PRAS00N JAIN, MD Dr. Jain is a fellow in the Department of Pulmonary and Critical Care Medicine at the Cleveland Clinic. MANI S. KAVURU, MD Dr. Kavuru is director of the Pulmonary Function Laboratory at the Cleveland Clinic. A practical guide for peak expiratory flow monitoring in asthma patients • KEY POINTS: • ABSTRACT: The peak expiratory flow rate is an objective measure of As many as 15% of patients cannot airflow obstruction that patients can learn with little difficulty, and which perceive severe airflow obstruction, provides physicians objective information for assessing a patient's condi- and studies show that physicians often tion. We outline how to use peak flow monitoring as part of an asthma misjudge the severity of asthma attacks. treatment plan. n assessing and treating asthma, the signs and symptoms are not Peak flow monitoring at home is enough: many patients and physicians alike underestimate the indicated for patients older than 5 severity of airway obstruction. To obtain objective information, we years with moderate to severe asthma, advocate measuring the peak expiratory flow (PEF, or peak flow) and gives physicians an objective rate. Our patients with moderate to severe asthma measure their assessment of airflow obstruction. Ipeak flow at home using inexpensive, compact meters and record the readings in an asthma diary, which we review at follow-up visits. A reading of 50% or less of the patient's personal best peak flow • WHY MEASURE PEAK FLOW? reading indicates quick action is Recent advances in understanding the pathogenesis of asthma have needed, while a reading of 50% to shifted the emphasis of treatment. Instead of controlling the symptoms 80% indicates a potential problem. of bronchospasm only with inhaled beta2 agonists and methylxan- thines, we also try to control the underlying chronic airway inflamma- Patient education is crucial and must tion with inhaled anti-inflammatory agents.1 include specific instructions on what to However, these advances have not translated into improved con- do in case of low peak flow readings. trol in the general asthmatic population. Approximately 5% of adults and 10% of children in the United States have asthma, and its preva- lence seems to be increasing, especially in children. From 1982 through 1991, the rate of death due to asthma increased by 62% in the United States.2 Hospital admissions for asthma have increased in recent years. Possible reasons for these trends are inadequate access to health care, suboptimal maintenance pharmacotherapy, and delay in starting appropriate therapy because patients, relatives, and physicians fail to recognize the severity of an asthma attack. CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 64 • NUMBER 4 APRIL 1997 2 1 3 Downloaded from www.ccjm.org on September 28, 2021. For personal use only. All other uses require permission. PEAK EXPIRATORY FLOW MONITORING • JAIN AND KAVURU LJ TABLE 1 volume in 1 second (FEVJ that is less than 50% of predicted.^ No demographic or clin- RATIONALE FOR PEAK EXPIRATORY FLOW MONITORING ical feature can help the physician predict which patients will be "good perceivers" or At home "poor perceivers." To detect worsening airflow obstruction early in patients, who may perceive symptoms poorly Clinical signs are also unreliable Hyperinflation and wheezing that is high- To guide patients in taking medications pitched, loud, and biphasic are thought to be To improve asthma control signs of severe airflow obstruction. However, To reduce asthma-related morbidity several studies have shown that even experi- enced physicians often misjudge the severity To improve perception of acute airflow obstruction of an asthma attack,^5 and data suggests that patients can gauge the severity of an attack In the emergency department better than their physicians can.6 To objectively assess the severity of asthma attacks To assess response to therapy Underestimating asthma severity leads to undertreatment To predict early the need for hospital admission Physicians and patients need an objective To Identify need for arterial blood gas analysis measure of airflow obstruction to guide them To predict relapse after discharge from the emergency department in managing asthma attacks promptly, because underestimating the severity of airflow obstruction can delay appropriate therapy. In hospitalized patients Such delay may allow lung function to worsen To assess therapeutic response progressively, predisposing patients to near- To document clinical improvement at discharge fatal asthma attacks and placing them at high- er risk of asthma-related death. In occupational asthma Peak flow monitoring is practical To demonstrate airflow obstruction at the workplace The peak flow rate is the most practical mea- To identify asthma triggers sure in outpatients,7-9 as the monitoring devices are inexpensive (costing from $15 to ••••••••••^^••••••••••••••••••••••••MHBHMHHlI $40), portable, and easy to use. Patients as young as 5 years can master the technique with Patients' perceptions of symptoms are unreliable minimum training and keep an accurate record. The patient's own perceptions of chest tight- Admittedly, the FEVi is more accurate, as ness, cough, wheezing, and shortness of breath it reflects changes in large and medium-sized strongly influence the treatment he or she airways, whereas the peak flow reading reflects receives. When patients seek advice over the changes in the large airways only. Peak flow telephone, these perceptions are often the readings correlate well with FEV| readings, only kind of information available to the but not uniformly. Therefore, a peak flow physician. reading is not an adequate substitute for office Unfortunately, these symptoms are spirometry. However, serial peak flow mea- unreliable. Numerous clinical and experi- surements are acceptable for monitoring lung mental studies show that many asthma function. patients cannot accurately evaluate the severity of airflow obstruction. As many as Studies have been equivocal 15% of patients cannot perceive even severe Studies that compared the outcomes of airflow obstruction—a forced expiratory patients treated according to peak flow val- 196 CLEVELAND CLINIC JOURNAL OF MEDICINE VOLUME 64 • NUMBER 4 APRIL 1997 Downloaded from www.ccjm.org on September 28, 2021. For personal use only. All other uses require permission. ues vs symptoms have yielded conflicting expensive equip- TABLE 2 results. The failure to show clear benefit of ment, has a greater INDICATIONS FOR PEAK management based on peak flow readings clinical value than EXPIRATORY FLOW MONITORING compared with conventional management is the peak flow read- AT HOME very controversial, and may be the result of ing. Studies showed differences in "action points" used in the that patients who Moderate to severe asthma studies. needed hospital ad- Labile and poorly controlled symptoms Most studies of outcomes used peak flow mission after receiv- values of less than 70% of the patient's per- ing initial care in Increasing need for rescue beta2 agonists sonal best as an initial indication to alter the the emergency de- Repeated need for oral prednisone therapy treatment, or "action point." In a recent partment had lower Frequent emergency visits for asthma 10 study, Gibson and colleagues found a better peak flow rates both exacerbations peak flow-based action point: readings on 2 at initial presenta- Recent hospital admission for asthma of 3 consecutive days that were between 2 tion and at the time and 3 standard deviations below the patient's of disposition from Near-fatal asthma attack mean value. This criterion was significantly the emergency Poor perception of asthma symptoms more sensitive and specific than criteria room.20'21 Peak flow based on a percentage of the patient's per- monitoring may sonal best reading and detected exacerba- reduce the need for tions several days sooner, at least in retro- arterial blood gas analysis in as many as 40% spect. of patients receiving emergency therapy for Nevertheless, we believe that peak flow asthma exacerbations.22-23 Practice guidelines monitoring has a sound and logical rationale based on peak flow monitoring have been (TABLE 1) and we will discuss our specific rec- shown to reduce unnecessary hospital admis- ommendations for action points in the section sions.24 on practical recommendations, below. The National Asthma Education and On the basis of frequency of asthma symp- Prevention Program recommends peak flow toms, peak expiratory flow (expressed as a per- monitoring for all patients with acute asthma centage of the patient's personal best score), exacerbation and suggests that the peak flew and peak flow variability, asthma is classified value should be at least 70% of the predicted as mild, moderate, and severe. value at the time of discharge from the emer- Measure the Patients with mild asthma do not need gency department.25 Unfortunately, many peak flow rate peak flow monitoring,11-13 but patients with physicians do not measure the peak flow rate before and 10 to moderate to severe asthma appear to bene- in this situation. Also, patients do not typical- 15 minutes after fit,13-15 because it facilitates close monitoring ly receive clear instructions about peak flow giving a beta2 of lung function and may promote use of monitoring before discharge.26 agonist inhaled steroids and early institution of oral In these patients, the peak flow should be steroid therapy whenever appropriate. measured before starting therapy and fre- In many randomized studies that com- quently thereafter. Measuring the peak flow pared peak flow-based management with con- before and 10 to 15 minutes after giving a ventional symptom-based treatment, the out- beta2 agonist provides a fair assessment of how comes improved even in the control groups, well bronchospasm responds to inhaled bron- probably because all patients in these studies chodilators in the short term. In addition, the received asthma education. These findings peak flow should be measured at the time of concur with those in previous studies of asth- discharge from the emergency department, to ma education.16-18 document that airflow has improved.