How to use a peak flow meter

A peak flow meter (or, rarely, a small electronic portable spirometer) is sometimes recommended as part of a treatment plan. These handheld devices measure how fast a person can blow air out of the lungs. Asthma causes patients to not be able to blow air out fast because their airways are narrowed, so a low measurement with this device suggests problems are occurring with your child’s asthma. These measurements can help warn a patient or parent that extra medication is needed to fend off more severe asthma symptoms. The results can also be useful for the patient who does not adequately perceive worsening airway obstruction or who has difficulty distinguishing anxiety or hyperventilation attacks from asthma. When your child is having asthma problems, a peak flow reading puts a number on how she is doing, much as a thermometer shows how high a temperature is. Your pediatrician or asthma specialist will show you how to record your child’s baseline measurements at a time when she is doing well with her asthma. This is referred to as her “personal best.” When your child’s asthma is not doing well or is at risk of flaring up (eg, during a “cold”), a peak flow reading can be obtained and the value compared to the child’s personal best. Using a simple range of color zones—green, yellow, and red, like traffic lights—specific recommendations can be spelled out as to what needs to be done to prevent a full-blown asthma attack based on what color zone the patient falls into with her peak flow measurement.

How to Use a Peak Flow Meter

Your child’s peak flow–based asthma treatment plan uses his own personal best peak flow reading because every child is unique. Your child’s peak flow may be higher or lower than that of another child even though their age, sex, and height are identical.

To find your child’s personal best, your pediatrician will instruct him to use the peak flow meter at the same time every day for 2 to 3 weeks during a period when he doesn’t have any symptoms and asthma is under good control.

To obtain a peak flow measurement, have your child do the following:

  1. Stand up.
  2. Place the peak flow device indicator at 0.
  3. Take a deep breath, then place the device well in to the mouth.
  4. Close his lips around the mouthpiece and keep his tongue clear of the opening.
  5. Blow once as hard and fast as he can. Note the reading.

Repeat steps 2 through 5 twice more and write down the highest score.

After your child has established his personal best your doctor may ask him to use the meter for readings when he is beginning to have symptoms, or when he has a “cold” (a time when asthma commonly gets worse). The doctor may also ask you to monitor his peak flow when adjustments have been made to his medication program, whether it be up or down, to detect any change in asthma control.

Starting at about age 4 or 5 years, your child can learn how to use a peak flow meter. The following color zone system is commonly used with peak flow monitoring:

  • Green means that the airflow score is at 80% to 100% of your child’s personal best peak flow (the targeted peak flow value determined by your child’s pediatrician); his medications don’t need to be adjusted and he may continue full activity.
  • Yellow means caution, just as it does on the road with a traffic light; airflow is between 50% and 80% of your child’s personal best and certain additional asthma medications should be started or increased to ward off symptoms.
  • Red means danger; your child’s score is less than 50% of his peak flow. Have your child take his quick-relief medications (usually a bronchodilator at a high dose to open up the airways and steroid pills or liquid to calm inflammation) if it is part of the asthma action plan worked out between you and your pediatrician or asthma specialist. Call or see your physician soon, or go for emergency care, if the peak flow reading stays below 50% despite the treatment.

The peak flow meter provides one way to measure asthma objectively, but it’s critical that the child and everyone else in the family not rely on just a peak flow number for assessment of how a child’s asthma is doing. Symptoms are as important, probably even more important, than a peak flow reading. It is not uncommon for symptoms to detect a flare-up of asthma even before peak flow measurements do.