Bronchopulmonary Dysplasia

Overview

Bronchopulmonary Dysplasia (BPD) was classically thought of as a chronic lung disease of children who were born prematurely with low birthweights and who received mechanical ventilation with high pressure and oxygen supplementation to treat respiratory distress syndrome [1].

“Old BPD”

“New BPD”

Before the advent of antenatal corticosteroids and postnatal surfactant therapy.

Since the advent of CPAP, improved ventilators, antenatal corticosteroids, and surfactant.

-Preterm infants with hyaline membrane disease treated with high ventilator pressures and high oxygen concentrations.

- Disease was hallmarked by airway inflammation, fibrosis, and smooth muscle hypertrophy due to barotrauma and volutrauma.

- This has all but disappeared.

-Patholgic finding in surfactant-treated extremely low birth weight (ELBW – less than 1000g) infants is disruption of lung development with decreased septation and alveolar hypoplasia leading to fewer and larger alveoli with reduced surface area for gas exchange [2, 3].

-Pulmonary vasculature is also disrupted, with abnormal distribution of capillaries, reduced total number of capillaries, and thickened muscle layer of pulmonary arterioles leading to increased pulmonary resistance.

Definition of BPD: NICHD Diagnostic Criteria (2001)

As the field of neonatology advances, the definition of BPD continues to evolve. The current definition focuses on the need for supplemental oxygen [4]:

	Gestational age
	<32 week	≥32 week
Time point of assessment	36 weeks PMA or discharge to home, whichever comes first	>28 days but <56 days postnatal age or discharge to home, whichever comes first
	Treatment with oxygen >21 percent for at least 28 days plus
Mild BPD	Breathing room air at 36 weeks PMA or discharge, whichever comes first	Breathing room air by 56 days postnatal age or discharge, whichever comes first
Moderate BPD	Need* for <30 percent oxygen at 36 weeks PMA or discharge, whichever comes first	Need* for <30 percent oxygen at 56 days postnatal age or discharge, whichever comes first
Severe BPD	Need* for ≥30 percent oxygen and/or positive pressure (PPV or NCPAP) at 36 weeks PMA or discharge, whichever comes first	Need* for ≥30 percent oxygen and/or positive pressure (PPV or NCPAP) at 56 days postnatal age or discharge, whichever comes first

Pathogenesis and Risk Factors

Prematurity: Lung is most susceptible to damage in saccular stage of development (23-32 wks GA).
Fetal growth restriction: Increases vulnerability of lungs.
Mechanical ventilation: Large tidal volumes over-distend airways and airspaces.
Oxygen toxicity: High concentrations of inspired O2 cause overproduction of cytotoxic reactive O2 metabolites.
Infection (postnatal): Sepsis increases risk of BPD.
Infection (chorioamnionitis): Previously thought to contribute, but no longer clearly associated.
Genetics: Underlying factors still not known.
Late surfactant deficiency: Transient surfactant dysfunction or deficiency increases risk of BPD.
Patent ductus arteriosus: Seems to increase risk, but not a direct correlation because closing ductus does not decrease risk of BPD.

Clinical Features

Physical Exam	Variable. Usually tachypneic. May have mild to severe retractions, scattered rales, intermittent expiratory wheezing.
Chest Radiograph	Diffusely hazy, reflecting atelectasis, inflammation, pulmonary edema. Increases with increasing severigy. Normal/low lung volumes; severe disease shows hyperinflation. Streaky densities or cystic areas correspond to fibrotic changes.
Cardiopulmonary Function	In severe disease: decreased tidal volume, increased airway resistance, decreased dynamic lung compliance. Hypoxemia and hypercapnia. Increased pulmonary vascular resistance and elevated right atrial pressure.

A radiograph of bronchopulmonary dysplasia https://en.wikipedia.org/wiki/Bronchopulmonary_dysplasia

Outcomes

Mortality	Higher risk of mortality, usually by respiratory failure, unremitting pulmonary hypertension with cor pulmonale, or sepsis [5].
Pulmonary	Increased risk of respiratory infections, including life-threatening RSV [6]. Increased episodes of wheezing related to bronchiolitis or asthma. Persistent abnormalities in pulmonary function. Pulmonary artery hypertension and cor pulmonale.
Neurodevelopmental	Increased risk of abnormal neurologic exam scores on Bayley Scales of Infant Development [7], poorer receptive and expressive language skills [8].
Growth	Poor growth during NICU stay and after hospitalization due to increased energy expenditure of respiratory distress.

Management

Most patients gradually improve as healing and lung growth continues. Management focuses on minimizing further injury, creating a good environment for growth and recovery, and detecting complications of BPD. Close follow-up is recommended.

Respiratory Support	- Mechanical ventilation: small tidal volumes preferred, with maintained PEEP of 5-7 cm H2O to minimize atelectasis. Wean ventilator support as tolerated. - Oxygen: supplemental oxygen may be necessary, but increased concentrations increase risk of retinopathy of prematurity and worsen existing pulmonary disease.
Nutrition	Infants have increased need of 150 kcal/kg/day.
Fluid restriction	Restrict fluid to 140-150 ml/kg/day to avoid pulmonary edema.
Diuretics	May improve pulmonary mechanics, but little evidence on long-term outcome.
Bronchodilators	Inhaled bronchodilators do not affect the clinical course of new BPD and are not recommended long-term. In some infants with severe disease, short-term function may be improved [9].
Corticosteroids	AAP does not recommend routine use of systemic dexamethasone [10].

Postnatal Prevention

Vitamin A	Supplementation in ELBW infants is beneficial.
Caffeine	Helps with apnea of prematurity.
prophylactic surfactant with brief ventilation	Reduces rates of BPD compared with continued mechanical ventilation.

References

Vohr B.R. et al. Neurodevelopmental and Functional Outcomes of Extremely Low Birth Weight Infants in the National Institute of Child Health and Human Development Neonatal Research Network, 1993–1994. Pediatrics, 2000
Singer L.T. et al. Preschool Language Outcomes of Children With History of Bronchopulmonary Dysplasia and Very Low Birth Weight. Journal of Developmental & Behavioral Pediatrics, 2001
Jobe, A.H. and Bancalari E. Bronchopulmonary Dysplasia. American Journal of Respiratory and Critical Care Medicine 2001.
Blackmon L.R. et al. Postnatal Corticosteroids to Treat or Prevent Chronic Lung Disease in Preterm Infants. Pediatrics, 2002. 109(2): p. 330-338.
Baraldi E. and Filippone M. Chronic Lung Disease after Premature Birth. NEJM 2007
Kair L.R. et al. Bronchopulmonary Dysplasia. Pediatrics in Review 2012.
Douglas L. BPD. Pediatrics in Review June 2012