Lesson 11, Volume 12—Peak Flow: Myths & TruthsBy Susan Janson, DNSc, RN Objectives
Key wordsasthma; asthma action plan; clinical management; monitoring; peak expiratory flow Peak expiratory flow (PEF) provides a simple, quantitative, and reproducible measure of the existence and severity of airflow obstruction. It is defined as the highest flow achieved at the mouth during a forced exhalation (see Fig 1). Accurate measurement requires maximal inspiration followed by maximal forced exhalation. PEF can be measured either via spirometer in liters per second or on a hand-held, portable peak flowmeter in liters per min. All peak flowmeters should meet the American Thoracic Society (ATS) recommendations for monitoring devices.1 Since PEF can be measured with a brief, forceful expiratory maneuver, it provides a rapid assessment of airflow limitation and can be helpful in monitoring the progress of obstructive lung disease and response to treatment. PEF reflects primarily large airway caliber and when measured by a peak flowmeter is dependent on patient effort and respiratory muscle strength. Maximal effort is required since the measurement is effort-dependent, but prolonged effort is not necessary since PEF occurs within the first 150 ms of expiration. Figure 1. Flow volume curve showing normal flow and volume relationships and airflow obstruction (dotted line).
Because the measurement of PEF is dependent on effort and technique, attention should be paid to training patients in the technique of measurement to obtain a valid measure. Patients will need demonstration, practice, and frequent reviews of the proper technique (see Fig 2). The measure can be performed either sitting or standing, but the neck must not be flexed. The mouthpiece should be gripped between the teeth and over the tongue. Spuriously high values are obtained if high explosive pressure is generated in the mouth ("jetting" or "spitting") caused by the tongue near the mouthpiece or sudden glottis opening when it was previously closed. Submaximal expiration will produce erroneously low values. Errors can only be corrected by frequent observation of patient technique. The highest value of three successive technically correct blows should be recorded as the measured value.2
Currently, ambulatory PEF monitoring measured on
a portable peak flowmeter, is recommended in national and international
guidelines as a useful self-management activity for patients in
the long-term management of asthma. Emphasis is placed on using
the peak flowmeter as a monitoring tool only and not as a diagnostic
device. Although PEF and forced expiratory volume in 1 sec (FEV1)
are closely correlated (r=.85) this correlation is not sufficient
to allow PEF to substitute for spirometry.3 Although
ambulatory PEF monitoring has been used in other chronic obstructive
lung diseases, its chief usefulness is for patients with asthma
whose airflow obstruction is variable. The importance of a single
measurement is not clear, rather, trends in PEF measured over time
provide more information about airflow obstruction. When patients
present with symptoms of asthma but have normal spirometry, a period
of PEF monitoring may be useful to detect diurnal variation. PEF
will usually be lowest in the morning when awakening and highest
in mid-afternoon.4 PEF measurements taken later in the
day, although more convenient, will underestimate the diurnal variation.
A 20% or greater difference between the morning and afternoon measurements
suggests asthma. Patients with variable airflow obstruction and
poorly controlled asthma may have wide swings daily in PEF (see
Fig 3). Figure 3. Wide diurnal variation in peak expiratory flow in a patient with unstable, poorly controlled asthma and variable airflow obstruction.
Advantages and Limitations of Peak Expiratory Flow MonitoringThe rationale for recommending PEF home monitoring for asthma self-management is that it allows both the patient and the physician to assess and monitor the course of the illness in a partnership approach that permits early detection of exacerbations and subsequent treatment. Support for this approach is based on evidence that neither the physician nor the patient can accurately assess the severity of asthma and exacerbations without objective measures of lung function. In one clinical study, 60% of 255 adults with asthma who estimated the severity of their asthma on a visual analogue scale and concurrently measured PEF, had no correlation between perceived severity and actual PEF.5 Patients who have difficulty perceiving airflow obstruction include 24 to 27% of elderly patients 6 and patients who have had near-fatal asthma exacerbations.7 Asthmatic patients with these characteristics may well benefit from monitoring objective measures of lung function on a regular basis to detect developing exacerbations. Although most patients can detect symptoms of dyspnea, wheezing, and chest tightness, symptoms are highly individual and perception and sensitivity to changes are variable. Therefore, the recommendations for PEF monitoring in chronic asthma are based on the following potential advantages: (1) detection of increasing airflow obstruction allowing earlier treatment; (2) monitoring control of asthma by adjusting treatment up or down; (3) providing a form of feedback to the patient about the state of the airway; (4) identification of environmental exacerbating factors; and (5) evaluation of response to treatment. There are several potential problems with PEF monitoring. The validity and reliability of the PEF measurements depend on correct technique and maximal effort. Technique may wane and become inadequate over time necessitating repeated review, practice, and reinforcement. Monitoring devices may fail and therefore, periodic comparison of the PEF measured on the portable flowmeter should be compared to PEF measured by spirometry. Although not expected to be the same values, the comparison should remain consistent. Even with correct technique, patients make transcription errors or fabricate values when recording them manually. These problems have prompted the development of electronic peak flowmeters, capable of data storage and eliminating the need for keeping manual records. No published studies are yet available on the efficacy of these electronic devices but they seem to be highly acceptable to patients. Another problem is that patients have difficulty maintaining adherence to long-term, regular monitoring due to inconvenience, lack of motivation, or lack of a useful self-management plan based on peak flow.8 In one study of compliance with short-term PEF monitoring among inner city asthmatic children, monitoring with a electronic flowmeter was compared to monitoring with a simple flowmeter.9 Both groups recorded the measured values in diaries and the electronic flowmeter group was unaware the flowmeter was recording actual values, dates, and times. The percent of days with missing data increased to 10.6% over 3 weeks in both groups and the electronic flowmeters indicated a significantly higher number of missed recordings than the diaries indicated. Patients and their parents considerably overestimated their use of the flowmeter in the manual records. It should be remembered that patients are unlikely to continue recording measurements if they aren't told what the numbers mean and how to use these values in self-management of asthma. PEF Monitoring as a Clinical InterventionPEF monitoring has been advocated as a useful way to provide patients with an early warning symptoms for detecting exacerbations and instituting an action plan. Four clinical studies, three randomized clinical trials,10-12 and one uncontrolled study13 found that comprehensive asthma management with PEF monitoring as a component, produced significant improvements in disease status and health outcomes. The three randomized trials10-12 and the uncontrolled pretest/post-test study13 tested a treatment program that included self-managed medication plans, appropriate medications, education, and PEF monitoring. In one of the earliest randomized controlled studies of PEF-directed self-management in 24 asthmatic patients, there was a 34-fold reduction in sensitivity to histamine and a 16% increase in FEV1 in the self-management group after 18 months.10 In the two recent randomized controlled trials11,12 and in the uncontrolled trial13 there were significant improvements in lung function, symptoms, number of urgent care visits, number of missed work days, quality of life, and medication use after 6 months in two studies11,13 and after 12 months in one12 when PEF monitoring was combined with an action plan for self-management of exacerbations and patient education. Although improvement in all measured outcomes in these positive studies was statistically significant, the relative contribution of PEF monitoring to observed improvements could not be isolated from the other components of the intervention. Monitoring may result in changes in self-management behavior. One randomized trial (n=28) of PEF monitoring alone demonstrated that patients who measured PEF when they detected asthma symptoms used significantly less beta-agonist rescue inhaled medication than did those in the control group who did not measure PEF during symptom episodes.14 In contrast, three randomized controlled trials comparing daily PEF monitoring with symptoms monitoring or to usual episodic care15-17 found no significant differences in any of the measured outcomes. In a study of 115 adults and children cared for in one practice setting, patients were randomly assigned to either a PEF-directed self-management plan or a symptoms-only plan.15 Notably, both groups improved significantly in the outcomes measured including hospitalizations, urgent care visits, doctor consultations, or need for rescue nebulizer treatments, but there were no differences between the groups. All patients had access to a nursing advisor, specially trained in asthma management and this may have served as an important intervening variable. In a large trial, 569 asthmatic adults who had never been prescribed a peak flowmeter were randomized to asthma care with routine PEF monitoring or usual care without monitoring.16 After 12 months there were no significant differences in pulmonary function, medication needed, doctor visits, or hospitalizations. Analysis of a separate group which had previously been given peak flowmeters by their physicians indicated these patients were more likely to have severe asthma. Similarly, in another randomized trial (n=72) of PEF monitoring in mild asthma (FEV1>80%predicted) no differences in lung function, morbidity, quality of life, or decision-making outcomes were detected between the PEF group and the group receiving usual care.17 However, when the PEF group was queried at the end of the study, 82% reported the peak flowmeter was helpful to them, and 88% still knew where the flowmeter was. Despite this enthusiasm the data did not show any advantage of PEF monitoring over more usual approaches. In summary, none of these negative studies found significant differences between experimental and control groups in the health outcomes measured including lung function, symptom frequency, quality of life, hospitalizations, medication use, and urgent doctor visits. However, most studied only patients with mild asthma, a group that is not expected to benefit much from PEF monitoring. Almost all the published PEF monitoring studies suffer from study design and procedural problems, such as selection bias, unequal groups, small sample size, and attrition problems, making it difficult to come to firm conclusions. Taken together, the findings of all the PEF monitoring studies suggest that there appears to be no significant advantage of PEF monitoring in patients with mild asthma. Based on all these findings, recent updates of the guidelines for asthma management18 recommend PEF monitoring for patients with moderate-to-severe persistent asthma or unstable asthma. These patients seem more likely to benefit from long-term daily monitoring. Short-term PEF monitoring may be helpful for assessing the severity of the patient's asthma and evaluating response to new therapy and to changes in the treatment plan. Clinical RecommendationsPatients who are given a peak flowmeter should be shown how to use it and how to establish their personal best PEF. The personal best should be used as the target value in their action plan. The personal best can be estimated after 2-week monitoring period when the patient records PEF 2-4 times per day. Generally, the best PEF is achieved in the afternoon after maximal therapy has stabilized the patient's asthma.4 Optimal information can be obtained by measuring PEF on awakening in the morning before inhaling beta-agonist medication and in the mid-afternoon after taking inhaled beta agonist. A course of oral corticosteroid therapy may be necessary to bring the asthma under control and to allow determination of the personal best PEF. High outlying values should not be used as the personal best if they occur only once as they are considered as spurious measurements. Periodic reassessment of the personal best PEF is necessary to account for disease progression or growth in children. When daily PEF monitoring is used, patients should measure PEF on waking in the morning before inhaling bronchodilator medications. The morning PEF expressed as percent of personal best, appears to correlate best with the degree of bronchial reactivity.19 Guidelines recommend that the patient use inhaled beta-agonist medication if the morning value is <80% of personal best and values <50% indicate a severe exacerbation requiring medical attention and additional medication. These action points are arbitrary and should be individualized to the patient's level of severity and risk. Often the action points are used to create color zones modeled after a traffic light where patients are directed to take specific actions detailed in the action plan. For example common plans indicate PEF measurements >80% of personal best are in the green zone, indicating all clear and with the directions to follow the usual daily treatment plan. The yellow zone is >50% but <80% of personal best and indicates "caution" requiring specific actions, such a taking puffs of a rescue medication or increasing the puffs of an inhaled corticosteroid. The red zone is <50% of best and indicates a severe exacerbation requiring immediate medical care and rescue medications. Patients with values in the red zone are directed to call their physician and go to the nearest hospital emergency department. An example of an action plan based on PEF measurements is provided in Figure 4.
Patients who are monitoring PEF over time should bring the PEF flowmeter to each clinical appointment so that technique and measurement reliability can be assessed. The same brand of peak flowmeter should be used over time because different brands can give significantly different values of PEF.20 There is no universal normative standard for PEF, although currently available published normative standards use height, age, and gender to established a range of predicted values.21 PEF rates differ across racial and ethnic populations with the largest differences being between African-Americans and Caucasians for a given height.22 Therefore, the PEF measurements can only be considered valid within individuals over repeated measurements. The durability and reliability of peak flowmeters has not been studied adequately enough to provide recommendations about when peak flowmeters should be replaced. When the flowmeter is replaced, patients should reestablish their personal best PEF on the new flowmeter and update the PEF action plan. In summary, PEF monitoring can be a useful clinical assessment tool, especially for asthmatic patients with moderate-to-severe persistent asthma. Linking the PEF measurements to specific asthma self-management plans with appropriate actions and feedback will enhance its effectiveness and usefulness as a monitoring tool. References1. American Thoracic Society. Standardization of spirometry: 1994 update. Am J Respir Crit Care Med 1995;152:1107-36 2 Enright PL, Sherrill DL, Lebowitz MD. Ambulatory monitoring of peak expiratory flow. Reproducibility and quality control. Chest 1995;107:657-61 3. Connelly CK, Chan NS. Relationship between different measurements of respiratory function in asthma. Respiration 1987; 52:22-33 4. Quackenboss JJ, Lebowitz MD, Krzyzanowski M. The normal range of diurnal changes in peak expiratory flow rates. Relationship to symptoms and respiratory disease. Am Rev Respir Dis 1991;143:323-30 5. Kendrick AH, Higgs CM, Whitfield MJ, et al. Accuracy of perception of severity of asthma: patients treated in general practice BMJ 1993;307:422-24 6. Connolly MJ, Crowley JJ, Charan NB, et al. Reduced subjective awareness of bronchoconstrition provoked by methacholine in elderly asthmatic and normal subjects as measured on a simple awareness scale. Thorax 1992;47:410-13 7. Kikuchi Y, Okabe S, Tamura G, et al. Chemosensitivity and perception of dyspnea in patientswith a history of near-fatal asthma. N Engl J Med 1994;330:1329-34 8. Chmelik F, Doughty A. Objective measurements of compliance in asthma treatment. Ann Allergy 1994;73:527-32 9. Redline S, Wright EC, Kattan M, et al. Short-term compliance with peak flow monitoring: Results of a study of inner city children with asthma. Ped Pulmol 1996;21:203-10 10. Woolcock AJ, Yan K, Salome CM. Effect of therapy on bronchial hyperresponsiveness in the long-term management of asthma. Clin Allergy 1988; 18:165-76 11. Ignacio-Garcia JM, Gonzalez-Santos P. Asthma self-management education program by home monitoring of peak expiratory flow. Am J Respir Crit Care Med 1995; 151:353-59 12. Lahdensuo A, Haahtela T, Herrala J, et al. Randomized comparison of guided self management and traditional treatment of asthma over one year. BMJ 1996;312:748-52 13. Beasley R, Cushley M, Holgate ST. A self management plan in the treatment of adult asthma. Thorax 1989; 44:200-04 14. Janson-Bjerklie S, Shnell S. Effect of peak flow information on patterns of self-care in adult asthma. Heart and Lung 1988; 17(5):543-49 15. Charlton I, Charlton G, Broomfield J, et al. Evaluation of peak flow and symptoms only self management plans for control of asthma in general practice. BMJ 1990;301:1355-59 16. Grampian Asthma Study of Integrated Care. Effectiveness of routine self-monitoring of peak flow in patients with asthma. BMJ 1994; 308:564-67 17. Jones KP, Mullee, MA, Middleton M, et al. Peak flow based asthma self-management: a randomized controlled study in general practice. Thorax 1995;50:851-57 18. National Heart, Lung, and Blood Institute. National Asthma Education and Prevention Program. Expert Panel Report 2: Guidelines for the Diagnosis and Mangement of Asthma. National Institutes of Health. Publication No. 97-4051, Bethesda, Md: NIH, 1997. 19. Reddel HK, Salome C.M, Peat J.K, et al. Which index of peak expiratory flow is most useful in the management of stable asthma? Am J Respir Crit Care Med 1995; 151:1320-25 20. Jackson AC. Accuracy, reproducibility, and variability of portable peak flow meters. Chest 1995;50:851-57 21. Nunn AJ, Gregg I. New regression equations for predicting peak expiratory flow in adults. Br Med J 1989; 298:1068-72 22. Coultas DB, Gong H Jr, Grad R, et al. Respiratory diseases in minorities of the United States. Am J Respir Crit Care Med 1994;149:S93-S131 |
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