Using peak flow to monitor asthma

The meter gives a peak expiratory flow reading. Results vary with body size, age, effort and the device used, so a single number is less useful than a consistent series. Your clinician can help establish your personal best when asthma is stable and define the action ranges written into your plan.

A downward trend may occur before symptoms become obvious, while an isolated low value can reflect poor technique. Peak flow supports symptom assessment; it does not replace attention to breathlessness, wheezing, chest tightness, night waking or reduced ability to do usual activities.

Set the marker to the bottom, stand or sit upright, take the deepest breath you can, seal your lips around the mouthpiece and blow once as hard and fast as possible. Repeat as directed and record the highest acceptable result, not an average. Keep your tongue clear of the opening and reset the marker between attempts.

Measure at the times agreed in your plan, using the same meter when possible. Note symptoms, reliever use and possible triggers beside the number. Clean the device according to its instructions, and bring the meter and record to reviews so technique and changes can be checked.

Follow the action range and medicine instructions written for you if readings fall below your usual level. Seek urgent clinical advice when a low reading persists, symptoms are worsening, or reliever medicine is needed more often than your plan allows.

Call emergency services for severe breathing difficulty, inability to speak comfortably, blue or grey lips, confusion, collapse, or worsening symptoms despite emergency steps in your plan. Act on severe symptoms even if the meter is unavailable or gives an apparently reassuring number.

Ask how your personal best will be established, when you should measure, which result to record, and what each action range means for your medicines. Also check whether you should measure before or after an inhaler, how to recognise a faulty meter, and whom to contact when a trend changes.