Chapter 33: Drug Therapy for Asthma, Airway Inflammation, and Bronchoconstriction

Characteristics of Bronchoconstrictive Disorders

Bronchoconstrictive disorders are respiratory conditions characterized by narrowing of the airways, leading to impaired airflow and breathing difficulties. Common features include:

• Airway inflammation: Swelling and irritation of the airway lining.

• Bronchoconstriction: Contraction of bronchial smooth muscle, reducing airway diameter.

• Airway hyperresponsiveness: Increased sensitivity to stimuli, causing exaggerated bronchoconstriction.

• Mucosal edema: Swelling of the mucous membrane lining the airways.

• Excessive mucous production: Increased secretion of mucus, further obstructing airflow.

Examples of bronchoconstrictive disorders include asthma, chronic bronchitis, and emphysema.

Asthma

Overview and Pathophysiology

Asthma is a chronic respiratory disorder with unknown exact cause, but it is believed to result from a combination of genetic and environmental factors. It is characterized by:

• Bronchoconstriction and airway inflammation

• Airway hyperresponsiveness to various stimuli

• Symptoms: Chronic cough, dyspnea (shortness of breath), wheezing, chest tightness, and increased mucous production

• GERD association: Gastroesophageal reflux disease may exacerbate asthma symptoms

Pathophysiology involves narrowing of airways due to bronchoconstriction, which can be aggravated by inflammation, mucosal edema, and excessive mucus. Mast cells release substances in response to triggers, leading to further bronchoconstriction and inflammation.

Asthma Across Age Groups

• Asthma can occur at any age, though it is especially common in children.

• Children exposed to allergens and irritants (e.g., tobacco smoke) during infancy are at higher risk.

Chronic Obstructive Pulmonary Disease (COPD)

Definition and Features

Chronic Obstructive Pulmonary Disease (COPD) encompasses chronic bronchitis and emphysema. It usually develops after prolonged exposure to airway irritants, such as cigarette smoke. Key features include:

• Symptoms are more constant and less reversible compared to asthma.

• Long-standing exposure to irritants is a major risk factor.

Drug Therapy for Asthma and Bronchoconstriction

Beta2-Adrenergic Agonists

Beta2-adrenergic agonists are bronchodilators administered by inhalation, which is the most effective and preferred method for acute asthma relief. There are two main types:

• Rescue inhalant medications: Short-acting drugs used during acute symptoms and exacerbations.

• Maintenance inhalant medications: Long-term control drugs for prophylactic management of persistent asthma.

Adrenergics (e.g., Albuterol)

• Mechanism: Stimulate beta2-adrenergic receptors in bronchial smooth muscle, activating adenyl cyclase and increasing cyclic AMP, resulting in bronchodilation.

• Administration: Metered-dose inhaler (MDI) is preferred for fewer systemic effects.

• Adverse effects: Muscle tremor (most frequent), cardiac stimulation (angina, tachycardia, palpitations), CNS stimulation (agitation, anxiety, insomnia, seizures, tremors), serious dysrhythmias, and cardiac arrest.

Example: Albuterol is used for acute asthma attacks as a rescue medication.

Anticholinergics

Anticholinergic bronchodilators, such as ipratropium, block the action of acetylcholine in bronchial smooth muscle, reducing bronchoconstriction.

• Adverse effects: Cough, nervousness, nausea, gastrointestinal upset, headache, dizziness (vary by medication).

Anti-inflammatory Agents

Corticosteroids (e.g., Beclomethasone)

• Used for: Acute and chronic asthma, other bronchoconstrictive disorders.

• Effects: Decrease mucous secretion, reduce airway mucosa edema, repair epithelial damage, and reduce airway reactivity.

Leukotriene Modifiers (e.g., Montelukast)

• Used for: Long-term treatment of asthma.

• Prevent: Acute asthma attacks induced by allergens, exercise, cold air, hyperventilation, irritants, NSAIDs.

• Not effective: For relief of acute attacks.

Immunosuppressant Monoclonal Antibodies (e.g., Omalizumab)

• Mechanism: Bind to target cells or proteins to modulate the immune system.

Adjuvant Medications

Mast Cell Stabilizers (e.g., Cromolyn)

• Prevent: Release of bronchoconstrictive and inflammatory substances in response to allergens and other stimuli.

• Used for: Prophylaxis of acute asthma in mild, persistent cases.

• Not effective: In acute bronchospasm or status asthmaticus.

Combination Regimens

• Allow smaller doses of each agent, decreasing adverse effects.

• Permit dosage increases during symptom exacerbation.

Clinical Considerations and Nursing Process

Implementation Strategies

• Prevent or relieve bronchoconstriction: Use general measures to prevent respiratory disease and promote airway adequacy.

• Monitoring: Implement specific plans, such as peak-flow or symptom monitoring.

• Mechanical measures: Remove excessive respiratory tract secretions via coughing, deep breathing, percussion, and postural drainage.

• Patient education: Help patients identify and avoid triggers, recognize early signs of difficulty, and understand medication use.

• PEFR monitoring: Assist patients in measuring Peak Expiratory Flow Rate (PEFR) and develop action plans for acute attacks.

• Anxiety reduction: Prevent or reduce anxiety, which can worsen bronchospasm.

• Smoking cessation: Encourage and support patients who smoke to quit.

Key Clinical Questions

Asthma in Children

• Statement: Asthma occurs only in children.

• Answer: False. Asthma may occur at any age, though it is especially common in children.

Corticosteroid Use in Acute Severe Asthma

• Statement: In acute, severe asthma, a topical corticosteroid (in relatively high doses) is indicated for a patient whose respiratory distress is not relieved by an inhaled beta2-agonist.

• Answer: False. In acute, severe asthma, a systemic corticosteroid (in relatively high doses) is indicated. Topical corticosteroids are not effective against airway inflammation.

Summary Table: Drug Classes for Asthma and Bronchoconstriction

Key Formula: Cyclic AMP Production

Beta2-adrenergic agonists stimulate the enzyme adenyl cyclase, increasing production of cyclic AMP, which leads to bronchodilation:

Additional info: cAMP (cyclic adenosine monophosphate) is a second messenger important in many biological processes, including smooth muscle relaxation in the airways.