Asthma

Asthma is a chronic reactive airway disorder that involves episodic, reversible airway obstruction resulting from bronchospasms, increased mucus secretions, and mucosal edema. Signs and symptoms range from mild wheezing and dyspnea to life-threatening respiratory failure. Signs and symptoms of bronchial airway obstruction mayor may not persist between acute episodes.

This common respiratory condition can strike at any age, but about half of all patients with asthma are under age 10. In this age group, asthma affects twice as many boys as girls. About one-third of patients experience asthma onset between ages 10 and 30. In this group, incidence is the same in both sexes. Hereditary factors are also important: About one-third of all patients with asthma share the disease with at least one immediate family member.

Asthma may result from sensitivity to specific external allergens (extrinsic) or from internal, nonallergenic factors (intrinsic). Allergens that cause extrinsic asthma (atopic asthma) include pollen, animal dander, house dust or mold, kapok or feather pillows, food additives containing sulfites. and any other sensitizing substance. Extrinsic asthma begins in children and is commonly accompanied by other manifestations of atopy (type I, immunoglobulin E [IgE]-mediated allergy), such as eczema and allergic rhinitis.

In intrinsic asthma (nonatopic asthma), no extrinsic substance can be identified. Most episodes are preceded by a severe respiratory tract infection (especially in adults). Irritants, emotional stress, fatigue, endocrine changes, temperature and humidity variations, and exposure to noxious fumes may aggravate intrinsic asthma attacks. In many asthmatics, especially children, intrinsic and extrinsic asthma coexist.

Causes and pathophysiology

Asthma is probably due to a combination of environmental and genetic factors. You're more likely to develop asthma if it runs in your family and if you're sensitive to environmental allergens or irritants. Early, frequent infections and chronic exposure to secondhand smoke or certain allergens may increase your chances of developing asthma.

Exposure to various allergens and irritants may trigger your asthma symptoms. The following are common things that trigger asthma symptoms:

• Allergens, such as pollen, animal dander or mold
• Cockroaches and dust mites
• Air pollutants and irritants
• Smoke
• Strong odors or scented products or chemicals
• Respiratory infections, including the common cold
• Physical exertion, including exercise
• Strong emotions and stress
• Cold air

Signs and Symptoms

Common symptoms of an asthma flare-up are coughing, feeling breathless, a feeling of tightness in the chest and wheezing (breathing that makes a hoarse, squeaky, musical or whistling sound). Watch yourself every day for any of these symptoms.

Diagnostic tests

Pulmonary function studies reveal signs of airway obstructive disease (decreased flow rates and forced expiratory volume in 1 second [FEV1 ] , low-normal or decreased vital capacity, and increased total lung and residual capacities. Despite abnormal findings during asthmatic episodes, pulmonary function may be normal between attacks.

Typically, the patient has decreased partial pressure of arterial oxygen (pao2) and partial pressure of arterial carbon dioxide (Paco2). However, in severe asthma, Paco2 may be normal or increased, indicating severe bronchial obstruction. In fact, FEV1 is most likely less than 25% of the predicted value. Initiating treatment tends to improve the airflow. However, even when the asthma attack appears controlled, the spirometric values (FEV1 and forced expiratory flow between 25% and 75% of vital capacity) remain abnormal, necessitating frequent arterial blood gas (ABG) analyses or pulse oximetry measurements. Residual volume remains abnormal for up to 3 weeks after the attack.

Serum IgE levels may increase from an allergic reaction, and complete blood count with differential reveals increased eosinophil count.

Chest X-rays can be used to diagnose or monitor the progress of asthma. X-rays may show hyperinflation with areas of focal atelectasis.

ABG analysis is used to detect hypoxemia and guides treatment.

Skin testing may be used to identify specific allergens. Test results are ready in 1 to 2 days to detect an early reaction and then again after 4 or 5 days to reveal a late reaction.

Bronchial challenge testing is used to evaluate the clinical significance of allergens identified by skin testing.

Treatment

The best treatment for asthma is prevention by identifying and avoiding precipitating factors, such as environmental allergens or irritants. Usually, such stimulants can't be removed entirely. Desensitization to specific antigens may be more helpful in children than in adults with bronchial asthma.

Drug therapy, which usually includes bronchodilators, is most effective when begun soon after the onset of signs and symptoms. Bronchodilators used include rapid-acting epinephrine, methylxanthines (theophylline and aminophylline), and beta2­adrenergic antagonists (albuterol and terbutaline) for the effect of decreasing bronchoconstriction. Corticosteroids (hydrocortisone sodium succinate, prednisone, methylprednisolones, and beclomethasone) are used for their anti-inflammatory and immunosuppressant effects), which decrease inflammation and edema of the airways. Cromolyn and nedocromil help prevent the release of the chemical mediators (histamine and leukotrienes) that cause bronchoconstriction. Anticholinergic bronchodilators (such as ipratropium) block acetylcholine, another chemical mediator. ABG measurements help to determine the severity of an asthma attack and the patient's response to treatment. For the most part, medical treatment of asthma must be tailored to the patient.

In addition, low-flow oxygen may be required, as may antibiotics if infection exists. Fluid replacement may also be needed.

Status asthmaticus must be treated promptly to prevent progression to fatal respiratory failure. The patient with increasingly severe asthma that doesn't respond to drug therapy is usually admitted to the intensive care unit for treatment with corticosteroids, epinephrine, sympathomimetic aerosol sprays, and I. V aminophylline. He needs frequent ABG analysis and pulse oximetry to assess respiratory status, especially after ventilator therapy or a change in oxygen concentration. The patient may require endotracheal intubation and mechanical ventilation if his Paco2 increases.

Prevention

• If your asthma attacks are triggered by an allergic reaction, avoid your triggers as much as possible.
• Keep taking your asthma medications after you are discharged. This is extremely important. Although the symptoms of an acute asthma attack go away after appropriate treatment, asthma itself never goes away.