Procedure

Equipment:

• Portable peak flow meter
• Disposable cardboard mouthpiece.

Protocol

1. Introduce yourself, explain the procedure, obtain consent, check the patient's identity and wash your hands.
2. Ensure the meter is reset to 'zero' by lowering the movable arrow down to the bottom.
3. The patient should ideally be standing.
4. Attach the disposable mouthpiece to the peak-flow meter.
5. Ask the patient to place the device into their mouth and enclose the mouthpiece with their lips firmly enclosed around the end, forming a tight seal. They should support the device with both hands, making sure not to obstruct the arrow.
6. The patient should inhale deeply and fully, and then exhale quickly and forcibly - it is the speed of exhalation that is being recorded. Ask the patient to, "take a deep breath and to then blow out as hard and as fast as possible, as if trying to exhale all of the air in your lungs in one go".
7. This should be repeated 3 times, allowing the patient to recover between each episode. It is the highest reading that should be recorded.
8. If the patient requires a bronchodilator (eg. Salbutamol), the peak flow measurement should be recorded both before and after it has been administrated. Document the results on the peak-flow chart.

Variations in the measurement

• General: Gender, build (mainly the height), age and disease status all affect the measurement. 
• Normal values: Use a chart for accurate values, depending on the variables above. In general, normal is 380-500L/min in women and 520-660L/min for men.
• Asthma: 'Diurnal variability' is the classic PEFR pattern in asthmatic patients (lower in the morning, highest in the middle of the day and then lowest at the end of the day).
• Asthma vs. COPD: In COPD there will be little or no reversibility (improvement of the PEFR with post-administration of a bronchodilator), but in asthma there will be a noticeable rise in PEFR.