treatment


 Classification of asthma severity

  • Moderate
    • Worsening symptoms
    • No features of acute severe asthma
    • PEFR >50% of best/predicted
  • Acute severe
    • Inability to complete sentences in a single breath
    • PEFR <50% of best/predicted
    • Respiratory rate (RR) >/= 25
    • Heart rate (HR) >/= 110
  • Life-threatening
    • Poor respiratory effort
    • Cyanosis
    • Silent chest
    • Hypotension
    • Arrhythmia
    • Exhaustion
    • Reduced conscious level
    • PEFR <33% of best/predicted
    • Peripheral oxygen saturations (SpO2) <92%
    • Arterial partial pressure of oxygen (PaO2) <8 kPa
    • Normal arterial partial pressure of carbon dioxide (PaCO2) = 4.6-6.0 kPa
  • Near-fatal
    • Raised PaCO2 and/or requiring positive pressure ventilation with raised inflation pressures


Differential diagnosis of acute asthma

  • Acute exacerbation of chronic obstructive pulmonary disease (COPD)
  • Anaphylaxis
  • Foreign body inhalation
  • Bronchiolitis (children only)
  • Croup (children only)
  • Epiglotitis
  • Laryngospasm


 Investigation of acute asthma

  • Peak flow (PEFR)
  • Arterial blood gas (ABG)
  • Full blood count
  • Urea & electrolytes
  • Chest radiograph (CXR): look particularly for pneumothoraces


 Initial management of acute asthma

  • Assess the patient from an ABCDE perspective and determine severity of attack (see above)
  • Obtain senior help and inform intensive care unit (ICU) early if any features of life-threatening asthma are present
  • 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 5 mg nebulised via oxygen-driven nebuliser
      • 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 row. It takes approximately 6 minutes for one ampoule to go through so this takes approx 30 minutes (5×6).
    • Ipratropium bromide 0.5 mg via oxygen-driven nebuliser
      • This can be put in the same nebuliser as salbutamol. These 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
  • Perform ABG sampling
    • Markers of severity:
      • Low pH
      • PaCO2 >4.6 kPa
      • PaO2 <8 kPa
  • Request 12 lead ECG
  • A CXR is essentially always indicated in a hospitalised asthma patient, definitely if:
    • Suspected pneumothorax or consolidation
    • Life-threatening asthma
    • Failure to respond to initial therapy
    • Requirement for ventilation
  • Prednisolone 40 mg orally (PO) or hydrocortisone 100 mg IV if 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 1.2-2.0 g 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 5 mg/kg IV loading 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


 Further management of acute asthma

  • Admission criteria
    • Life-threatening asthma
    • Near-fatal asthma
    • Acute severe asthma persisting despite initial therapy
  • Indications for ICU referral
    • Requirement for ventilation
    • Poor respiratory effort
    • Drowsiness
    • Confusion
    • Deteriorating PEFR
    • Persisting or worsening hypoxia
    • Hypercarbia
    • Acidosis
    • Coma
    • Respiratory arrest
  • Discharge criteria from emergency department
    • PEFR >75% of best/predicted 1 hour after initial therapy
    • Give prednisolone 40 mg once daily for five days
    • Check inhaler technique and ensure sufficient, in-date inhaled bronchodilator
    • Arrange follow up with GP in two days


 Complications of acute asthma

  • Pneumothorax
  • Respiratory failure
  • Respiratory arrest
  • Cardiac arrest


Click here for medical student OSCE and PACES questions about acute asthma

Common acute asthma exam questions for medical students, finals, OSCEs and MRCP PACES


Click here to download free teaching notes on acute asthma: Asthma (Acute)

Perfect revision for medical students, finals, OSCEs and MRCP PACES