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Using Quality-Control Analysis of Peak Expiratory Flow Recordings To Guide Therapy for Asthma

Peter G. Gibson, MBBS, FRACP; John Wlodarczyk, PhD; Michael J. Hensley, MBBS, PhD, FRACP, FAFPHM; Keith Murree-Allen, MBBS, FRACP, FCCP; Leslie G. BSc(Med) Olson, MBBS, PhD, FRACP; and Nicholas Saltos, MBBS, FRACP, FCCP, FRCP
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From John Hunter Hospital, the University of Newcastle, and Royal Newcastle Hospital, Newcastle, New South Wales, Australia. Acknowledgments: The authors thank the educators in the Asthma Management Service: Sr. P. Talbot, Sr. R. Toneguzzi, Sr. C. Kessell, and Mrs. P. Pratt. They also thank Gaye Sheather for secretarial assistance. Grant Support: In part by the Asthma Foundation of New South Wales. Requests for Reprints: Peter G. Gibson, Respiratory Medicine Unit, John Hunter Hospital, Locked Bag 1, Hunter Mail Exchange, Newcastle 2310, New South Wales, Australia. Current Author Addresses: Drs. Gibson, Murree-Allen, Olson, and Saltos: Respiratory Medicine Unit, John Hunter Hospital, Locked Bag 1, Hunter Mail Exchange, Newcastle 2310, New South Wales, Australia.

Copyright ©2004 by the American College of Physicians

Ann Intern Med. 1995;123(7):488-492. doi:10.7326/0003-4819-123-7-199510010-00002
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Objective: To compare the action points in published asthma management plans with those derived from quality-control analysis of peak expiratory flow recordings.

Design: Longitudinal observational study.

Setting: An ambulatory asthma education and management program in a tertiary care hospital.

Patients: 35 adults with asthma and exacerbation of asthma.

Measurements: Peak expiratory flow diaries and symptom recordings.

Results: Asthma action points from published asthma management guidelines had poor operating characteristics. The success rate was 35% when the action point was a peak expiratory flow rate less than 60% of the patient's best peak flow. The success rate improved to 88% when the action point was a peak expiratory flow rate less than 80% of the patient's best peak flow. Published action points had a high failure rate. Peak flow decreased to below the published action points during a stable period of asthma in 7% to 51% of patients studied. Action points defined using quality-control analysis did significantly better. A peak flow value less than 3 standard deviations below the patient's mean peak flow detected 84% of exacerbations and had a low failure rate (19%). Other quality-control tests had sensitivities of 91% and 71%. Quality-control action points could detect exacerbations up to 4.5 days earlier than conventional methods.

Conclusions: Individualized action points can be derived for patients with asthma by applying quality-control analysis to peak flow recordings. These action points are more sensitive in detecting exacerbations of asthma and have fewer false-positive results. Action plans developed in this manner should be more useful for the early detection of deteriorating asthma.


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Figure 1.
An example of a quality-control chart (x-bar chart) of peak expiratory flow recordings from a patient with asthma.

The mean daily peak expiratory flow is plotted on the y-axis. The lower control limit (LCL) is defined by quality-control analysis as 3 standard deviations below the mean peak flow value for the baseline period and is shown as a solid line. An asthma exacerbation was detected by conventional methods on day 18. The quality-control action points (tests 1, 2, and 3) were reached several days earlier. The day that the quality-control action point was first reached is shown by the number of that action point. For example, test 1 was first reached on day 16. Test 2 was first reached on day 13, which was 5 days before the detection of exacerbation by conventional methods.

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Grahic Jump Location
Figure 2.
Performance characteristics of published action points (●) and action points derived from quality-control analysis of peak expiratory flow (PEF) records (*).P

The action point derived using quality-control analysis (test 2) was significantly better than published peak flow points (PEF < 80% of that predicted and PEF < 60% of that predicted; < 0.002).

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