# Peak Flow Calculator

Determines the predicted maximum speed of expiration based on age, gender and height and compares it to the measured PEFR.

The peak flow calculator determines the PEFR (peak expiratory flow rate), which is the maximum speed of expiration of a person.

With the help of this calculator the estimated value (based on subject age, gender and height) can be compared to that obtained via physical measurement with a peak flow meter.

Peak expiratory flow is estimated via one of the three formulas, depending on whether the patient is a child, adult female or male.

Children PEFR = ((Height in cm - 100) x 5) + 100

Adult Men = (((Height in m x 5.48) + 1.58) - (Age x 0.041)) x 60

Adult Women = (((Height in m x 3.72) + 2.24) - (Age x 0.03)) x 60

Gender
Age
Height
Measured peak flow (L/min)
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Steps on how to print your input & results:

2. Then you can click on the Print button to open a PDF in a separate window with the inputs and results. You can further save the PDF or print it.

Please note that once you have closed the PDF you need to click on the Calculate button before you try opening it again, otherwise the input and/or results may not appear in the pdf.

## Variables and formula

The above calculator estimates the (predicted) peak expiratory flow based on the patient’s age, gender and height:

■ Age – the PEFR has a specific estimation formula for pediatric patients;

■ Gender – women tend to have a lower PEFR than men;

■ Height – tall individuals tend to have a higher PERF. The calculator allows input in either cm or inches, however, inches are transformed in cm that are used in the formula.

Peak expiratory flow rate (PEFR) is estimated via one of these equations:

Children PEFR = ((Height in cm - 100) x 5) + 100

Adult Men = (((Height in m x 5.48) + 1.58) - (Age x 0.041)) x 60

Adult Women = (((Height in m x 3.72) + 2.24) - (Age x 0.03)) x 60

If a measured peak flow value is available, the estimated one is compared to that and a percentage is extracted. This reflects the difference between the predicted (normal for age, gender and height) and the real value.

## PEFR explained

The peak expiratory flow rate offers information about the airflow through the bronchi, thus can quantify how severe the degree of airway obstruction is.

In order to interpret the result, a comparison is done between the measured values and the predicted ones, usually in practice these are taken from reference value tables published in literature:

■ The Wright scale;

■ EU scale;

■ NHANESIII.

Abnormally low values require immediate consult to determine lung functionality, the severity of symptoms and possible treatment.

Patients found with airway constriction are likely to necessitate further treatment for asthma and regular monitoring, as PEFR quantifies asthma exacerbation severity. However, this is not considered a diagnosis test for asthma.

According to the American Lung Association, peak flow readings are classifiable in three zones:

 Zone PEF measured from normal PEF Indication Green 80 – 100% Almost normal function, if patient has asthma, this is under control Yellow 50 – 79% Narrowed respiratory airways Red <50% Severe airway narrowing, considered medical emergency

## References

1. Balasubramanian S, Ravikumar NR, Chakkarapani E, Shivbalan SO. Peak expiratory flow rate in children--a ready reckoner. Indian Pediatr. 2002; 39(1):104-6.

2. Knudson RJ, Lebowitz MD, Holberg CJ, Burrows B. Changes in the normal maximal expiratory flow-volume curve with growth and aging. Am Rev Respir Dis. 1983; 127(6):725-34.

3. Radeos MS, Camargo CA Jr. Predicted peak expiratory flow: differences across formulae in the literature. Am J Emerg Med. 2004; 22(7):516-21.

4. Knudson RJ, Lebowitz MD, Holberg CJ, Burrows B. Changes in the normal maximal expiratory flow-volume curve with growth and aging. Am Rev Respir Dis. 1983; 127(6):725-34.

Specialty: Pulmonology

System: Respiratory

Objective: Determination

Type: Calculator

No. Of Variables: 4

Abbreviation: PEFR

Article By: Denise Nedea

Published On: June 24, 2017

Last Checked: June 24, 2017

Next Review: June 24, 2023