PEFR

The PEFR is achieved after a tenth of a second and is measured using a peak flow meter. Peak flow meters provide a cheap method of measuring airflow obstruction and are available on prescription. A peak flow meter can be used by most adults, and by children over 6 years of age. Children under 6 years of age are not usually prescribed peak flow meters because they might confuse the blowing out for a peak flow reading with the sucking in of their inhaled medication. The patient blows into the meter as forcibly as possible and the flow of air is measured in litres per minute.

1. Diagnose asthma 2. Assess the severity or stability of asthma 3. Measure ongoing response to asthma therapies. The maximal flow rate that the patient can attain depends on: - The resistance to flow through the bronchi. - Patient effort - Patient motivation - Correct technique - Any restrictions of the chest wall. Maximal PEFR also depends on the patients’ age, gender, height and ethnic origin—a set of predicted values have been produced. Peak flow readings vary from person to person, so it is difficult to say exactly what a person’s predicted peak flow should be. It is important to ask the patient what their ‘best’ peak flow measurement has been, as this can be more meaningful than looking at predicted values alone. Patients’ should be provided with their own meter. There are several different types of meter available. Patients should be advised to bring their own meter to clinic appointments so that comparable blows are measured.

PEFR is a quick and simple test to perform. It is also easy to perform the test incorrectly. The patient should: 1. Ensure that the pointer on the meter is set at zero 2. Stand or sit in an upright position and always repeat recordings in the same position 3. Take a deep breath in to full inspiration 4. Place the lips around the mouthpiece to make a good seal 5. Hold the peak flow horizontally 6. Blow out as hard and as fast as possible (the blow should not last longer than one second) 7. Note the reading on the meter and return the pointer to zero Repeat and note the blow two more times Note down the highest of the three readings. There may be significant variability in PEFR. This is called ‘diurnal variation’. In normal health there is an increase of 5% in PEFR at midday compared with midnight. Asthma is a variable disease and this variation is small when the patient is well controlled, but there may be a difference of >10% in the morning and evening values.