Porth's Essentials of Pathophysiology, 4e

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Respiratory Function

U N I T 6

TABLE 23-1 Classification of Asthma Severity

Symptoms, Interference with Normal Activities, and Frequency of Short-Acting β 2 -Agonist Use Symptoms ≤ 2 days a week No interference with normal activity Short-acting β 2 -agonist use <2 days a week Symptoms 2 days a week but not daily Minor limitation in normal activity Short-acting β 2 -agonist use ≥ 2 days a week but not daily Symptoms daily Some limitation in normal activity Short-acting β 2 -agonist daily Symptoms throughout the day Extreme limitation in normal activity Short-acting β 2 -agonist several times a day

Asthma Severity

Nighttime Awakenings

Lung Function

Mild

<2 times a month Normal FEV 1.0

between exacerbations

intermittent

FEV 1.0 FEV 1.0

>80% predicted

/FVC normal

Mild persistent

3–4 times a month FEV 1.0

>80% predicted

FEV 1.0

/FVC normal

Moderate

>1 time a week

FEV 1.0

>60% normal but <80%

persistent

but not nightly

predicted

FEV 1.0 FEV 1.0 FEV 1.0

/FVC reduced 5%

Severe

Often 7 times a week

<60% normal

persistent

/FVC reduced >5%

FEV 1.0 , forced expiratory volume in 1 second; FVC, forced vital capacity.

Adapted from National Lung, Heart, and Blood Institute National Asthma Education and Prevention Program. Expert Panel Report 3: Guidelines for Diagnosis and Management of Asthma. Bethesda, MD: National Institutes of Health; 2007.

diagnosis of asthma, they can be used in clinics and phy- sicians’ offices and by persons in their home to provide frequent measures of flow rates. Day–night (circadian) variations in asthma symptoms and PEF variability can be used to indicate the severity of bronchial hyperre- sponsiveness. The person’s best performance is estab- lished from readings taken over several weeks. This often is referred to as the individual’s personal best and is used as a reference to indicate changes in respiratory function. A PEF below 40% of the predicted or personal best during an acute asthmatic attack indicates a severe exacerbation and the need for immediate intervention, and a PEF below 25% of the predicted or personal best indicates a life-threatening attack. 19 Successful management of bronchial asthma requires control of factors contributing to asthma severity and pharmacologic treatment. Control measures are aimed at prevention of exposure to allergens and irritants. They include education of the person and family regard- ing known triggers; therefore, a careful history is needed to identify all contributory factors. Annual influenza vaccination is recommended for persons with persistent asthma. A program of desensitization may be undertaken in persons with persistent asthma who react to allergens, such as house dust mites, that cannot be avoided. This involves the injection of selected antigens (based on skin tests) to stimulate the production of IgG antibodies that block the IgE response. A course of allergen immuno- therapy is typically of 3 to 5 years’ duration. 19 Traditionally, drugs used to treat asthma were cat- egorized according to their predominant mechanism of action—relaxation of bronchial smooth muscle (bron- chodilator) and suppression of airway inflammation (anti-inflammatory drugs). A more recent classification divides asthma medications into two general categories

according to their roles in the overall management of asthma symptoms (quick-relief or long-term mainte- nance medications). 19 Quick-relief Medications. The quick-relief medications include the short-acting β 2 -agonists, anticholinergic agents, and systemic corticosteroids. 19,21,31 The short- acting β 2 -agonists relax bronchial smooth muscle and provide prompt relief of symptoms, usually within 30 minutes. They are administered by inhalation (i.e., metered-dose inhaler [MDI] or nebulizer). The anticholinergic agents block cholinergic recep- tors and reduce intrinsic vagal tone that causes broncho- constriction. These medications, which are administered by inhalation, produce bronchodilation by direct action on the large airways but do not change the composition or viscosity of the bronchial mucus. It is thought that they may provide some additive benefit for treatment of asthma exacerbations when administered with inhaled β 2 -agonists. A short course of systemic corticosteroids, admin- istered orally or parenterally, may be used for treating the inflammatory reaction associated with the late-phase response. Although their onset of action is slow (>4 hours), systemic corticosteroids may be used in the treatment of moderate to severe exacerbations because of their action in preventing the progression of the exacerbation, speed- ing recovery, and preventing early relapses. Long-term Medications. The long-term medications are taken on a daily basis to achieve and maintain con- trol of persistent asthma symptoms. They include inhaled corticosteroids, long-acting bronchodilators, cromolyn and nedocromil, leukotriene receptor antagonists, and theophylline. 19,21,31 The corticosteroids are considered the most effective anti-inflammatory agents for use in