Joannie Shen; Michael Johnston; Ron D Hays


Expert Rev Pharmacoeconomics Outcomes Res. 2011;11(4):447-453. 

In This Article

Asthma Exacerbation

Leading international asthma guidelines have consistently described the goals of asthma treatment as not only controlling current symptoms, but also preventing recurrent AEs. These guidelines include the Global Initiative for Asthma and the National Heart, Lung and Blood Institute/National Asthma Education and Prevention Program: Expert Panel Report 3.[1,102] Experts have argued that AEs may be the most important clinical outcome because they constitute a great risk, cause distress to patients and their families and generate substantial healthcare system costs. AE episodes vary considerably in speed of onset and time to resolution, ranging from a few minutes to several weeks. While severe AEs are more common in patients with poorly controlled asthma, they may also occur in patients with well-controlled asthma. For example, an airway infection can overwhelm the asthma control achieved previously by use of combination therapeutics. AEs are defined by use of healthcare, systemic corticosteroids and rescue medicine.

The recently published American Thoracic Society (ATS)/European Respiratory Society (ERS) Statement: Asthma Control and Exacerbations (joint ATS/ERS statement), provides a comprehensive review of the definitions of AE, asthma control and severity.[2] The joint ATS/ERS statement defined AEs as events characterized by a change from the patient's previous status and it stratified AEs by severity. In the clinical setting, the severity of AEs varies considerably. AEs can be identified by changes in symptoms, rescue medication use or lung function that differ from the patient's usual day-to-day variation. Severe AEs are events that include at least one of the following: requirement for systemic corticosteroids; an increase from a maintenance dose of daily medicine for at least 3 days; or a hospitalization or emergency department (ED) visit requiring systemic corticosteroids. Moderate asthma exacerbations are defined by temporary changes in treatment and include one or more of the following: deterioration in symptoms; deterioration in lung function; or increased rescue bronchodilator use lasting for 2 days or more, but requiring neither a hospitalization or ED visit, nor systemic corticosteroids.

Other recommendations proposed by expert workgroups and researchers differed in part from the joint ATS/ERS statement. However, there may be difficulty in distinguishing moderate AEs from worsening of symptom control. Defining AEs by systemic corticosteroid use, ED use or hospitalizations is consistent with the joint ARS/ERS statement's definition of severe AE, without including the less severe moderate AE category.

Measures of asthma-specific healthcare use are often applied as indirect indicators of intervention efficacy and asthma control. These measures, whether made prospectively or retrospectively, may include outpatient care, pharmacy-dispensing data, ED visits and hospitalization. Measures of asthma-specific events can be obtained from survey data, administrative claims or health services encounter data.

Each type of data source has limitations. Administrative data are rich in details on duration, diagnosis and treatment, but errors and bias may occur owing to coding and billing issues. Survey data collection relies on self-reports and is affected by recall bias.[3] Unscheduled outpatient visits could indicate AEs or worsening of asthma control. Asthma-specific systemic corticosteroid use for at least 3 days (higher than maintenance dose) or ED visits or hospitalization or both, indicate loss of asthma-symptom control and severe AE. Consistent methods and reporting of these outcomes allow comparability across studies. When measuring counts of asthma healthcare events, study duration is an important consideration; adverse outcomes such as hospitalizations are relatively rare – events may fluctuate owing to seasonal factors and may be under- or over-represented in studies of less than 12 months duration.


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