The peak expiratory flow rate (PEFR) is a quick and simple way to measure the severity of an asthma attack. PEFR measures the rate by which air exits the lungs. The person takes in a deep breath and blows into a spirometer, which measures the air flow in liters per minute (L/min).

The PEFR should first be measured when the person is feeling well. This value is his or her personal best PEFR. The personal best PEFR is compared to the PEFR during symptoms of asthma, in order to determine the severity of the attack. The PEFR is also used to monitor the response to treatment. Moderate asthmatics and severe asthmatics should be familiar with the PEFR zones.

PEFR Zones:

• Green Zone: a PEFR that is 80-100% of personal best represents good control
• Yellow Zone: a PEFR that is 50-80% of personal best represents a moderate attack
• Red Zone: a PEFR that is less than 50% of personal best represents a severe attack and may identify the need for treatment in an emergency department

The PEFR zone helps identify the best treatment for an acute attack of asthma.