What is peak expiratory flow (PEF)?

From the Guidelines

Peak expiratory flow (PEF) is a crucial measurement for monitoring asthma control, and patients should use a peak flow meter to track their PEF regularly, ideally at the same time each day, to detect early signs of asthma exacerbation. PEF is a measurement of how quickly a person can exhale air from their lungs at maximum effort after taking a deep breath, typically measured in liters per minute (L/min) using a small handheld device called a peak flow meter 1. According to the guidelines, PEF is primarily used to monitor asthma and other respiratory conditions by tracking changes in airway function over time, and a significant drop in PEF (typically 20% or more below the patient's personal best) may indicate worsening asthma control and the need for medication adjustment.

Key Points to Consider

• PEF monitoring can help detect early signs of asthma exacerbation before more severe symptoms develop, allowing for timely intervention 1.
• Factors affecting PEF include age, height, gender, and ethnicity, so personal best values are more useful for monitoring than population-based predicted values.
• The available data suggest symptom monitoring and peak flow monitoring have similar benefits in determining asthma control, and long-term, daily peak flow monitoring can be useful, particularly in patients with moderate- to severe-persistent asthma 1.
• A final recommended determinant of current impairment is forced expiratory volume in one second (FEV) or peak expiratory flow (PEF) rate, with 80 percent or more of predicted or personal best categorizing patients’ asthma as well controlled, and less than 60 percent of predicted or personal best indicating very poor control 1.

Recommendations for PEF Monitoring

• Patients with asthma should measure their PEF regularly, ideally at the same time each day, and record these values in a diary or chart.
• Patients should be taught how to use a peak flow meter and how to act on the results, including when to increase treatment, call their doctor, or readmit themselves to hospital 1.
• A written self-management plan should be provided to all patients, including guidelines on PEF monitoring and action plans for worsening asthma control.

From the FDA Drug Label

Published reports of trials in asthmatic children aged 3 years or older have demonstrated significant improvement in either FEV1 or PEFR within 2 to 20 minutes following a single dose of albuterol inhalation solution

• Peak Expiratory Flow (PEF) is also referred to as PEFR in the drug label.
• The drug label does not provide a direct definition of PEF, but it is mentioned as a measure of pulmonary function that is improved by albuterol inhalation solution, similar to FEV1.
• Based on the context, it can be inferred that PEF or PEFR refers to the maximum rate of airflow during a forced exhalation, but this is not explicitly stated in the label 2.

From the Research

Definition of Peak Expiratory Flow (PEF)

• Peak expiratory flow (PEF) is defined as the maximum flow at the mouth achieved during an expiration, delivered with maximum force starting from the level of maximum lung inflation 3
• PEF measures the speed at which air is forcefully exhaled from full inspiration, expressed in litres per minute (L/min) 4

Measurement of PEF

• PEF is obtained when the expiration is initiated with maximal inflation of the lungs, because this will make the elastic recoil pressure maximal and the upstream frictional pressure loss minimal 3
• PEF is obtained with maximum expiratory effort, because high acceleration of flow will cause wave speed limitation at a higher lung volume 3
• The position of the head should be neutral, because hyperextension may increase PEF and flexion may decrease PEF by changing the stiffness of the larger airways 3

Clinical Significance of PEF

• PEF is an important test in the diagnosis and monitoring of respiratory conditions, especially asthma 4
• PEF is an objective measure of airflow obstruction that patients can learn with little difficulty, and which provides physicians objective information for assessing a patient's condition 5
• PEF monitoring is used in the management of patients with asthma, and can be used to assess the effectiveness of treatment 6, 7

Factors Affecting PEF

• The best PEF may be the better index for the management of patients with asthma, as it can provide a more accurate assessment of pulmonary function than the predicted PEF 6
• The ratio of the best PEF to the predicted PEF can vary significantly between patients, and using the predicted PEF as the index may result in underestimation or overestimation of pulmonary function in some patients 6