What peak flow measurement indicates a patient is in the red zone of an asthma action plan?

A peak flow measurement that indicates a patient is in the red zone of an asthma action plan is less than 50% of their personal best. This zone signals a severe reduction in airflow and suggests that the patient may be experiencing significant asthma symptoms, necessitating immediate medical intervention and possibly the use of rescue medication. The red zone is critical because it indicates that the patient's asthma is poorly controlled, and they are at high risk for an exacerbation or an asthma attack.

In the context of an asthma action plan, understanding these zones is vital for patient self-management. Those in the red zone require patients to take urgent steps to manage their condition, such as using bronchodilators and seeking medical assistance. This knowledge empowers patients to recognize when their condition is deteriorating and take appropriate action to prevent further complications.