Utility of Peak Expiratory Flow Monitoring* Prasoon Jain, MD; Mani S. Kavuru, MD, FCCP; Charles L. Ernerman, MD; and Muzaffar Ahmad, MD, FCCP (CHEST 1998; 114:861-876) Key words: asthma; patient education; peak expiratory flow; Abbreviations: BHR =bronchial hyperresponsiveness; BTPS=body temperature and pressure saturated with water vapor; ED=emergency department; NAEPP=National Asthma Education and Prevention Program; PEF=peak expiratory flow peak expiratory flow (PEF) monitoring has been advocated as an objective measure of airflow obstruction in patients with chronic asthma. 1 -3 All published asthma practice guidelines uniformly recommend the use of PEF monitoring as an adjunct to asthma education in selected groups of patients. 4 - 9 A number of proposed advantages of PEF monitoring remain unproved. The rationale for ambulatory PEF monitoring in chronic asthma is to provide early warning of incipient asthma exacerbation and to measure the severity of wors- ening airflow obstruction. The PEF monitoring might facilitate individualized self-management using preestablished criteria and allow more effec- tive communication between patients and their health-care providers for assessment of mainte- nance therapy. The widespread availability of in- expensive hand-held portable devices has made ambulatory PEF monitoring feasible. The poten- tial benefits of addition of PEF monitoring could include improving intermediate process parame- ters (eg, increase compliance with medications, avoidance of asthma triggers) or disease outcomes (eg, reduce prednisone bursts, emergency depart- ment [ED] visits). It is widely accepted that asthma patient educa- tion and self-management are essential for optimal patient outcome. Unfortunately, even after nearly four decades of use, many aspects of PEF moni- *From the Departments of Pulmonary and Critical Care Medi- cine (Drs. Jain and Kavuru ), and Emergency Medicine (Dr. Emerman ), and the Division of Medicine (Dr. Ahmad), The Cleveland Clinic Foundation, Cleveland, OH . Manuscript received September 26, 1996; revision accepted March 16, 1998. Correspondence to: Mani S. Kavuru, MD, FCCP, Director, Pul11Wnary Function Laboratory, The Cleveland Clinic Founda- tion, Department of Pulmonary & Critical Care Medicine, 9500 Euclid Ave/Desk A90, Cleveland, OH 44195 taring remain unclear. An important and largely unanswered question is whether PEF monitoring adds anything to a well-constructed, individualized asthma education program with management based on symptoms alone. Although some investi- gators have reported better patient outcome with peak flow-based asthma management compared with symptom-based management, there is no consensus (to our knowledge) and the published studies have a number of limitations. Many ques- tions remain unanswered regarding the subset of patients who are most likely to benefit from PEF monitoring. Also, it is still unclear how well PEF reflects airway inflammation and response to anti- inflammatory therapy. There is no uniform con- sensus as to which PEF index should be followed in the ambulatory setting. Finally, to our knowl- edge, no study has shown a favorable effect of PEF monitoring on asthma mortality. The aim of this review is to critically discuss the utility of PEF monitoring in asthma. First , we briefly review some technical aspects of PEF monitoring, including the equipment used to mea- sure PEF and the relationship between FEY 1 and PEF. Next, the issue of how well PEF parameters reflect measures of airway inflammation is consid- ered. We then discuss the limitations of clinical evaluation, the problem of poor perception , and the validity of PEF monitoring as an objective measure of airflow limitation in acute and chronic asthma. Finally, we critically analyze the currently available literature on the usefulness of PEF monitoring in the management of both chronic ambulatory asthma and acute asthma exacerbation in the ED and hospital setting. TECHNICAL CONSIDERATIONS What Is PEF? PEF is the largest expiratory flow achieved with a maximally forced effort from a position of maximum inspiration. 10 For spirometers, peak flow is expressed in body temperature and pressure saturated with water vapor (BTPS) conditions, but ambient condi- tions (without BTPS correction) are used for peak flowmeters. PEF is usually attained within the initial CHEST I 114 I 3 I SEPTEMBER, 1998 861