Diagnostic criteria

The diagnosis of asthma is based on assessment of three components: symptoms, lung function (airflow obstruction), and airway hyperresponsiveness. A clinical diagnosis is suspected if such symptoms as wheezing, episodic breathlessness, chest tightness, or nocturnal cough are present. Asthma should also be considered if these symptoms occur in association with exercise or environmental exposure or if there is a personal or family history of atopy.3,5-7    

Assessing variability in lung function with spirometry provides an indirect measure of airflow limitation and determines the severity of airflow obstruction. Measurements of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) are most useful. Peak expiratory flow (PEF), easily measured with a handheld meter, can also determine expiratory flow limitation and variability, but it is not interchangeable with FEV1. A decrease in FEV1 to <80% predicted is consistent with airflow obstruction, and an improvement of at least 12% after inhalation of a bronchodilator (albuterol or ipratropium bromide) reflects hyperresponsiveness.   


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For patients whose symptoms are consistent with asthma but who have normal lung function, bronchoprovocation tests with methacholine, histamine, or exercise challenge should be performed to determine airway hyperresponsiveness. The methacholine PC20 is the dose of methacholine that causes a 20% decrease in a patient’s baseline FEV1, measured after inhaling normal saline. A negative test, i.e., FEV1 remains >80% of baseline, excludes asthma in adults with 95% certainty. A positive test confirms the presence of bronchial hyperresponsiveness, although it is not specific for asthma.3,5-7  

Aging affects pulmonary physiology and pulmonary function testing. The normal decline in FEV1 is approximately 25-35 mL/year beginning at age 35. Older adults may not demonstrate a 12% improvement in FEV1 with a bronchodilator because of chest-wall restriction (changes in posture, e.g., osteoporosis; obesity) and the natural decline in FEV1. Therefore, if asthma is suspected, a reduced methacholine PC20, e.g., <4 mg/mL, is considered diagnostic of airway hyperresponsiveness in contrast to a PC20 <8 in younger adults and adolescents.2

Severity classification

Asthma severity should be determined and categorized by clinical features (symptoms and lung function) before treatment is initiated.5-7 For patients already receiving treatment, severity classification is based on the clinical features present and the stage of the daily medication regimen the patient is currently following. A patient at the mild persistent level who is receiving appropriate medication but continues to have symptoms should be reclassified as having moderate persistent asthma.5-7 Treatment is then adjusted, and once the patient is stable for three months, he or she can be reclassified according to the new maintenance treatment.

Treatment

The management of asthma should include patient education, self-monitoring of symptoms and lung function with a minimum of daily peak expiratory flow measurements, avoidance of exposure to risk factors, a daily medication plan, and an individualized plan for managing exacerbations. Underlying conditions, such as GERD, should also be treated.    

Medication includes “controllers” to prevent symptoms and airflow limitation as well as “relievers,” which are used to reverse symptoms and airflow obstruction. The NIH-National Asthma Education and Prevention Program/Global Initiative on Asthma (NIH-NAEPP/GINA) guidelines recommend that treatment begin by identifying a specific asthma phenotype, i.e., mild, moderate, or severe persistent, and rely on response to stepwise therapy and patient education to achieve control.5-7    

For patients with intermittent asthma, controller medications are unnecessary, and only intermittent reliever (short-acting) medications, i.e., inhaled β2-agonist, ipratropium bromide, oral albuterol, or oral theophylline, are needed. Overuse of a short-acting β2-agonist can result in paradoxical bronchoconstriction in some individuals. Therapy should then be changed to a short-acting anticholinergic (ipratropium).