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SOURCE

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Source: Sorkness CA, Blake KV. Asthma. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146058008. Accessed April 13, 2017.

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DEFINITION

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  • Chronic inflammatory disorder of airways that causes recurrent episodes of wheezing, breathlessness, chest tightness, and coughing.

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ETIOLOGY

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  • Genetic factors.

  • Environmental exposures (see Risk Factors)

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PATHOPHYSIOLOGY

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  • Major characteristics:

    • Airflow obstruction (related to bronchospasm, edema, and hypersecretion)

    • Bronchial hyperresponsiveness (BHR)

    • Airway inflammation.

  • Inhaled allergen causes activation of B lymphocytes, mast cells, and macrophages, which release proinflammatory mediators such as histamine and eicosanoids that induce contraction of airway smooth muscle, mucus secretion, vasodilation, exudation, and edema with reduced mucus clearance.

  • Activation of eosinophils, T lymphocytes, basophils, neutrophils, and macrophages cause further release of inflammatory mediators such as leukotrienes, interleukins, histamine, platelet-activating factor (PAF), and chemotactic factors.

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EPIDEMIOLOGY

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  • Affects 25.7 million persons in the United States.

  • Most common chronic childhood disease, affecting approximately 7 million children.

  • Accounts for 1.6% of ambulatory care visits (10.6 million physician office visits and 1.2 million hospital outpatient visits).

  • Resulted in 479,000 hospitalizations and 2.1 million emergency department (ED) visits in 2009.

  • Accounts for >14.4 million missed school days per year.

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RISK FACTORS

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  • Genetic predisposition.

  • Socioeconomic status.

  • Family size.

  • Exposure to secondhand tobacco smoke in infancy and in utero.

  • Allergen exposure.

  • Ambient air pollution.

  • Urbanization.

  • Respiratory syncytial virus (RSV) and rhinovirus infection.

  • Decreased exposure to common childhood infectious agents.

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CLINICAL PRESENTATION

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SIGNS AND SYMPTOMS
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  • Chronic asthma.

    • Symptoms: Episodic dyspnea with wheezing, chest tightness, and coughing that may occur spontaneously, with exercise, or after exposure to known allergens.

    • Signs: Expiratory wheezing; dry, hacking cough; atopy (eg, allergic rhinitis, eczema)

    • Can vary in frequency from intermittent to chronic daily symptoms.

    • Severity determined by lung function, symptoms, nighttime awakenings, and interference with normal activity.

  • Acute severe asthma.

    • Symptoms: Anxiousness with acute distress and complaints of severe dyspnea, shortness of breath, and chest tightness unresponsive to usual measures.

    • Signs: Expiratory and inspiratory wheezing; dry, hacking cough; tachypnea; tachycardia; pallor or cyanosis; hyperinflated chest with intercostal and supraclavicular retractions.

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DIAGNOSIS

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MEANS OF CONFIRMATION AND DIAGNOSIS
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  • Chronic asthma.

    • History of recurrent episodes of coughing, wheezing, chest tightness, or shortness of breath and confirmatory spirometry.

    • May be family history of allergy or asthma, or patient symptoms of allergic rhinitis.

    • History of exercise or cold air precipitating symptoms during specific allergen seasons.

  • Acute severe asthma.

    • History of previous asthma exacerbations (eg, hospitalizations, intubations) and complicating illnesses (eg, cardiac disease, diabetes).

    • Assess hydration status; use of accessory muscles of respiration; and presence of cyanosis, pneumonia, pneumothorax, pneumomediastinum, and upper airway obstruction.

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