Bronchiolitis

Definition

  • Bronchiolitis is a clinical syndrome of infection and associated inflammation of the lower respiratory tract that generally occurs in children less than 2 years of age. It is usually associated with a viral pathogen and can be associated with wheezing and/or rales. 

Pathophysiology

  • Viral infection of terminal bronchiolar epithelial cells
  • Edema, mucus formation, sloughing of epithelial cells with subsequent obstruction of small airways and atelectasis
  • Most common cause is RSV (late fall/winter), followed by rhinovirus (spring/fall). Other causes include human metapneumovirus, influenza, adenovirus, and coronavirus. Approximately 1/3 of patients have infection with 2 or more viruses.1

Risk factors for Severe Disease

  • Prematurity 
  • Age <12 weeks
  • Chronic pulmonary disease
  • Congenital/anatomic defects of the airways
  • Congenital heart disease
  • Immunodeficiency
  • Passive smoking
  • Daycare attendance

Clinical Features

  • URI symptoms with presentation typically at day 3-6
  • Peak symptoms thought to occur ~day 4-7
  • Tachypnea, retractions, wheezing, rales, mild hypoxemia
  • Hyperexpanded on chest x-ray
  • Comorbid serious infections low (1-2% for bacteremia/meningitis, 5% for UTI) although in intubated infants, frequency of bacterial superinfection is as high as 40%)2,3
  • Apnea ~5% incidence (younger age, prematurity, increased risk of respiratory failure)
  • Respiratory failure in about 15% 
File:RSV.PNG
Figure 1. Peribronchial Cuffing Typical of Bronchiolitis (occlusion of small airways via mucus plugging leads to atelectasis and prominent appearance of bronchioles). 
Another common finding is shifting atelectasis.

Treatment

  • Supportive care 
  • Fluid hydration (ADH levels may be elevated so consider isotonic fluids)
  • Supplemental O2 to maintain SpO2 >90-92% (AAP guidelines of >90% although no specific data)
  • CPAP (4-8) or HFNC of 4-8LPM to reduce work of breathing (flow rates of 6 L/min seem to be associated with delivered PEEP)
  • Antibiotics generally warranted in intubated patients given the 40% risk of bacterial coinfection. In patients on the general care ward, antibiotics would not generally be recommended
  • Chest PT did not improve respiratory parameters, O2 requirement, or length of stay in non-intubated patients4
  • Trial of inhaled bronchodilators (albuterol), if no response, stop
  • Hypertonic saline: Some evidence to suggest decreased risk of hospitalization and length of stay in hospitalized patients (newer RCT evidence-Angoulvant, JAMA PEDS 2017- did not show such an improvement in admission rates)5
  • Steroids generally not recommended unless clear history of previous reactive airway disease
  • Ribavarin generally not recommended unless immunocompromised or severe disease
  • RSV-IVIG and RSV-monoclonal Ab not recommended as no effect on outcomes
  • Possible reduced duration of mechanical ventilation with surfactant although not routinely used6
  • No significant evidence to support the use of heliox
The Bottom Line:
  • Supportive care with HFNC/CPAP/Mechanical ventilation as needed
  • Antibiotics, guided by tracheal aspirate in the intubated population (in general, given ~40% risk of coinfection)
  • Suctioning and PT not particularly helpful in the general inpatient population but may be necessary in the PICU population
  • Trial of albuterol
  • Hypertonic saline frequently utilized (ie q6hrs with albuterol given propensity of HTS to produce bronchospasm)
  • Tincture of time- length of mechanical ventilation and PICU stay can be quite variable

Complications

  • Possible association with the development of asthma but unclear
  • Mortality <2% in developed world

References