How to keep a Peak Flow Chart

What is peak flow?

Peak expiratory flow (PEF) is a measurement of how fast you can blow air out of your lungs. It can be measured at home by a portable peak flow meter (PFM). Daily recordings of peak flow help you and your doctor to assess your asthma control better than a single reading in the doctor's surgery. When your asthma is well controlled your PEF will be higher because your airways are open. If asthma causes them to become narrower, you will find it more difficult to blow out fast and your PEF will fall.

Why do we measure peak flow?

All people with asthma need to have their lung function measured from time to time. Regular peak flow monitoring helps your doctor to assess your asthma control when you are away from the surgery and in your normal day-to-day environment at work or at home. Peak flow readings also help to assess your response to treatment. A change in PEF can help you and your doctor to identify worsening asthma and can alert you to increase your medication to prevent more severe asthma attacks. Peak flow monitoring can also be used to help the doctor to make a diagnosis of asthma.

Some people with asthma are very good judges of their lung function and asthma control. Other people are unaware of their asthma severity; and in these situations, relying on changes in symptoms can be dangerous by causing a delay in starting or increasing medication to treat an acute attack of asthma.

Who should perform peak flow measurements?

Most patients with moderate to severe asthma should record their PEF regularly. Patients with milder asthma may only need to record at times when their asthma may become unstable. Such times occur when their treatment is changed, if they have a cold, during periods of weather change or exposure to triggers which are known to cause changes in asthma. It is most important that people who have suffered a recent acute attack of asthma continue to measure until their readings have returned to normal and their asthma symptoms are stable. Monitoring also helps determine the best PEF you can achieve. Knowing this personal best PEF will enable your doctor to write an action plan to help you identify changes in your asthma and to increase your treatment according to the plan if your symptoms worsen. An action plan will help you to make decisions about your treatment at home and will indicate when you should seek emergency help.

What is a peak flow chart?

The most simple record of your peak flow can be made on any piece of paper which lists your morning and evening peak flow readings. Sometimes these are recorded by using graph paper which gives a clear picture of the changes in your peak flow readings from day to day (Figure). There are several different charts available, and your doctor will provide you with one when you start to measure your peak flow readings. You will probably be asked to measure your readings regularly morning and night. It is also sometimes useful to measure your readings after your reliever medication. You can also take your peak flow meter to work and to measure your readings when you are exposed to triggers which you suspect are causing your asthma symptoms. Your doctor may ask you to measure your peak flow after exercise to assess the severity of exercise-induced asthma and the effectiveness of your medication.

How should your peak flow measurements be recorded?

An accurate peak flow reading is dependent on a maximum effort. The PEF occurs very early when you breathe out after full deep breath, so there is no need to continue breathing out for longer than a few seconds. You should always use the same peak flow meter for all your measurements. The readings depend on how hard you blow, and it is important to blow as hard as you can.

How to measure your peak flow

• Push the pointer on the peak flow meter to zero.

• Keep the meter horizontal and keep your fingers away from the sliding scale.

• Take as big a breath as possible. Seal your lips around the mouthpiece. Blow as hard and fast as you can (pretend you are blowing a dart out of a blowpipe).

• Read where the pointer reaches and write it down.

• Do two more blows and record the highest (not the average) of these three readings on your peak flow chart.

How often should you record your peak flow reading?

Your doctor will advise you when to record your PEF. You may be asked to record your PEF 10 to 15 minutes after taking your reliever medication. People with asthma have changes in peak flow which are termed 'diurnal variation'. This is due to the natural change in your peak flow readings from the morning to later in the day. The morning peak flow is usually the lowest, and it is best to take this reading as soon as you get up.

How to record your peak flow readings

It is usual to mark your PEF recorded before medication with a dot and to mark the readings taken after medication with a cross. You may then have a series of dots which can be joined up over many days to show a pattern of your peak flow readings (Figure). A change in this pattern, especially a drop in your readings, will help to alert you to a change in your asthma and the need to increase your medication.

Your doctor may use a colour-coded chart or action plan which defines a green normal zone, an amber or yellow warning zone, and a red emergency zone for you. In addition, some peak flow meters have green, yellow and red arrows which can mark these zones on your peak flow meter. It is helpful to take your usual meter when visiting your doctor.

How to look after your peak flow meter

Most peak flow meters can be washed in warm soapy water, rinsed and left to dry. This does not need to be done any more frequently than once a month. Otherwise it is wisest to follow the cleaning instructions which come with your meter. Your PFM should last two to three years if it is used on a daily basis. Significant drops and rough handling over time can reduce the life expectancy of a PFM.

Which portable PFM should you use?

There are many peak flow meters available and your doctor will inform you of the most appropriate purchase. People with low peak flow readings, especially children and some older patients, should use a low flow PFM which has a range of zero to 300 litres per minute and which can be easily read. The standard PFM usually has a range from zero to 800 litres per minute. The mini-Wright, Allersearch, Vitalograph, Breathtaker, fDe and Personal Best, are all suitable for general use. There may be significant differences between individual peak flow meters, and this is why it is best to take your own meter with you when you visit your doctor.

Pitfalls in measuring peak flow

• Peak expiratory flow is a measure which needs maximum effort. If you don't blow as hard as you can, your reading may be low. This is why it is essential to blow as hard as you can. It is important to seal your lips tightly around the mouthpiece so that there is no leak of air as you blow out.

• Some patients may have symptoms of chest tightness and their peak flow readings don't change. This may be a result of narrowing of the small airways which the peak flow meter does not measure very well.

• If your peak flow reading is low or very variable and you are feeling well, you should check your technique with your doctor.

• It is helpful to indicate on your peak flow record if you have taken a bronchodilator (reliever) within 4 hours of your PEF reading.

  Please Note: This information is intended by The Australian Lung Foundation to be used as a guide only and is not an authoritative statement. Please consult your family doctor or specialist respiratory physician if you have further questions relating to the information provided here.

  For details of patient support groups in Australia please call 1800 654 301