assessment of severe asthma in adults

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Management of acute asthma in adults

Assessment of severe asthma

  • Healthcare professionals must be aware that patients with severe asthma and one or more adverse psychosocial factors are at risk of death.

Moderate Acute asthma:

  • increasing symptoms
  • PEF > 50-75% best or predicted
  • no features of acute severe asthma

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

Life-threatening asthma:

  • In a patient with severe asthma any one of:
    • PEF < 33% best or predicted
    • SpO2 < 92%
    • PaO2 < 8 kPa
    • 'normal' PaCO2 (4.6-6.0 kPa)
    • altered conscious level
    • exhaustion
    • arrhythmia
    • hypotension
    • cyanosis
    • silent chest
    • poor respiratory effort

Near-fatal asthma:

  • Raised PaCO2 and/or requiring mechanical ventilation with raised inflation pressures

Initial assessment of symptoms, signs and measurements

Clinical features

  • severe breathlessness (including too breathless to complete sentences in one breath), tachypnoea, tachycardia, silent chest, cyanosis or collapse
    • none of these singly or together is specific and their absence does not exclude a severe attack

  • PEF or FEV1
      • PEF or FEV1 are useful and valid measures of airway calibre.
      • PEF expressed as a % of the patient's previous best value is most useful clinically. In the absence of this, PEF as a % of predicted is a rough guide
  • Pulse oximetry
    • Oxygen saturation (SpO2) measured by pulse oximetry determines the adequacy of oxygen therapy and the need for arterial blood gas (ABG) measurement. The aim of oxygen therapy is to maintain SpO2 94-98%

  • Blood gases (ABG)
    • Patients with SpO2 <92% or other features of life-threatening asthma require ABG measurement

  • Chest X-ray
    • Chest X-ray is not routinely recommended in patients in the absence of:
      • suspected pneumomediastinum or pneumothorax
      • suspected consolidation
      • life-threatening asthma
      • failure to respond to treatment satisfactorily
      • requirement for ventilation


  • SIGN (July 2019). British Guideline on the management of asthma (SIGN158)

Last edited 01/2020