Peak Flow Meters: Tracking Asthma and Breathing at Home

What peak flow measures

Peak expiratory flow (PEF) is the fastest speed of air blown out, measured in litres per minute. A normal value depends on age, height and sex, and falls with age, so a chart of "normal" values is only a rough guide. What matters is your parent's own best reading when well and well-controlled. After that, today's reading is compared with their own best.

A peak flow meter is not a diagnostic test on its own. A doctor may use it with symptoms and spirometry to diagnose asthma, check variability through the day (a swing of more than about 20 per cent suggests asthma), and monitor control.

Who may need one

• Adults with asthma, especially if symptoms are variable, severe or poorly perceived.
• People whose doctor wants to see trends before changing treatment.
• People with occupational or trigger-related asthma, for patterns.
• Some people with other lung conditions, if the doctor advises.

It is less helpful if your parent cannot make a forceful blow because of weakness, dentures that will not stay in, tremor, cognitive impairment, throat disease or severe breathlessness. In those cases, effort and technique make the numbers unreliable, and the doctor may use symptoms and the oximeter instead. See asthma in older adults: what changes after 60 and COPD at home guide.

Choosing a meter

• Adult range: most adult meters read from about 60 or 100 to 800 litres per minute. A "low-range" model is made for children and some very frail adults.
• Standard scale: newer meters follow a standard so readings are comparable between devices. Older ones may differ, so keep one meter for the same person and take it to appointments.
• Easy-to-read markings, a sliding marker that is easy to reset and a comfortable mouthpiece.
• Hygiene: a washable mouthpiece or a disposable one. Never share a meter or mouthpiece.
• Durability: a robust model that survives being dropped.
• Digital meters can store readings and may be easier for people with poor eyesight; check that they are accurate and approved.

Costs vary. Replace the meter if it is damaged or if readings suddenly seem inconsistent. See calibration, batteries and replacement of home health devices.

How to take a reading, step by step

1. Set the marker at the bottom of the scale (zero). 2. Stand up straight if possible, or sit upright. Do not lean forward or slouch. 3. Hold the meter horizontally, with fingers away from the scale and marker so they do not block it. 4. Take a deep breath in, as full as comfortable. 5. Seal the lips firmly around the mouthpiece, with the tongue not blocking the opening. Dentures that fit well can stay in; loose ones may need to be removed. 6. Blow out as hard and fast as possible, in a single sharp blast, like blowing out a candle. The blow need not be long. 7. Read the number where the marker has stopped. 8. Reset the marker to zero. 9. Repeat twice more, with a short rest in between. Allow a cough or rest if needed. 10. Record the highest of the three readings, not the average. Discard a reading made while coughing or spitting into the meter.

Record the date, time, reading and whether it was before or after a reliever medicine. A nurse or physiotherapist can show the correct technique, which makes a big difference.

Finding the personal best

For about two weeks when your parent is well, ask them to measure morning and evening, before reliever medicines (unless the doctor says otherwise) and after as advised, and record the highest reading. The personal best is the highest reading achieved during that period when the asthma is well controlled. The doctor may adjust it. It is the number to which later readings are compared. Write it on the meter and on the chart.

The zones

Many asthma plans use a traffic-light system based on percentages of the personal best. These are common examples; your doctor's plan overrides them.

Green zone: about 80 to 100 per cent of personal best. Asthma is under good control. Continue usual medicines.

Yellow zone: about 50 to 80 per cent. Caution: airways are narrowing. The plan may say to use the reliever and, in some plans, to start other steps, such as increasing medicines, only if the doctor has written those steps down. Call the doctor the same day if readings stay in this zone or if symptoms increase.

Red zone: below about 50 per cent. Medical alert. Use the reliever as per the plan and call the doctor or emergency services immediately. If your parent is severely breathless, cannot speak in sentences, is exhausted, blue or drowsy, call 112.

Do not change medicines on your own unless your doctor gave a written plan telling you precisely what to do at each zone. See building a COPD action plan with your doctor for the idea of written plans, which also exist for asthma.

How often to measure

Follow the doctor's plan. Common patterns:

• When diagnosing or adjusting treatment: morning and evening for two to four weeks.
• For routine monitoring: once a day or a few times a week, or when symptoms start.
• During a flare-up: as advised, often morning and evening, and after relievers.
• Not obsessively: repeated checking creates stress. Take readings at set times.

A drop of more than about 20 per cent from the personal best, or large swings between morning and evening, is a signal to tell the doctor.

Interpreting variability

In asthma, readings are often lowest in the early morning, and improve through the day or after a reliever. A pattern of low mornings can signal poor night-time control, nocturnal triggers or reflux. Bring the chart to the doctor, who can adjust preventers. Do not make changes yourself.

Limits in older adults

• Effort dependence: readings depend on the person's strength and understanding. A tired, depressed or confused person may produce low readings without a change in airways.
• Lower values with age, and lower still with stiff chest walls, muscle weakness and spinal curvature.
• Poor correlation in COPD, where airway narrowing is fixed and peak flow may not reflect changes.
• Variable technique: coughing, a slow blow or leaking lips lowers the number.
• Over-reliance: a good reading does not exclude trouble when your parent feels worse. Symptoms and oxygen levels matter; see pulse oximeters: how they work and how to use one.

If readings do not fit the picture, recheck technique with a nurse.

Triggers and the home

Peak flow charts can reveal triggers: dust, smoke, pollen, cold air, strong smells, mould or certain times of year. If readings fall during pollution seasons or after cleaning, discuss this with the doctor, and see indoor air quality for older lungs: dust, smoke and damp, a pollution season plan for older adults and air purifiers: choosing one for an older adult's room. Some medicines, such as beta-blockers and anti-inflammatory painkillers, can worsen asthma in some people; do not stop any medicine on your own, but tell the doctor if breathing worsens after a change.

Care of the meter

• Wash the mouthpiece in warm soapy water weekly, rinse and dry; follow the maker's instructions for the meter body. Do not boil unless the manual says so.
• Store it in a clean, dry place, away from dust and heat.
• Do not share the meter.
• Replace the mouthpiece or meter if damaged.

When to ask a professional

Ask the doctor to confirm that peak flow monitoring suits your parent, to show correct technique, to set the personal best and to write a plan for each zone. Ask the pharmacist to check inhaler technique; see inhaler technique and spacers for older adults. Call the doctor if readings fall into the yellow zone, if the reliever is needed more than usual, or if night symptoms increase. Call 112 for severe breathlessness, blue lips, confusion, exhaustion, chest pain or readings in the red zone with distress.