The use of objective measures of asthma severity in primary care: a report from ASPN - Ambulatory Sentinel Practice Network

Journal of Family Practice, August, 1995 by Robert A. Fried, Rebecca S. Miller, Larry A. Green, Philip Sherrod, Paul A. Nutting

Asthma is a common illness in the United States[1] and a frequent reason for ambulatory medical visits.[2] The overall economic impact of asthma in the United States is estimated to be at least $6 billion a year, most of which is attributable to hospitalization.[3] Appropriate outpatient management can reduce the need to hospitalize patients for acute exacerbations of the disease.[4]

Practice guidelines are one proposed way to assure that medical care is appropriate[5,6] and free of unintended variation.[7] Concerned about the rising death rate from asthma,[8] an expert panel convened by the federal government issued guidelines for asthma care in 1991.[9] Among the panel's recommendations was the use of objective measures of lung function to assess the severity of the disease in asthmatic patients.

There are several available choices of objective measure. The expert panel suggested that spirometry and peak expiratory flow rates (PEFR) are the most useful of the objective measures to assess asthma severity. In contrast, chest radiography has little value in determining the degree of airway compromise[10] and is useful chiefly for excluding other chest diseases. Determination of arterial oxygen content invasively or noninvasively also has limited utility as an objective measure of asthma severity. The inability of pulse oximetry to detect hypercarbia restricts its usefulness as a guide for asthma treatment,[11] and arterial blood gas measurement is rarely practical in the primary care office setting.

Like many other guideline statements, the 1991 recommendations on asthma diagnosis and management represent a consensus opinion of specialists in the field. An evidence-based approach, however, generally produces guidelines of higher quality.[12] The 1991 asthma guidelines have been severely criticized both for their lack of primary care perspective and the lack of supporting evidence.[13]

Research suggests that the act of creating and publishing a guideline does not affect physician bchavior.[14,15] Many explanations have been advanced, including physicians' lack of belief in the efficacy of the guideline within their own practice.[16] Because spirometry and PEFR are both old technologies, their baseline use in primary care practice, at the time when guidelines were first introduced, should reflect clinicians' level of confidence in their usefulness in the care of asthmatic patients. Alternatively, the lack of availability of tools and equipment could explain noncompliance with national guidelines. The Ambulatory Sentinel Practice Network (ASPN), therefore, studied the extent to which objective measures of lung function were available and used in the evaluation of asthmatic patients seen in primary care practices.

Methods

Study Setting

ASPN is a network of primary care practices that collaborate to conduct research about problems in primary care medicine. The network was created in 1978, and at the time of this study, included practices in 34 states and 4 Canadian provinces. In the aggregate, the practices include clinicians providing care for approximately 365,000 patients, who in turn made approximately 700,000 visits a year. ASPN's purpose, policies, and methods have been previously described.[17] The patients and problems seen in ASPN practices arc similar to those of the general US population seeking care from family physicians, as reflected in the 1990 National Ambulatory Medical Care Survey.[18]

Data Collection and Analysis

From April 20 through July 19, 1992, 38 ASPN practices collected information about patients seen for asthma using a weekly return card.[19] The weekly return card permits data capture by clinicians in "real time" without requiring retrospective chart review or reliance on codes assigned by others. Participating practices and their patient populations were representative of ASPN as a whole. Because asthma is a clinical diagnosis of exclusion that has no "gold standard,"[20] clinicians were asked to include all patients with a diagnosis of asthma and for whom asthma was at least one reason for the encounter. No attempt was made to standardize diagnostic criteria. Instead, practitioners were asked to include patients they would be willing to have coded for asthma (ICD-9 code 493.XX) and exclude patients with other respiratory disorders. Practices collected information about the sex and age of the patients; the duration of asthma in years; and whether there were available results of any of four separate objective measures of asthma (spirometry, PEFR, chest radiography, and oxygenation status as determined by the measurement of arterial blood gas or pulse oximetry). Clinicians indicated on the weekly return cards whether the patient had the test performed in the last 4 months (including on that day), more than 4 months ago, or never. The fourth response option, "unknown," was combined with the category "never" because each implied that objective data were not available to the clinician. Each practice also indicated the accessibility of each of the four measures and the frequency with which asthmatic patients visited. As in other ASPN studies based on weekly return cards, the data were collected in "real time," not as a retrospective chart review. This mechanism also permitted capture of two types of denominator information: proportion of the week in which the practice was available to its patients, and the total number of patients seen during the week.