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How to use peak expiratory flow rate
  1. Rebecca Dobra1,
  2. Amanda Equi2
  1. 1Department of Respiratory Medicine, Royal Brompton Hospital, London, UK
  2. 2Department of Paediatrics, Watford General Hospital, Watford, UK
  1. Correspondence to Dr Rebecca Dobra, Royal Brompton Hospital, Fulham Road, London SW3 6NP, UK; rebeccadobra{at}nhs.net

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Introduction

Asthma is the most common chronic disease of children worldwide.1 The most recent National Institute for Health and Care Excellence asthma guidelines explicitly state that asthma should not be diagnosed on symptom history alone. It calls for spirometry and peak expiratory flow rate (PEFR) assessment to assist in making the diagnosis. National and international guidelines recommend PEFR monitoring to guide chronic management decisions and to stratify risk in acute exacerbations.2 3 Despite this, the use of objective measurements of airflow obstruction has not been common in paediatric care.

The aim of this article is to explore the role PEFR plays in the assessment and management of asthma and to understand its utility and limitations as an investigation.

Physiological background

PEFR is the maximum rate of flow in forced expiration starting from full inspiration. The peak flow rate usually occurs within the first 200 ms of expiration. PEFR is conventionally measured in litres per minute. Maximal airflow occurs during the effort-dependent portion of the manoeuvre; thus, PEFR not only reflects airway calibre but also muscle strength and voluntary effort.

PEFR reflects calibre of the large airways (proximal airways, with diameter >2 mm) compared with other spirometric measurements. More distal airways have a smaller diameter and no cartilaginous support. They are susceptible to mucus plugging and collapse. Asthma is now recognised to affect the small airways4 as well as the larger airways, and peak flow may not fully assess the full extent of airway obstruction in the bronchial tree.

Technical background

The most common applications of PEFR monitoring are assessment of acute asthma and home monitoring of asthma. It can also be used in the diagnosis of asthma, identification of triggers and assessing response to treatment.

PEFR is generally recorded using a simple flow gauge device. Peak flow meters are inexpensive, with simple devices costing …

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