What is the method for calculating a normal peak expiratory flow (PEF) level?

From the Guidelines

To calculate a normal peak flow level, you should use the equation ln(PEF) = 10.99 + 2.54 ln(height in cm) for preschool children, as recommended by the American Thoracic Society/European Respiratory Society statement 1. This equation is based on a study of 214 preschool children, aged 3-7 years, with a height range of 85-130 cm, and is considered a reliable method for predicting peak expiratory flow (PEF) in this age group. When using this equation, it's essential to note that:

• Height is measured in centimeters
• The natural logarithm (ln) is used to calculate the predicted PEF value
• The resulting value is in liters per second (L/s) For example, if a child is 100 cm tall, the predicted PEF value would be calculated as follows: ln(PEF) = 10.99 + 2.54 ln(100) ln(PEF) = 10.99 + 2.54 x 4.605 ln(PEF) = 10.99 + 11.71 ln(PEF) = 22.70 PEF = e^22.70 PEF ≈ 4.58 L/s It's crucial to remember that this equation is specific to preschool children and may not be applicable to other age groups or populations. In clinical practice, it's also important to consider other factors that can affect peak flow measurements, such as:
• Age and height
• Sex and ethnicity
• Respiratory health and disease status
• Technical factors, such as the type of peak flow meter used and the patient's technique.

From the Research

Calculating Normal Peak Flow Level

To calculate a normal peak flow level, several factors need to be considered, including age, sex, height, and ethnicity.

• Peak expiratory flow (PEF) is a measure of how fast a person can breathe out after a maximum inhalation, and it is an important indicator of lung function 2.
• The normal peak flow level can be estimated using a peak flow meter, which is a device that measures the rate of air flow from the lungs 3, 4.
• The results of the peak flow measurement are compared to a standard value, which is based on the individual's age, sex, height, and ethnicity 2.
• The standard value is usually expressed as a percentage of the predicted normal value, and a value of 80% or more is generally considered normal 2.
• Factors such as asthma, bronchitis, and other respiratory diseases can affect peak flow levels, and treatment with medications such as bronchodilators and corticosteroids can help improve lung function and increase peak flow levels 5, 6.

Measurement Techniques

• Peak flow measurement is typically performed using a Wright's peak flow meter, which is calibrated for heliox or air breathing 3.
• The measurement is usually taken in the morning and evening, and the best of three attempts is recorded 4.
• It is essential to follow proper measurement techniques to ensure accurate results, including standing up straight, taking a deep breath, and blowing out as hard and fast as possible into the meter 2.

Interpretation of Results

• The interpretation of peak flow results requires consideration of the individual's clinical context, including symptoms, medical history, and response to treatment 2.
• A decrease in peak flow level can indicate a worsening of lung function, while an increase can indicate improvement 3, 4.
• Peak flow measurement is an essential tool in the diagnosis and management of asthma and other respiratory diseases, and it should be used in conjunction with other diagnostic tests, such as spirometry and provocation testing 2.