Asthma PDF

Asthma DEFINITION Recurring paroxysms of diffuse wheezing, dyspnea, and cough resulting from inflammation and spasmodic contractions of the bronchi. ETIOLOGY  Asthma is caused by reversible episodes of airway inflammation, mucosal edema, increased viscid secretions, and smooth muscle contractio...

Asthma DEFINITION Recurring paroxysms of diffuse wheezing, dyspnea, and cough resulting from inflammation and spasmodic contractions of the bronchi. ETIOLOGY  Asthma is caused by reversible episodes of airway inflammation, mucosal edema, increased viscid secretions, and smooth muscle contraction. Etiologic categories of asthma include extrinsic asthma, intrinsic asthma, exercise-induced asthma, occupation-induced asthma, drug-induced asthma, cardiac asthma, and triad asthma.  Extrinsic and intrinsic are the two most common forms; both are associated with release of inflammatory chemicals from mast cells in the airways.  Extrinsic asthma makes up one third to one half of all cases of asthma. It commonly affects children and young adults. It is also called allergic asthma because attacks are IgE-mediated responses to specific antigens.  Intrinsic asthma often develops in middle age and has a less favorable prognosis. Respiratory infections may be causative. No allergen can be identified, and it is not IgE mediated. PATHOGENESIS  Asthma is characterized by obstruction and narrowing of airways as a result of bronchospasm, increased mucus secretion, and mucosal edema. With intense narrowing of the bronchi, severe hypoxemia may result.  With extrinsic asthma, IgE is produced in response to a specific antigen. The IgE binds to mast cells, causing them to release inflammatory chemicals (e.g., histamine, leukotrienes) when reexposed to the antigen. CLINICAL MANIFESTATIONS  Common signs and symptoms are wheezing, dyspnea, hyperinflation, productive cough, tachypnea, and tachycardia.  More severe attacks may be accompanied by the use of accessory muscles, intercostal retractions, distant breath sounds, and agitation.  Pulmonary function tests demonstrate decreased forced expiratory volume (FEV1) and peak expiratory flow rate (PEFR). TREATMENT IMPLICATIONS  Prevention of asthma attacks by avoiding triggers is an important part of therapy.  Medications used for prevention and treatment vary with the type of asthma and severity of the attack or symptoms; they include 2-agonists (bronchodilators), mast cell stabilizers (corticosteroids and cromolyn), antihistamines, and leukotriene receptor antagonists.  Peak flow monitoring at home helps determine treatment plans and when to seek medical assistance.