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ACUTE BRONCHIOLITIS

DEFINITION:

An acute viral syndrome of the bronchioles characterized by wheezing and respiratory distress.

EPIDEMIOLOGY:

incidence: 10-15/1000 (most common LRI syndrome in young kids)
age of onset:
- less than 2 yrs with peak between 6-10 weeks of age
risk factors:
- winter -> early spring (RSV); fall (M. pneumoniae)
- M > F
- high risk patients:
  - cardiopulmonary disease (CHF, CF, BPD)
  - immunocomprimised
  - trisomy 21

PATHOGENESIS:

1. Pathogens

1. Major (33%)

Respiratory Syncytial Virus (RSV)

2. Minor

adenovirus types 7 & 21
parainflenzae types 1 & 3
influenzae A & B, enterovirus
mycoplasma pneumoniae

2. Pathogenesis

The infecting virus spreads from the upper respiratory tract (prodrome) and invades the medium and small bronchi and bron-chioles resulting in an inflammatory response consisting of edema and exudate (mucous and cellular debris) and epithelial necrosis. Since resistence to the airflow is inversely related to the 4th power of the radius (Poiseuille's Law), even minor thickening of the bronchiolar wall produces a profound effect on airflow. Airway resistence in the smaller air passages increases during both inspiration and expiration but since the radius of the airway is smaller during expiration, the resulting ball-valve respiratory obstruction leads to early air trapping and overinflation. Atelectasis occurs when the obstruction becomes complete and trapped air is absorbed.
RSV is shed from the respiratory tract for an average of 9 days in children under 1 year of age and for up to months in infants with immunodeficiency syndromes.

DIAGNOSIS:

1. Clinical

age, season, clinical features

2. Laboratory

viral (RSV) identification

CLINICAL FEATURES:

1. Prodrome

mild URTI for several (1-4) days:
- rhinitis (serous nasal discharge)
- sneezing
- cough
- fever (38.5-39 C)
- anorexia with poor feeding

2. Respiratory Manifestations

mild cases:
- gradual onset and resolves within 1-3 days
- paroxysmal wheezing cough
worsening signs:
- sudden onset and protracted
- audible wheezing
- prolonged expiratory phase
- widespread fine end inspiratory, early expiratory crackles
- decreased breath sounds
- tachypnea (60-80 b/min)
- tachycardia (>200 b/min)
- hypoxia +/- cyanosis
- lethergy and apnea
- signs/symptoms of respiratory distress

3. Complications

1. Acute

dehydration
febrile seizures
respiratory distress with prolonged apneic spells
respiratory failure
death (mortality rate <1% but if underlying disease this is >1%)

2. Chronic

1. RSV Bronchiolitis

asthma
- strong association between proven RSV bronchiolitis and subsequent development of asthma - about 30-50% of those with RSV bronchiolitis go on to develop asthma
- may find an increased anti-RSV IgE antibody titre during an acute RSV infection

2. Adenovirus Bronchiolitis

bronchiolitis obliterans (chronic bronchiolitis)
unilateral hyperlucent lung syndrome

4. Prognosis

1. Acute Course

80% of cases will be clinically improved within 3-4 days of initial presentation (recovery usually dramatic)
blood gases normalize over the next 2 weeks
radiologic changes normalize over 9 weeks

2. Prolonged Course

20% of cases will have a protracted course lasting from weeks to months
persistent wheezing and hyperinflation
abnormal gas exchange and lung function
some develop lobar collapse

INVESTIGATIONS:

1. Serum

1. CBC

WBC (5-24), may have increased PMN and bands

2. Blood Gas

hypoxia due to V/Q mismatch
metabolic acidosis (if dehydrated)

3. Others

lytes, BUN, creatinine (dehydration)

2. Imaging Studies

1. Chest X-Ray

scattered areas of consolidation, segmental collapse and/ or patchy atelectasis
hyperinflation - flattened diaphragms with increased AP diameter
peribronchial thickening
rule out CHF, foreign bodies, BPD, bacterial pneumonia

3. Virology

nasopharyngeal aspirate for RSV or other viruses
culture and rapid antigen detection techniques

MANAGEMENT:

depends upon the degree of severity:

1. Mild

noisy breathing with no distress
send home if parents are good and a close distance
instructions:
- sleep in propped up position
- cool mist humidifier
- oral rehydration if dehydrated

2. Moderate

moderate respiratory distress +/- apneic spells or cyanosis
high risk patient
admit to hospital with:
- humidified oxygen
- saturation moniter for hypoxia
- apnea and blood gas monitering
- careful temperature control
- oral/IV rehydration

3. Severe

severe respiratory distress or failure
admit to ICU:
- intubate and ventilate for mean of 5 days
- ribavirin

1. Humidified Oxygen

proposed mechanism of action:
- relieves hypoxia, dyspnea, and cyanosis
- decreases the insensible water loss from tachypnea
dose:
- humidified 35-40% oxygen by mask or hood box

2. Ribavirin (Virazole)

proposed mechanism of action:
- a synthetic antiviral agent directed against viral DNA
- this guanine analog prevents viral replication
effect:
- shortens the clinical course
- reduces the severity of bronchiolitis if administered early in the course of the disease
dose:
- continuous inhalation as a small particle mist for 12-20 hours per 24 hours for 3-5 days
indications:
- see Committee on Infectious Diseases, 1987
- high risk patients

3. Antibiotics

not indicated unless evidence of secondary bacterial infection:
- clinical deterioration +/- sepsis
- tracheal secretions positive on gram stain or C&S
- significant increase in WBC count and left shift

4. Bronchodilators/Steriods

use in Bronchiolitis is controversial
Salbutamol 0.04 cc/kg (up to 1cc) per dose of inhalation solution diluted in 2cc normal saline q4h with q2h prn - continue to use only if effective (i.e., decreased wheezing after a treatment)

5. Experimental

immunotherapy - human IgG against RSV

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