Asthma

SOURCE

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.

DEFINITION

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

ETIOLOGY

• Genetic factors.

• Environmental exposures (see Risk Factors)

PATHOPHYSIOLOGY

• 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.

EPIDEMIOLOGY

• 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.

RISK FACTORS

• 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.

CLINICAL PRESENTATION

SIGNS AND SYMPTOMS

• 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.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

• 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, ...