Bronchiolitis

Bronchiolitis (from Latin bronchiolus — small bronchus and the suffix -itis, indicating inflammation) is an acute viral disease of the lower respiratory tract primarily affecting small bronchi and bronchioles in children under 2 years old, characterized by a cough, wheezing, and respiratory insufficiency.

Bronchioles are terminal branches of the respiratory tree (measuring less than 2 mm in diameter) without a cartilaginous framework and ciliated epithelium, directly transitioning into the alveoli.

Etiology and pathophysiology

In the overwhelming majority of cases (up to 80%), the etiological agent is the respiratory syncytial virus (RSV), less frequently – rhinoviruses, adenoviruses, or parainfluenza viruses. The infection has a tropism for the epithelium of the bronchi and bronchioles.

The pathogenesis of the disease is influenced by the anatomical features of young children. The development of the pathology occurs in several stages:

1. viral invasion — triggers a powerful local inflammatory reaction, necrosis, and desquamation of the epithelium;
2. development of inflammation — accompanied by the release of pro-inflammatory cytokines, edema, and mucus hypersecretion;
3. formation of obstruction — leads to partial occlusion of the bronchioles, most pronounced during expiration.

Clinical significance

The peak incidence occurs in children in their first year of life. Due to partial occlusion of the airways, a valve mechanism of obstruction arises: air passes into the alveoli on inspiration but becomes “trapped” on expiration. In cases of complete obstruction of the lumens of the affected areas of the respiratory tract, the development of atelectasis is possible.

Clinically, bronchiolitis manifests after a mild catarrhal prodrome. The child’s condition deteriorates sharply, and the following symptoms appear:

• wheezing (wheezing respiration);
• tachypnea;
• use of accessory muscles — manifested by the retraction of compliant areas of the chest.

Due to the viral etiology, antibacterial therapy is not indicated. Treatment is supportive and includes adequate rehydration and oxygen therapy.