asthma
(az'mă 
)
[Gr. asthma, panting, shortness of breath]
An inflammatory disorder of the airways that causes periodic and reversible obstruction to airflow, usually in response to an allergen, a chemical irritant, an infection, or physical stimuli such as cold air or exercise.
asthmatic,
(az-mat'ik )
Incidence and Prevalence: Approx. 26 million Americans have asthma. African-Americans, women, and the elderly are disproportionately affected by the disease.
Causes: The recurrence and severity of attacks are influenced by several triggers. Exposure to tobacco smoke and viral illnesses are the most frequently identified factors. Other respiratory exposures, e.g., to air pollution, allergens, dust, cold air, exercise, fumes, or medicines, may contribute to asthma attacks. Autonomic and inflammatory mediators (esp. arachidonic acid derivatives such as leukotrienes) play important roles.
Symptoms and Signs: Clinically, most patients present with episodic wheezing, shortness of breath, and /or cough. Between attacks the patient may or may not have normal respiratory function. Although most asthmatics have mild disease, in some cases the attacks become continuous. This condition (status asthmaticus) may be fatal.
Diagnosis: Asthma is readily diagnosed clinically during attacks, during which the patient, typically a child or adolescent, develops shortness of breath, cough and wheezing after exposure to smoke, an inhaled allergen, or a respiratory infection. Between attacks, asthma may be diagnosed with spirometry as a decrease in the amount of air a person can exhale in one second during a maximal exhalation (the FEV1) and as a decrease in the total forced expiratory volume divided by the forced vital capacity (the FEV1/FVC ratio). These deficits reverse by at least 12% after the administration of beta-agonist drugs like albuterol. When the diagnosis is uncertain, it can be determined with the use of a methacoline challenge, a test in which a provocative concentration of this muscarinic agonist is given to the patient to inhale and airway responsiveness is measured.
Treatment: Mild episodic asthma is well managed with intermittent use of short-acting inhaled beta-2 agonists, such as levalbuterol. Patients with more severe disease or frequent exacerbations rely on other medications to control the disease, such as inhaled corticosteroids, mast cell stabilizing drugs, e.g., cromolyn, long-acting beta-2 agonists (e.g., salmeterol), inhibitors of leukotrienes (e.g., montelukast), and short-acting beta-2 agonists. IgE blockade with omalizumab, a monoclonal antibody, may be used for severe allergic asthma; its routine use is limited by its cost. Salmeterol and formoterol, both long-acting beta-2 agonists, have been linked to an increased risk of death and carry a black box warning.
Acute asthmatic attacks may require high doses or frequent dosing of beta-agonists and steroids. Supplemental oxygen is provided. Increased fluid intake is encouraged to help thin secretions and ease their removal. Antibiotics are used only for bacterial infection. The patient is observed closely to see how well he or she adapts to the demand s imposed by airway obstruction. Key elements of the patient's response are a subjective sense of breathlessness, fatigue during breathing, and whether the attack is worsening or improving with treatment. Monitoring of the acute asthmatic patient includes regular assessments of peak air flow, oxygen saturation, blood gases, and cardiac rhythms. Exhaustion or altered mental status may be signs of impending respiratory failure, which may warrant close noninvasive ventilatory support or endotracheal intubation.
Patient Care: When the acute attack subsides, the nurse or respiratory therapist instructs the patient in the proper use of inhaled medications, paying special attention to how well the patient uses metered dose inhalers. A spacer device is often used to improve the inhalation of medications into the lower airways.
Patients whose breathing is labored are seated in an upright (high-Fowler) position to ease ventilatory effort and are given low-flow oxygen and other prescribed medications. Purulent sputum should be sent to the laboratory for culture and sensitivity, Gram stain, or other ordered studies. The health care provider educates the patient about eliminating exposure to allergens or irritants, e.g., secondhand smoke, cold air, and teaches home measures to prevent or decrease the severity of future attacks. Caregivers ascertain that patient and family understand the prescribed maintenance regimen, including the reasons for the order in which inhalers are to be used and any adverse effects to be reported, as well as the use of emergency treatment if an attack threatens.
Further information on asthma and this and other tests can be obtained from the National Heart, Lung, and Blood Institute (www.nhlbi.nih.gov); National Asthma Education and Prevention Program (https://www.nhlbi.nih.gov/about/org/naepp); and the American Lung Association (http://www.lungusa.org).
adult-onset a.Asthma that begins after age 16, typically as a result of exposure to environmental pollution, occupational antigens, or tobacco smoke.
SEE: bronchiolitis.
bakers' a.A colloquial term for asthma caused by inhalation of airborne wheat proteins in occupational settings.
bronchial a.A common form of asthma due to hypersensitivity to an allergen. SYN: allergic asthma.
cardiac a.Asthma that results from heart disease, esp. acute or chronic heart failure.
ABBR: e-asthma
Asthma in which elevated levels of eosinophils are found in the airways. Eosinophils can inflame and injure airways and increase the severity of the illness.exercise-induced a.Asthma that occurs during physical exertion.
extrinsic a.Asthma triggered by an allergic (hypersensitivity) response to an antigen.
intrinsic a.Asthma assumed to be due to some endogenous cause because no external cause can be found.
irritant-induced a.Asthma due to exposure to substances that inflame the airways or make them hyperreactive but without inducing an allergic reaction.
nocturnal a.An increase in asthmatic symptoms during sleep. Nocturnal asthma may be caused by a variety of conditions, including gastroesophageal reflux, allergens in the bedroom, circadian variations in circulating hormone levels, or inadequate doses of anti-asthmatic medications at night. Treatment is tailored to the underlying cause.
occupational a.Asthma resulting from exposures in the workplace to environmental dusts, fibers, gases, smoke, sprays, or vapors.
stable a.Asthma in which there has been no increase in symptoms or need for additional medication for at least the past 4 weeks.
unstable a.An increase in asthmatic symptoms during the past 4 weeks.
Usually the dosage of the patient's bronchodilator or other medications needs to be increased.
The patient must be monitored closely for signs of respiratory failure such as abnormal sensorium and severe tachypnea and tachycardia.