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Table 2 Clinical and functional assessment of severe asthma exacerbations

From: Clinical review: Severe asthma

Variable Severe exacerbation Imminent respiratory arrest
   Dyspnea At rest  
   Speech Single words, not sentences of phrases  
   Alertness Agitated Drowsy or confused
   Respiratory rate >30 breaths/min  
   Heart rate >120 beats/min Bradycardia
   Pulsus paradoxus >25 mmHg Absence (muscle fatigue)
   Use of accessory muscles Evident Abdominal paradox
   Wheeze Present – loud 'Silent chest'
Functional assessment   
   PEF <50% of predicted  
   PaO2 <60 mmHg  
   PaCO2 >42 mmHg  
   SaO2 <90%  
  1. PaCO2, arterial carbon dioxide; PaO2, arterial oxygen; PEF, peak expiratory flow; SaO2, oxygen saturation. Adapted from the National Heart, Lung and Blood Institute report [1].