The peak expiratory flow (PEF), also called Peak expiratory flow
rate (PEFR).
Is a person’s maximum speed of expiration, as measured with a
peak flow meter.
it is a small hand device used to monitor a person’s ability to
breath out air.
It measures the airflow through the bronchi and thus the degree of obstruction in the airways.
Function
Peak flow readings are higher when patients are well, and lower when the
airways are constricted. From changes in recorded values, patients and
doctors may determine lung functionality, the severity of asthma symptoms, and treatment.
Measurement of PEFR requires training to correctly use a meter and the normal
used to the wide range of 'normal' values and the high degree of variability,
peak flow is not the recommended test to identify asthma. However, it can be useful in some circumstances.
A small portion of people with asthma may benefit from regular peak flow
monitoring. When monitoring is recommended, it is usually done in addition to reviewing asthma symptoms and frequency of reliever medication use.
When peak flow is being monitored regularly, the results may be recorded on a
peak flow chart.
How The Test Is Performed
Peak Expiratory Flow Rate (PEFR) is a quick and simple measurement .
A small tube with a slider device measures how fast air is driven through the tube
by the subject exhaling rapidly.
The subject takes a deep breath in, then breathes out as hard and as fast as
possible, three times and the third time the subject blows into the tube.
With a good airtight seal of the lips around the tube.
This is best done standing up; the best three attempts is usually taken, with a short
rest between attempts.
Test Results Explained
The normal range of peak flow measurements depends on the age, gender and
height.
There is a reasonable ‘Spread’ of normal values for any group of people with the
same age height and gender.
The individual’s personal best measurement is a more reliable guide to predicting
Purpose of Pulmonary Functioning Testing
The pulmonary functioning testing has been a major step forward in assessing the
functional status of the lungs as it relates to:
1. How much air volume can be moved in and out the lungs. 2. How fast the air in the lungs can be moved I and out.
3. How stiff are the lungs and the chest wall- a question about compliance.
4. The diffusion characteristics of the membrane through which the gas moves
(determined by a special tests).
Pulmonary Functioning Test are used for the
following reasons:
1. Screening for the presence of obstructive and restrictive diseases
2. Evaluating the patient prior to surgery- this is especially true to patients who:
Are older than 60-65 years of age
Are known to have pulmonary disease Are obese (as in pathological obesity)
Have a history of smoking, cough or wheezing
Note
A vital capacity is a important preoperative assessment tool.
Significant reductions in vital capacity (less than 20cc/Kg of ideal body weight) Indicates that the patient is at higher risk for postoperative respiratory
complications.
This is because vital capacity reflects the patient’s ability to take a deep
Pulmonary Functioning Test are used for
the following reasons:
3
.evaluating the patient’s condition for weaning from the ventilator. If
the patient on a ventilator can demonstrate a vital capacity (VC) of
10-15ml/Kg of body weight, it is generally thought that there is
enough ventilatory reserve to permit (try) weaning and extubation.
4. documenting the process of pulmonary disease- restrictive or
obstructive
Measurement
The highest of three readings is used as the recorded value of the Peak Expiratory
Flow Rate.
It may be plotted out on graph paper charts together with a record of symptoms
or using peak flow charting software.
This allows patients to self-monitor and pass information back to their doctor or
nurse.
Peak flow readings are often classified into 3 zones of measurement according to
the American Lung Association; green, yellow, and red.
Doctors and health practitioners can develop an asthma management plan
Zone Reading Description
Green Zone 80 to 100 percent of the usual or normal peak flow readings are clear.
A peak flow reading in the green zone indicates that the asthma is under good control.
Yellow Zone 50 to 79 percent of the usual or normal peak flow readings
Indicates caution. It may
mean respiratory airways are narrowing and additional
medication may be required.
Red Zone Less than 50 percent of the usual or normal peak flow readings
Indicates a medical emergency.
Severe airway narrowing may be occurring and
To interpret the significance of peak expiratory flow measurements, a
comparison is made to reference (normal, predicted) values based on measurements taken from the general population.
Various reference values have been published in the literature and vary by
population, ethnic group, age, sex, height and weight of the patient.
For this reason, tables or charts are used to determine the normal value for a
particular individual.
More recently, medical calculators have been developed to calculate predicted
values for peak expiratory flow.
There are a number of non-equivalent scales used in the interpretation of peak
