Peak Flow Meter

Introduction

Most peak flow meters are small mechanical devices with a measuring gauge, although electronic peak flow devices are also available.

• The peak expiratory flow (PEF) is the maximal rate that a person can exhale during a short maximal expiratory effort after a full inspiration.

Technique for Performing PEF Measurements

Directions for Use

• Reset the peak flow meter indicator to zero.
• Sit or stand up straight.
• Take in a deep breath, as deep as you can.
• Place peak flow meter in your mouth horizontally and close your lips tightly around the mouthpiece. Do not put your tongue against or inside the hole.
• Blow out as hard and fast as you can using your chest and belly muscles.
• Write down the result.
• Breathe normally and repeat 2 more times (3 in total).
• Record the highest of the 3 values, not the average.

Determining Personal Best PEF

Normal peak flow rate depend on a person's age, height, sex and race.

• Diurnal variation with slightly lower PEF values in the morning than in the afternoon-evening are common.

For purposes of asthma monitoring, patients should establish a personal best, rather than using an estimated PEF.

• Ideally, baseline values should be obtained from 2-4 times daily measurements over 2 weeks, when the patient is feeling well after a period of maximal asthma therapy (e.g. optimal medication use, control of triggers).
• Each patient's personal best value must be reevaluated annually for growth in children and disease progression in both children and adults.
• PEF peaks at about 18 to 20 years, maintains this level up to about 30 years in males and about 40 years in females, and then declines with age.

Asthma Self-Management

PEF monitoring can be incorporated into an asthma action plan, enabling patients to make self-management decisions based on perceived symptoms and PEF values.

A zone scheme, similar to a traffic light system, is often used.

• Green (80-100% of personal best) indicates "all clear".
• Continue current prescribed management.
• Yellow (50-80% of personal best) indicates "caution".
• Implement the treatment plan developed with the clinician to reverse airway narrowing and regain control.
• Red (below 50% of personal best) indicates "warning" or "medical alert".
• Initiate bronchodilator therapy immediately and seek immediate healthcare.

Summary

Although PEF provides an objective measurement of airway obstruction, randomized trials have not demonstrated that PEF monitoring improves outcomes compared to symptom-based diaries.

• Moreover, adherence to long-term PEF monitoring is difficult to maintain.