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What is peak flow?
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- Asthma is a condition where the airways (bronchi), through which the air is breathed in and out of the lungs, become narrowed.
- Lung function tests applicable to asthma are used to measure the flow and volume of air moving through the airways. This information gives the doctor a picture of the status of the child’s asthma at the time of testing.
- The peak flow rate is a relatively simple function test which measures how fast the maximum amount of air can be blown out the airways. It is measured in litres per minute.
- The peak flow is obtained by the child taking a deep breath as possible (maximum inspiratory volume), and then blowing out through the peak flow meter as hard and as fast as they are able. The reading so obtained gives the highest now of air achieved during blowing out phase. By knowing the volume per second predicted for height, or better still, the individual’ s predicted maximum volume (personal best recording over a period of time), we can determine how wide the airways are at the time of testing.
Why the choice of a peak flow meter for lung function testing?
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- The peak flow meter is not that sensitive an instrument and therefore does not replace more sophisticated lung function machines. However, it is relatively cheap, portable and can easily be used to measure lung function at home, in consulting rooms and in hospitals.
- Unfortunately young children under 5-6 years old are usually not able to perform reliable peak flow readings. In these cases, a symptom diary card is used to measure the asthma status.
How do peak flow recording assist us in asthma control?
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By recording the peak flow readings together with the ffequency of bronchodilator (reliever medicines) use over a period of time, a profile of the asthma status is obtained. This is very valuable:
- in determining the therapeutic needs of a particular patient
- in assessing the efficacy of therapy and thereby making appropriate adjustments to a treatment regimen much easier
- as a diagnostic tool in suspected asthma
Remember always that the better the control of the asthma state, the less medication is needed and the less chance of being hospitalised. Both these factors greatly reduce the overall cost of management.
How to use mini peak flow meter
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General points
- Mini Peak Flow Meters are portable and easy to use
- There are a number of designs and makes available. However, instructions for one apply to all.
- When visiting your doctor, take your own peak flow meter with you. This will overcome the variation of measurements occurring in different meters. It also enables your doctor to check that your technique of usage is correct.
- If possible, recordings should be done at a time more than 4 hours after using a bronchodilator or reliever medicine
- The result is effort dependent so the greatest effort is necessary
- Blow, don’t spit into the mouth piece
- Manoeuvres like throwing the head forward to increase the score will affect the accuracy of the result
- Excess secretions in the throat will affect the reading negatively
Usage instructions
- The child must be standing when using the Mini Peak flow Meter
- Set the marker to zero
- Hold the meter parallel to the floor.
- Avoid placing fingers in the path of the marker.
- Take a deep breath, filling the lungs to their capacity.
- Place the mouth piece so that the lips firmly seal off any air loss
- Blow out as hard as possible into the mouth piece
- Read the value of the scale as shown by the marker
- Repeat twice and record the best of 3 readings
The recording of peak flow measurements
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- Use a diary card to record the morning and evening peak flow values (always the best of 3 blows)
- More frequent recordings may be done when a more complete airway status is required
- Pre- and post-bronchodilator (reliever medicine) peak flow measurements are especially valuable when there has been a deterioration of asthma state
- A note should always be made as to whether a recording has been made less than 4 hours after the last bronchodilator dose
- Most of the peak flow diary cards or booklets have a space where the frequency of bronchodilators used can be noted.
Important practical applications of the peak flow
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- Early awareness of asthma. A peak flow reading less than 80% of the predicated maximum value is an indicator of early airway narrowing (bronchospasm). This can be recorded before wheezing has developed and therefore gives you the advantage of initiating early treatment and thereby often preventing a severe relapse. This is especially important when visiting areas where medical help is not readily available.
- Signs of poor control. Frequent lower levels and wide variations in morning and evening peal now recordings (difference between morning and evening of more than 20%) suggests that a reassessment of the treatment regimen is required. These daily values will assist your doctor in deciding on these changes.
- Response to therapy. Recording peak flows before, and 10-15 minutes after the administration of a bronchodilator is an important marker in gauging the efficacy of the administered treatment. A written plan of action from the doctor should guide you in the use of the peak flow meter in this situation. It is important to remember that lung function tests may remain relatively low for some time after symptomatic recovery has occurred.
The mini peak flow meter is a vital key in the control of moderate and severe asthma.
Discuss this with your doctor.Return to top
Copyright: Allergy Society of South Africa.
Written by Dr Gerry Brereton-Stiles
Endorsed by ALLSA.ALLSA
P.O. Box 88
Observatory, 7935
Cape Town, R.S.A.
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Background: Bat Eared Fox