MCC Paramedic Program

Peak Flow Meters


How To Use a Peak Flow Meter

A peak flow meter is a device that measures how well air moves out of the lungs.

They are primarily used with asthma patients and should not be confused with Incentive Spirometers.  During an asthma episode the bronchial tubes and bronchioles of the lungs begin to narrow.  This process can be very fast or can take hours to days.  The peak flow meter is especially useful for the gradual onsets cases because the patient will be alerted to a problem of declining airflow hours, even days, before the patient has any noticeable symptoms of asthma. By identifying and treating an attack early, one may be able to stop the episode quickly and avoid a serious episode of asthma. Peak flow meters are prescribed to almost all asthma patients age 5 and older. They are used to check asthma the way that blood pressure cuffs are used to check high blood pressure. Paramedics can also use peak flow measurement during acute episodes to determine whether the patient is moving towards improvement or is worsening.

Peak Flow meters are often “prescribed” so that insurance companies will cover the cost. The device can be purchased at most drug stores or medical supply stores without a prescription.

The peak flow meter can assist the physician with medical surveillance of the patient:

·        It helps determine if the medicine plan is working well.

·        It helps determine if medications or treatments should be started or stopped.

·        Help patients determine when to seek emergency care.

·        Identify triggers that cause asthma symptoms to increase.


The peak flow meter can assist the paramedic with medical treatments during an acute episode:


  • It helps determine if the medications are relieving bronchoconstriction
  • It can help identify “reflex broncospasm” which requires immediate cessation of aerosolized therapy.
  • It helps to triage patients to home, doctor’s office or emergency Department.
  • It provides tangible, objective assessments of airflow for research and protocol development.



How to Use a Peak Flow Meter

1. Apply a new mouth piece to the Peak Flow Meter.  Place the indicator pointer at the base of the numbered scale (usually zero).

2. Have the patient stand up if appropriate.

3. Have the patient take a very deep breath. Do not inhale through the device.

4. Place the meter in your mouth and close your lips around the mouthpiece. Keep the tongue away from the air tube. (On the outside of the device, do not block the air exit ports with your fingers! This will falsely alter the value)

5. Have the patient blow out as hard and fast as they can.

6.  Write down the value as X Liters/min. Where X is a number obtained from the meter.

7. Repeat steps 3 through 6 two more times.

8. Document  the highest of the three numbers achieved.

Maintenance Instructions for patients at home

Your personal best peak flow number is the highest peak flow number you can achieve over a 2-week period when your asthma is under good control. Good control is when you feel good and do not have any asthma symptoms.

Each patient's asthma is different and your best peak flow may be higher or lower than the average usual number for someone of your height, weight, and sex. This means that it is important for you to find your own personal best peak flow number. Your own medicine plan needs to be based on your own personal best peak flow number.

To find out your personal best peak flow number, take peak flow readings:

·        Every day for 2 weeks

·        Mornings and evenings (when you wake up and about 10-12 hours later)

·        Before and after taking inhaled beta2-agonist (if you take this medicine)

·        As instructed by your doctor

Write down these readings on a worksheet

The Peak Flow Zone System

Once you know your personal best peak flow number, your doctor will give you the numbers that tell you what to do. The peak flow numbers are put into zones that are set up like a traffic light. This will help you know what to do when your peak flow number changes. For example:


Green Zone (80 to 100 percent of your personal best number) signals all clear. No asthma symptoms are present, and you may take your medicines as usual.

Yellow Zone (50 to 80 percent of your personal best number) signals caution. You may be having an episode of asthma that requires an increase in your medicines. Or your overall asthma may not be under control, and the doctor may need to change your medicine plan.

Red Zone (below 50 percent of your personal best number) signals a medical alert. You must take an inhaled beta2-agonist right away and call your doctor or a paramedic immediately if your peak flow number does not return to the Yellow or Green Zone and stay in that zone.


Record your personal best peak flow in My Weekly Asthma Symptom and Peak Flow Diary.

Use the Diary To Keep Track of Your Peak Flow

Write down your peak flow number on the diary every day, or as instructed by your doctor.

Discuss With Your Doctor What To Do When Peak Flow Numbers Change

The most important thing about peak flow is how much it changes from your personal best number and from one reading to another.


·        A decrease in peak flow of 20 to 30 percent of your personal best may mean the start of an asthma episode.

·         If your peak flow is less that 50% of your personal best and you are having symptoms of an asthma attack, call paramedics.