| Mild–moderate (all of): | Severe (any of): | Life-threatening (any of): | |
| Consciousness | Alert | N/A | Drowsy or unconscious |
| Speech | Can finish a sentence in one breath | Can only speak a few words in one breath | Cannot speak |
| Posture | Can walk, sit up straight, lie flat | Unable to lie flat due to dyspnoea Sitting hunched forward | Collapsed or exhausted |
| Breathing | Respiratory distress is not severe | Paradoxical chest wall movement or Use of accessory muscles of neck or intercostal muscles or ‘tracheal tug’ during inspiration or Subcostal recession | Severe respiratory distress or Poor respiratory effort |
| Skin colour | Normal | N/A | Cyanosis |
| Respiratory rate | <25 breaths/min | ≥25 breaths/min | Bradypnoea (indicates respiratory exhaustion) |
| Heart rate | <110 beats/min | ≥110 beats/min | Cardiac arrhythmia or Bradycardia (may occur just before respiratory arrest) |
| Chest auscultation | Wheeze or Normal lung sounds
| N/A | Silent chest or Reduced air entry |
| Oxygen saturation | >94% | 90–94% | <90% or Clinical cyanosis |
| Blood gas analysis (adults, if performed) | Not indicated | Not indicated | PaO2 <60 mmHg PaCO2 >50 mmHg(a) PaCO2 within normal range despite low PaO2 pH <7.35(b) |
| FEV1 | > 50% predicted or personal best | ≤50% predicted or personal best | Spirometry not feasible |
Additional information
FEV1: forced expiratory volume in one second measured by spirometry; N/A: Not applicable – may be the same as moderate and does not determine severity category; PaCO2: partial pressure of carbon dioxide in arterial blood; PaO2: partial pressure of oxygen in arterial blood
a. The presence of hypercapnoea indicates that the patient is tiring and may need ventilatory support
b. Metabolic acidosis may occur with high-dose salbutamol and with increased work of breathing