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Peak Flow Meters/Oximeters/Spirometers

What is a peak flow meter?

A peak flow meter (PFM) is a device used to measure how well your child's asthma is under control. The device measures air flowing out of the lungs, called peak expiratory flow rate (PEFR), as a child with asthma forcefully blows into the device. A peak flow meter, when used properly, can reveal narrowing of the airways well in advance of an asthma attack. As part of your asthma care plan, peak flow meters can help determine:

  • When to seek emergency medical care

  • The effectiveness of your child's asthma management and treatment plan

  • When to stop or add medication, as directed by your child's doctor

  • What triggers the asthma attack, such as exercise-induced asthma

Why should a peak flow meter be used?

The PFM removes a lot of guesswork out of managing your child's asthma. It can provide you, your child's doctor, or even the school teachers with information about how open the airways are in your child's lungs.

The PFM can detect small changes in the large airways before your child starts to wheeze. Using a PFM every day will let you know when your child's peak flows are starting to drop. This allows you to make early changes in your child's medication or routine to help prevent your child's asthma symptoms from getting worse. The PFM can also identify the value at which you will need to call your child's doctor or go to the emergency room.

How do you use a peak flow meter?

Use the PFM once daily and whenever your child is experiencing early warning signs. Always use the PFM before taking reliever medication.

  1. Hold the PFM by the handle.

  2. Before each use, make sure the pointer is reset to zero.

  3. Have your child stand up straight. Remove chewing gum or any food from your child's mouth.

  4. Have your child take a deep breath and put the mouthpiece in his or her mouth. Seal his or her lips and teeth tightly around the mouthpiece.

  5. Let your child blow out as hard and as fast as he or she can. Remember a "fast blast" is better than a "slow blow."

  6. Note the number where the pointer has stopped on the scale.

  7. Reset the pointer to zero.

  8. Repeat this routine three times. You will know your child has done the technique correctly when the numbers from all three tries are close together.

  9. Record the highest of the three readings on a graph or in a notebook. Do not average these numbers together. This is called your "peak flow."

  10. Use the peak flow meter once a day. Measure peak flows about the same time each day. A good time might be when your child first wakes up or at bedtime.

What are peak flow zones?

Peak flow zones are based on the traffic light concept: red means danger, yellow means caution, and green means safe. These zones are different for each person. Your child's doctor will help determine your child's peak flow zones. The three peak flow zones include:

  • Green: This is the go zone! This zone is from 80 to 100 percent of your child's highest peak flow reading. This is the zone your child should be in every day. This is a signal that air moves well through the large airways and that your child can do the usual activities and go to sleep without trouble. When the peak flow readings are in this zone, your child should:

    • Avoid asthma triggers.

    • Use controller medications every day.

    • Use the reliever medications 15 to 20 minutes before exercise if your child has exercise-induced asthma, as directed by your child's doctor.

  • Yellow: This is the caution or slow down zone! This zone is from 50 to 80 percent of your child's highest peak flow reading. This is a clue that the large airways are starting to narrow. Your child may begin to have mild symptoms. Your child may be coughing, feeling tired, feeling short of breath, or feeling like his or her chest is tightening. These symptoms may keep your child from his or her usual activities or from sleeping well. To keep your child's peak flow numbers from getting worse and get your child's asthma back under control, you will need to:

    • Continue to use the controller medication as your child's doctor has ordered and avoid asthma triggers.

    • Use the reliever medication as ordered by your child's doctor.

    • Make sure you are using the proper technique with your child's metered-dose inhaler and spacer.

  • Red: This is the stop zone! This zone is less than 50 percent of your child's highest peak flow reading. Readings in this zone are a medical emergency and you will need to get help right away. This means severe narrowing of the large airways has occurred. Your child may now be coughing, very short of breath, wheezing both when breathing in and out, or having retractions. Your child may also have problems walking and talking. Have your child take his or her reliever medication now and call your child's doctor.

The goal of the peak flow zones is to help you recognize when the asthma may start to become uncontrolled. The goal is to stay within the 80 percent value of your personal best peak flow measurement. Zones with a smaller range, such as 90 to 100 percent, may be recommended by some health care providers. Always follow the advice of your doctor regarding the peak flow rate.

How is a personal best peak flow measured?

Each child's peak flow zones are based on his or her personal best peak flow number. To establish your child's personal best peak flow, have your child take his or her peak flow measurement each day at the same time for two to three weeks, when the asthma is under control.

After recording your child's peak flow measurements for two to three weeks consistently, your child's doctor may also measure the optimum lung function with a spirometer (a device that can check lung function by measuring both the amount of air expelled and how quickly the air was expelled). The spirometer measurement may then be compared with the peak flow meter record to help set up an asthma management and treatment plan.

Your child's personal best peak flow measurement may change over time. Consult your child's doctor as to when to check for a new personal best peak flow measurement.

When should a peak flow meter be used?

Peak flow meters should be used regularly to check how well the asthma is being controlled. In addition, the peak flow meter may be a valuable tool during an asthma attack, because it can help determine how well the short-term, quick-relief asthma medication is working. The National Heart, Lung, and Blood Institute (NHLBI) recommends measuring lung function during the following times:

  • Every morning, before taking asthma medications

  • During asthma symptoms or an asthma attack

  • After taking medication for an asthma attack

  • Other times as recommended by your child's doctor

The peak flow meter is a tool to help collect information. The key to successful asthma management is communicating this information (the peak flow meter recordings, the severity of your child's symptoms, and the effectiveness of your child's medications) to your child's doctor.

How can I obtain a peak flow meter?

Consult your child's doctor about obtaining a peak flow meter and for step-by-step instructions on how to use the device.

If you are using more than one peak flow meter, be sure they are the same brand.

What are oximeters?

An oximeter is a small machine that measures oxygen saturation (the amount of oxygen) in your child's blood.

To get this measurement, a small sensor (similar to an adhesive bandage) is taped onto your child's finger or toe. When the oximeter is on, a small red light can be seen in the sensor. The sensor is painless and the red light does not get hot.

What is a spirometer?

A spirometer is a device used by your child's doctor that assesses lung function. Spirometry, the evaluation of lung function with a spirometer, is one of the simplest, most common pulmonary function tests and may be necessary for any of the following reasons:

  • To determine how well the lungs receive, hold, and utilize air

  • To monitor a lung disease

  • To monitor the effectiveness of treatment

  • To determine the severity of a lung disease

  • To determine whether the lung disease is restrictive (decreased airflow) or obstructive (disruption of airflow)

After taking a deep breath, your child forcefully breathes out into the spirometer as completely and forcefully as possible. The spirometer measures both the amount of air expelled and how quickly the air was expelled from the lungs. The measurements are recorded by the spirometer.

The normal, healthy values measured by the spirometer for the amount of air exhaled vary from child to child. Your results are compared to the average expected in someone of the same age, height, sex, and race, according to NHLBI. However, if the values fall below 85 percent of the average, it may indicate a lung disease or other airflow obstruction. If a child has abnormal spirometer measurements, he or she may be referred for other lung tests to establish a diagnosis.

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