asthma

asthma is a topic covered in the Taber's Medical Dictionary.

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(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), adj.

INCIDENCE
Between 8% and 9.5% of Americans have asthma.

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 demands 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).

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