Peak flow testing

Why does the patient’s/client’s peak flow need to be tested?

Peak flow measurements are very important in monitoring the progress of people with diseases of the lung, especially asthma. The main problem for people with asthma tends to be that their airways narrow (constrict) not when air is being breathed in (inhaled), but when it’s being breathed out (exhaled). This can lead to air being trapped in the lungs and congestion in the airways. Using a peak flow meter allows us to measure the flow rate of air as it’s being blown out by the patient/client, which tells us whether they’re having problems expelling air from their lungs.

When should I check it?

Most people with asthma will have been taught how to carry out their own peak flow testing and will have their own routine, usually involving testing first thing in the morning and last thing at night. The frequency will also vary according to the person’s general health state – a chest infection in a person with asthma can cause a real deterioration in their lung function, so peak flow testing may have to be stepped up until the person’s conditions stabilises. The times to check the peak flow will be set out in the patient’s/client’s care plan.

How do I check it?

Have a look at our animation on how to take a peak flow measurement.

What do my findings mean?

A decreasing volume of air (measured in litres per minute) being breathed out could indicate a deterioration in the patient’s/client’s condition. A normal peak flow will vary according to height, age and gender. Adults should achieve readings of 400 to 700 litres per minute, with men generally higher. Readings tend to be lower in the morning and will be affected by how recently the person has taken his or her inhaler to expand the airways.

We tend to look for trends in peak flow readings rather than sudden and dramatic changes between readings, although they can happen. You should report any reading you think is unusually low (or high) to the registered person in charge. A drop of around 20 percent from the normal would be cause for concern, but a drop of 50 percent would be alarming and would require immediate medical attention.

It’s important that you know how to manage a person who is having an asthma attack – there is good advice on this on the Asthma UK website.

Where should I record and report my findings?

Most people with asthma will take three separate peak flow readings over a few minutes and record the best score. Many have their own ‘log books’ in which they will record their scores; if a person in your care has his or her own log book and is having peak flow measurements taken, you should make sure the scores are recorded in the log book as well as in your organisation’s own observation chart. You should make sure you record your findings clearly and accurately so that they can be readily seen and understood. Always follow your organisation’s policies and procedures on recording and reporting.

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