Levels of severity of acute asthma exacerbations
| FEV1, forced expiratory volume in 1 s; Pao2, Paco2, arterial oxygen and carbon dioxide tension; Spo2, oxygen saturation. | |
| Modified from table 4 in the British Guideline on the Management of Asthma.3 | |
| Moderate asthma exacerbation | Increasing symptoms |
| FEV1 >50% best or predicted | |
| No features of acute severe asthma | |
| Acute severe asthma | Any one of: |
| FEV1 30–50% best or predicted | |
| Respiratory rate ⩾25/min | |
| Heart rate ⩾110/min | |
| Inability to complete sentences in one breath | |
| Life-threatening asthma | Any one of the following in a patient with severe asthma: |
| FEV1 <30% best or predicted | |
| Spo2 <92% | |
| Pao2 <8 kPa (60 mm Hg) | |
| Paco2 ⩾6 kPa (45 mm Hg) | |
| Silent chest | |
| Cyanosis | |
| Feeble respiratory effort, exhaustion | |
| Confusion or coma | |
| Hypotension or bradycardia | |
| Near fatal asthma | Raised Paco2 and/or requiring mechanical ventilation with raised inflation pressures |