Chapter 35

#### High-Yield Facts

• Bronchiolitis is a self-limited, virally mediated, acute inflammatory disease of the lower respiratory tract, resulting in obstruction of the small airways that occurs almost exclusively in infants.

• It is a clinical diagnosis characterized by rapid respiration, chest retractions and wheezing, and, frequently, hypoxia.

• Respiratory failure may occur secondary to respiratory muscle fatigue or apnea, especially in very young and premature infants.

• Treatment is largely supportive. Routine treatment with bronchodilators or corticosteroids has not been shown to be of benefit.

• Indications for hospital admission include need for supportive care (oxygen or IV fluids), persistent respiratory distress or respiratory failure, adjusted age <6 weeks, or significant underlying disease.

Bronchiolitis is an acute inflammatory disease of the lower respiratory tract that is characterized by acute inflammation, edema, and necrosis of epithelial cells lining small airways, increased mucous production, and bronchospasm.1 The term describes a clinical syndrome that occurs in infancy and is characterized by rapid respiration, chest retractions, wheezing, and, frequently, hypoxia. It is a disease that occurs almost exclusively in children younger than 2 years. It is the leading cause of hospitalization in infancy in the United States, accounting for 3% of all hospitalizations. This results in nearly 150,000 hospital admissions per year with an associated annual cost over $500 million.2 There is evidence that hospitalization rates are increasing as well. It has a seasonal pattern, being most common in the winter and spring.3 #### Etiology The most common etiologic agent in bronchiolitis is respiratory syncytial virus (RSV) which is responsible for 70% of all bronchiolitis cases and even higher in winter months.4 Nearly all children are RSV seropositive by the age of 2. Infection with RSV does not grant permanent or long-term immunity; reinfections are common throughout life.5 Numerous other viruses have been implicated in bronchiolitis. This includes rhinovirus, human bocavirus, metapneumovirus, enterovirus, coronavirus, parainfluenza, adenovirus, influenza, mumps, picornavirus, and echovirus. Adenovirus causes a severe form of the disease. These viruses may also be associated with varying severity of disease and seasonality from the more typical RSV bronchiolitis.69 Mycoplasma pneumoniae and Chlamydia trachomatis also have been associated with bronchiolitis. The principal agent in school-aged children with bronchiolitis is Mycoplasma. #### Pathophysiology Infection produces inflammation of the bronchiolar epithelium, causing necrosis, sloughing, and luminal obstruction. Ciliated epithelium that has sloughed is replaced by cuboidal cells without cilia. The absence of ciliated epithelium prevents adequate mobilization of secretions and debris. The bronchioles and small bronchi are obstructed by submucosal edema, peribronchiolar cellular infiltrate, mucous plugging, and intraluminal debris. The obstruction is not uniform throughout the lungs, leading to ventilation/perfusion mismatching, resultant hypoxia, and compensatory hyperventilation. If the obstruction is severe, hypercapnia may occur. Distal to the obstructed bronchiole, air trapping or atelectasis may occur. The epithelium usually regenerates from the basal layer within 3 to 4 days. However, functional regeneration of the ciliated epithelium usually requires ... ### MyAccess Sign In Username Password Want remote access to your institution's subscription? Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access. Ok ### About MyAccess If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus. ## Subscription Options ### AccessPediatrics Full Site: One-Year Subscription Connect to the full suite of AccessPediatrics content and resources including 20+ textbooks such as Rudolph’s Pediatrics and The Pediatric Practice series, high-quality procedural videos, images, and animations, interactive board review, an integrated pediatric drug database, and more.$595 USD

24 Hour Subscription $34.95 Buy Now 48 Hour Subscription$54.95