Asthma

– A chronic obstructive disorder of the airways characterized by airway hypersensitivity to a variety of stimuli, resulting in transient bronchospasm and constriction of the airways.

Causes and Incidence

Asthma is triggered by either extrinsic or intrinsic agents. Extrinsic agents include allergens such as dust, smoke, pet dander, mold spores, chemicals, and foods. Intrinsic agents include underlying respiratory infections, emotional stress, and fatigue. Many attacks are triggered by a combination of agents. Asthma affects about 3% of the U.S. population and has a death rate of 1 in 100,000. It is the most common chronic disease of children and adults, starting in childhood about half the time and in adolescence or adulthood half the time. In children, boys are affected twice as often as girls, but this ratio evens out by adolescence. The prevalence and mortality rate are increasing worldwide; prevalence rose about 30% from 1980 to 1990.

Disease Process

Various agents trigger a reaction in the tracheal and bronchial linings, which causes bronchospasm of the smooth muscle and constricts the airways. The airways become inflamed and edematous and produce excess thickened secretions, which aggravate the blockage. Eosinophils infiltrate the airway walls, injuring and desquamating the epithelial lining. Expiratory capacity is reduced, causing trapping of gas in the airways, hyperinflation, and labored breathing. Because the obstruction is not uniform, blood flow continues in some areas of hypoventilation, producing a ventilation-perfusion imbalance and resulting in arterial hypoxemia.

Symptoms

Symptoms vary from mild to pronounced, depending on the acuteness and severity of the attack.

Mild
Diffuse wheezing, slight dyspnea, chest tightness.

Moderate
Marked wheezing; dyspnea at rest; hyperpnea; chest tightness; nostril flaring; dry cough; upright, forwardleaning posture; prolonged expiration.

Severe
Decreased wheezing; severe dyspnea; chest retractions; nasal flaring; shallow, rapid respirations; anxiety; fatigue; inability to speak more than a few words before stopping for breath; upright posture; cyanosis.

Potential Complications

Atelectasis, pneumothorax, and status asthmaticus with respiratory failure are common complications.

Diagnostic Tests

The following tests are done for acute attacks. The individual is also assessed for severity of disease based on frequency and severity of attacks, response to bronchodilators, degree of lung damage seen on x-ray, and exercise tolerance.

Clinical evaluation
Abovementioned manifestations plus pulsus paradoxus; decrease in airway exchange, rhonchi, wheezes; increased pulse and respirations.

Arterial blood gases
Mild: pH, PaO2, PaCO2 normal; forced vital capacity (FVC) 80% of normal Moderate: pH increased; PaO2, PaCO2 decreased; FVC 50% of normal Severe: pH, PaO2 decreased; PaCO2 increased; FVC 25% of normal.

Sputum
Increased viscosity, plugs.

Complete blood count
Increased Hct, eosinophilia.

Radiology
Chest xray: normal to hyperinflation; increase in lung markings; possible atelectasis.

Pulmonary function
Total lung capacity, functional reserve capacity, respiratory volume increased; vital capacity normal or decreased.

Treatments

Surgery – None.

Drugs
Acute attack: bronchodilators (aerosol, parenteral); corticosteroids (oral, parenteral) Maintenance: bronchodilators (oral, aerosol); corticosteroids (aerosol); cromolyn sodium; allergy injections.

General
Acute attack: oxygen, fluid and electrolyte replacement; maintain patency of airway Maintenance: avoid triggering agents; flu shots; avoid or obtain early treatment of respiratory infections; education about disease, long-term drug therapy; support groups.