A peak flow meter for a patient with asthma is like a thermometer for a patient with a fever. Peak flow meters help to determine how open your airways are, rather than guessing just how you “feel.” In some cases when you are not feeling well, you may feel “hot” or “feverish” but when you take your temperature with a thermometer, it is normal. With asthma, sometimes you may feel your breathing is “tight” or your chest may feel “heavy” but you are having normal lung function. The peak flow meter can help you determine whether your sense of chest tightness is really an airway change or not, just like the thermometer helps you to determine if your hot feeling is really a fever.
Patients can benefit from using a peak flow meter in several ways: to recognize that asthma may be occurring at night, to improve perception of asthma, to identify factors that worsen asthma, and to predict worsening of asthma.
What Is a Peak Flow Meter?
A peak flow meter is a simple, portable and inexpensive device which measures air flow, or peak expiratory flow rate (PEFR). There are several meters available which vary slightly in accuracy, durability and price. If used appropriately, a peak flow meter can be a valuable tool in your asthma management.
Peak flow meters are available over-the-counter, but should be used with the recommendation of a physician.
Use of a Peak Flow Meter
Peak flow meters can be used as a tool to:
- determine the severity of asthma;
- check the response to treatment during an acute asthma episode;
- monitor progress in treatment of chronic asthma and provide objective information for any possible adjustments in therapy;
- detect an often unrecognized worsening in lung function and thereby avoid a possible serious flare up in asthma with early intervention; and
- diagnose exercise-induced asthma.
One of the most important functions of the peak flow meter is to help the patient and doctor evaluate the severity of asthma. Falling peak flow readings before the symptoms of asthma are otherwise noticed will indicate that an adjustment is needed. This early warning sign could mean adding a medication or making other changes in the treatment plan. The earlier the warning sign and the sooner the problem is corrected, the less medication and the less time it should take to get the lungs back to normal.
Some patients with asthma have established a backup plan with their doctor so that they know what medication to add if their peak flow drops below a certain level. Although peak flow meters are not a substitute for spirometric measurements, they are very useful for these purposes.
Proper Training Is Necessary
With home peak flow monitoring, it is essential that a patient follow some important guidelines:
(1) learn from a skilled professional how to properly use the peak flow meter;
(2) learn how and when to record (on a chart) the peak flow readings; and
(3) learn what to do if the peak flow readings fall.
Parents of young children also should learn these guidelines. Patients should bring their peak flow meters to the physician's office to check the accuracy of the unit as well as to recheck the patient's proper use of the peak flow meter.
Asthma at Night
Asthma is usually worse at night, although some patients sleep through the night unaware of lower peak flow levels. When we sleep, there is a decrease in the amount of oxygen in the blood, but in asthmatics, this fall in oxygen may happen more often and last longer. The severity of the asthma at night can be monitored with a peak flow meter. You do not have to wake up at night to use the meter. Compare the morning reading with the reading the night before to determine the degree of nocturnal (nighttime) asthma. A decrease of 15% or greater from the previous night's measurement may indicate nocturnal asthma, which you can work with your doctor to correct.
Objective Measuring Tool
There are many reasons why people are not always aware of how their bodies are functioning. Some people are “too busy” to pay attention, others deny there is anything wrong and some may find problems that do not really exist.
The regular use of peak flow monitoring has been shown to help patients gain a clearer idea of how their lungs are functioning. Without objective measurements, it is not only difficult to know how the lungs are doing, but also to determine which “trigger” factors may cause lung function to worsen. To pinpoint asthma “triggers,” you can write down peak flow meter readings before and after exposure to allergens, occupational irritants, exercise, or other events that may trigger asthma.
Peak flow readings during different seasons of the year can help to identify problems that may be caused by pollens or cold, or dry air. The many benefits of properly used peak flow meters make them worth considering for any asthma patient, especially if the asthma has been difficult to manage.
Steps to Using a Peak Flow Meter
There are several steps to properly using a peak flow meter. A good peak flow reading requires a strong blowing effort. You should blow hard on the meter to get the best reading possible and repeat this attempt three times. Record the best of the three trials. All three measurements should be about the same to show that a good effort was made each time. This is especially important when parents are evaluating their child's asthma.
Likewise, it is helpful to record readings before and after using inhaled bronchodilators. Two different symbols, such as “X” and “O,” may be used to graph these readings each morning and night. A doctor can gain a great deal of information by reviewing these readings. This will also help you to gain a better awareness of your lung function.
Keeping a chart of peak flow readings, with each day recorded in a column, helps to show how the asthma is doing. Graphs for plotting peak flow readings often come with the devices and can be photocopied for regular use.
Keep in mind that there are some general guidelines to follow when using a peak flow meter. According to the Statement on Technical Standards for Peak Flow Meters, the 10 steps toward an acceptable peak expiratory flow reading include:
1. Nose clips are unnecessary;
2. Make sure the device reads zero or is at base level;
3. Stand up (unless handicapped, in which case the position should be the same for all maneuvers);
4. Take in a deep breath as far as possible;
5. Place the meter in the mouth and close the lips around the mouthpiece;
6. Blow out as hard and as fast as possible (one to two seconds);
7. Do not cough or let the tongue block the mouthpiece;
8. Write down the value obtained;
9. Repeat the process two additional times;
10. Record the highest of the three numbers obtained and record in your diary.
Peak flow meters need some care. Follow the cleaning instructions enclosed with the units to help ensure their accuracy.
Establishing Your “Personal Best” Peak Flow
Although your predicted “normal” peak flow is determined by height, age and sex, it is preferable to gauge asthma control by comparing daily peak flow recordings with your “personal best” reading. This is defined as the highest measurement you can achieve in the middle of a good day, after using your inhaled bronchodilator.
In general, peak flow objectives in children should not decrease and, in fact, should be readjusted upwardly on a yearly basis to account for growth.
Asthma Management: Traffic Light System
Once a personal best peak flow has been established, every effort must be made to maintain values within 80% of this number.
A traffic light zonal system has been established as a rough guide to aid patients in asthma management.
PEFR (Peak Expiratory Flow Rate) 80% to 100% of personal best.
All systems “GO” – you should be relatively symptom free and can maintain your current medical regimen. If you are on chronic medications and peak flow is constantly in the green zone with minimal variation, your physician may consider gradually decreasing your daily medication.
PEFR 50-80% of personal best. “CAUTION” – asthma is worsening.
A temporary increase in asthma medication is indicated. If you are on chronic medications, maintenance therapy will probably need to be increased. Contact your physician to fine-tune your therapy.
PEFR below 50% of personal best. “DANGER” – asthma control is failing.
Use your inhaled bronchodilator. If peak flows do not return to the yellow zone, contact your physician immediately, as you must employ aggressive therapy under medical direction. In any case, maintenance therapy will have to be increased.
These traffic light zones are merely broad guidelines designed to simplify asthma management. Successful control of asthma depends on a partnership between the patient and the physician. Open communication and exchange of information can be enhanced with peak flow monitoring and reporting.
Your physician can use this objective data to design and optimally adjust your asthma therapy.
Principal Health Care of Florida, Inc.,
The American Academy of Allergy and Immunology.