Asthma action plans outline three “zones” (green, yellow, and red) based on the severity of symptoms and/or the peak expiratory flow (PEF). PEF is a lung function test that adults and older children can take at home by breathing into a simple plastic device, known as a peak flow meter. (Younger children cant easily use these devices, which require exhaling a breath as quickly and forcefully as possible into the device.)
An action plan can help you determine how severe an asthma attack is and which treatment is appropriate. Matching symptoms or PEF with the appropriate zone on the action plan will tell you which treatment to follow, whether its taking extra medication or seeking help.
To see what an asthma action plan looks like, you can download this PDF from the National Heart, Lung, and Blood Institute.