Box 7.2.

Levels of severity of acute asthma in adults

Level	Characteristics
Moderate asthma attacks	Increasing symptoms PEF >50%-75% best or predicted reading No features of acute severe asthma
Acute severe asthma	Any one of the following  PEF 30%-50% best or predicted reading  Respiratory rate ≥25/min  Heart rate ≥120/min Inability to complete sentences in one breath
Life-threatening asthma	Any one of the following in a patient with severe asthma  SpO2<92% (PaO2<60 mmHg) on high-flow FiO2  PEF <30% best or predicted  Bradycardia  Dysrhythmia  Cyanosis  Hypotension  Normal or high PaCO2  Exhaustion  Confusion  Silent chest  Coma Weak respiratory effort
Near-fatal asthma	Raised PaCO2 and/or requiring mechanical ventilation
Brittle asthma	Type 1: Wide PEF variability (>40% diurnal variation for >50% of the time over a period of >3-6 months) despite intense therapy Type 2: Sudden severe attacks on a background of apparently well-controlled asthma

PEF: Peak expiratory flow