Background
Peak expiratory flow rate (PEFR) is the maximum flow rate (expressed in liters per minute [L/min]) generated during a forceful exhalation, starting from full inspiration. [1] PEFR primarily reflects large airway flow and depends on the lung recoil, voluntary effort, and muscular strength of the patient.
Maximal airflow occurs during the effort-dependent portion of the expiratory maneuver; thus, low values may be caused by a less than maximal effort rather than by airway obstruction. However, PEFR is variable among individuals with a similar body build; such variation has to do with airway size versus lung size. Nevertheless, the ease of measuring PEFR with an inexpensive small portable device has made it popular as a means of following the degree of airway obstruction in patients with asthma and other pulmonary conditions.
Forced expiratory volume over 1 second (FEV1) is a dynamic measure of flow used in formal spirometry. It represents a truer indication of airway obstruction than does PEFR. Although PEFR usually correlates well with FEV1, this correlation decreases in patients with asthma as airflow diminishes. [2]
PEFR monitoring can be accurately performed by most patients older than 5 years. It is most commonly measured by a portable flow gauge device (peak flow meter [PFM]) but may also be obtained by a transducer that converts flow to electric output during spirometry (pneumotachometer). [3]
The most frequent use of PEFR measurement is in home monitoring of asthma, where it can be beneficial in patients for both short- and long-term monitoring. When properly performed and interpreted, PEFR measurement can provide the patient and the clinician with objective data on which to base therapeutic decisions.
Indications
Indications for PEFR measurement are as follows:
-
Monitoring of asthma [4]
-
Monitoring effects of ozone and other air pollutants on respiratory function [5]
-
Monitoring of chronic obstructive pulmonary disease (COPD) [6]
A study by Murata et al indicated some usefulness of PEFR measurements in patients with COPD for daily monitoring. [7] Another study used peak flow as a predictor of demise from COPD. [8]
Providing feedback on predicted PEFR may improve both perception of respiratory compromise and adherence to controller medications in urban ethnic minority children. [9]
A prospective study in Turkey found a training program that included PEFR measurement to be effective in increasing self-efficacy and improving asthma symptoms among children and adolescents aged 10 to 18 years. [10]
Contraindications
No contraindications exist for PEFR measurement.
Technical Considerations
Best practices
In 2007, an expert panel of the National Asthma Education and Prevention Program (NAEPP) recommended periodic assessment of pulmonary function by spirometry or PEFR monitoring. [11] If PEFR monitoring is performed, a written asthma action plan should use the patient’s personal best peak flow, rather than published norms, as a reference value.
The panel recommended consideration of long-term daily PEFR monitoring or home peak flow rate assessment during exacerbations for patients with the following:
-
Moderate or severe persistent asthma
-
History of severe exacerbations
-
Poor perception of airflow obstruction and worsening asthma
-
Preference for peak flow rate monitoring rather than the use of a symptom-based asthma action plan
In managing chronic asthma, long-term daily PEFR monitoring may assist with the following measures:
-
Detecting early changes in asthma that may require therapy
-
Evaluating responsiveness to changes in therapy
-
Giving a quantitative measurement of improvement
-
Identifying temporal relations between environmental and occupational exposures and bronchospasm
The use of PEFR during acute asthma exacerbations is controversial. The 2007 NAEPP report suggested that measuring PEFR in acute asthma episodes helps determine the severity of exacerbations and assists in guiding therapeutic decisions in the home, school, practitioner’s office, and emergency department (ED). [11] However, Eid et al reported that PEFR measurement is unreliable for the classification of asthma severity. [3]
Procedural planning
Compliance with PEFR monitoring is limited by the difficulty that patients and their caregivers often have with keeping records. In one study of inner-city children, monitoring decreased 30% over the course of 3 weeks. [12] Kamps et al noted that children have poor compliance with recording PEFR measurements in symptom diaries. [13]
Self et al reported that PFMs are frequently incorrectly used by both children and adults. [14] PEFR measurement may be of lower utility in younger children [15] and elderly patients, but it has been shown to be of greater benefit in children who are poor or are members of minority groups. [16]
Ayala et al noted that provider communication about PEFR measurement was infrequent but that such communication predicted accurate PFM use in children with asthma. [17] In a study of adults, adherence was greatly improved by using an electronic device. [18]
Compliance with PEFR monitoring is also limited by the lack of ability, on the part of most clinicians, to interpret the data in a meaningful way. Numerous scales and charts are available, but many of them are difficult to interpret. [19, 20]
Outcomes
There are conflicting data regarding the efficacy of PEFR monitoring for improving asthma outcome. [21] Most studies have shown a benefit when PEFR monitoring is linked to a comprehensive program, combined with symptom diaries and patient education. [22, 23, 24]
However, one meta-analysis found PEFR monitoring to be equivalent to symptom-based asthma action plans. [25] Another study suggested that with symptom-based monitoring, some patients underestimate the severity of their condition and use medication inappropriately. [26] Gray et al reported that low baseline PEFR predicted unsuccessful treatment of adults with severe asthma. [27]
-
Peak expiratory flow rate (PEFR) measurement. Start with meter indicator at lowest level.
-
Peak expiratory flow rate (PEFR) measurement. Take in deep inspiration while standing.
-
Peak expiratory flow rate (PEFR) measurement. Exhale forcefully and rapidly with lips sealed around mouthpiece.
-
Peak expiratory flow rate (PEFR) measurement. Video courtesy of Therese Canares, MD, and Jonathan Valente, MD, Rhode Island Hospital, Brown University.
-
Peak flow meter (PFM). Courtesy of Therese Canares, MD, and Jonathan Valente, MD, Rhode Island Hospital, Brown University.
