How can I differentiate between a mild and severe asthma attack in a patient presenting to the clinic?

To differentiate between a mild and severe asthma attack in a patient presenting to the clinic, assess the following clinical features and measurements:

• Speech and consciousness: Mild attacks allow the patient to talk in full sentences without distress, whereas severe attacks involve inability to complete sentences in one breath and may include drowsiness or confusion indicating hypoxia.
• Respiratory rate: Mild attacks have a respiratory rate less than 25 breaths per minute in adults; severe attacks have a respiratory rate over 25 breaths per minute in adults, and higher thresholds apply for children depending on age.
• Pulse rate: Mild attacks have pulse rates less than 110 beats per minute in adults; severe attacks have pulse rates over 110 beats per minute in adults, with higher thresholds for children.
• Oxygen saturation: Mild attacks maintain oxygen saturation on air at 92% or above; severe attacks show oxygen saturation less than 92% on air.
• Use of accessory muscles: Mild attacks do not involve accessory muscle use; severe attacks show use of accessory neck muscles.
• Peak expiratory flow (PEF): Mild attacks have PEF greater than 50% of best or predicted; severe attacks have PEF between 33% and 50% of best or predicted; life-threatening attacks have PEF less than 33%.
• Other signs: Severe attacks may present with exhaustion, cyanosis, silent chest (absent wheeze due to severe obstruction), or poor respiratory effort.

In summary, mild asthma attacks are characterised by stable vital signs, ability to speak normally, no accessory muscle use, normal oxygen saturation, and PEF >50% predicted or best. Severe attacks show marked respiratory distress, tachypnoea, tachycardia, hypoxia, accessory muscle use, reduced PEF (33-50%), and inability to complete sentences ¹,².