Internal Medicine

Critical asthma syndrome (CAS)

Severe and sudden respiratory condition that, although needing aggressive and urgent treatment, has not progressed to irreversible hypoxia and cardio-pulmonary arrest.


Brittle asthma:

Asthma with dramatic fluctuations in daily PEFR despite oral corticosteroids

  • Type I: Characterized by wide swings in peak expiratory flow (PEF) despite maximal therapy.
  • Type II: Characterized by very sudden attacks.
Critical asthma syndrome (CAS) is an umbrella term that represents many other terms historically and currently used to describe acute and severe life-threatening exacerbations | Harper, R. W., & Zeki, A. A. (2015). Immunobiology of the critical asthma syndrome. Clinical Reviews in Allergy & Immunology, 48(1), 54–65.


Progression and timeline of acute exacerbation of asthma to CAS | Kenyon, N., Zeki, A. A., Albertson, T. E., & Louie, S. (2015). Definition of critical asthma syndromes. Clinical Reviews in Allergy & Immunology, 48(1), 1–6.

Clinical features

  • Sudden and rapid in onset

  • Dyspnea, paradoxical breathing, lightheadedness

  • Physical exhaustion leading to increased work of breathing

  • Failure of standard asthma therapy

  • Hypoxemia

  • Respiratory arrest

  • Death


Type I brittle asthma:

  • Oral corticosteroids or continuous subcutaneous infusion of terbutaline (or salbutamol))
  • Dietary exclusion of allergic foods

Type II brittle asthma:

Difficult to manage because they do not respond well to corticosteroids and inhaled bronchodilators.

  • Self-administered subcutaneous adrenaline (to abort the rapidly developing exacerbations)


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