Peak Expiratory Flow Rates (PEF Charts)

Suggested Reference Peak Expiratory Flow (PEF) Values for Children

Peak Expiratory Flow in Normal Adult Subjects

Calculating % Predicted Peak Flow Rate

Calculating Peak Flow Variability

SUGGESTED REFERENCE PEAK EXPIRATORY FLOW (PEF) VALUES FOR CHILDREN:

PEAK EXPIRATORY FLOW IN NORMAL ADULT SUBJECTSAdapted with kind permission from Nunn AJ Gregg I, Br Med J 1989:298;1068-70 and Clement Clarke International.

CALCULATING % PREDICTED PEAK FLOW RATE

• Take the best of 3 of the patient’s observed peak flow rate:
  e.g. 200, 180, 190 performed – so take 200
• Find the patient’s sex, age and height predicted value from nomogram or table:
  e.g. 440 for a woman of age 25 years and height 167 cm
• Divide patient’s observed peak flow rate over their predicted peak flow rate:
  e.g. 200/440 = 0.45
• Multiply by 100:
  e.g. 0.45X100 = 45%

So, in this example, the patient’s observed peak flow rate is 45% of predicted.

CALCULATING PEAK FLOW VARIABILITY

There are a number of methods for calculating PEF variability.

One method is described below:

• Subtract the lowest from the highest reading
• Divide by the highest reading
• Multiply by 100

So, in this example, where a patient has readings of 300 to 400, the variability is 25%. If these readings were taken before and after a test dose of salbutamol, asthma is diagnosed. (See Chronic asthma)

Standard Treatment Guidelines and Essential Medicines List for South Africa, Primary Healthcare Level, 2020 Edition