Estimated/Expected Peak Expiratory Flow (Peak Flow)

Why Use

Asthma exacerbation severity can be quantified by comparing a patient’s current peak expiratory flow rate (PEFR) to their most recent personal best value. In the absence of a known recent personal best, this calculator can be used to estimate an expected “personal best.” The difference between the predicted and actual value can therefore help the clinician determine how severe the current exacerbation is.

When to Use

Use in patients age 5-80 years with asthma.

Formula

Pearls / Pitfalls

Useful in patients who do not know their baseline peak expiratory flow rate (peak flow). Comparison of a patient’s current peak flow to a known or expected personal best is only one aspect of the evaluation of a child with an acute asthma exacerbation. Other important factors such as respiratory rate, lung auscultation, mental status, and accessory respiratory muscle use must also be considered. Height and sex have been the factors most strongly correlated with peak flow across multiple studies; however, other differences, including ethnicity and other factors may also play a role in affecting predicted values.

Critical Actions

Assessment of peak flow must not delay administration of critical treatments for acute asthma exacerbations.

Advice

Patients with much lower actual peak flow than estimated typically require further treatment of their asthma.

More Information

Interpretation: Variability Peak flow zone >80% Green 50-80% Yellow <50% Red