What is bronchopulmonary dysplasia (BPD) in premature infants?

Definition of Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of prematurity defined by the need for supplemental oxygen for at least 28 days after birth, with severity graded based on respiratory support requirements at 36 weeks postmenstrual age. 1

Core Diagnostic Criteria

The most widely accepted definition includes three essential components 1:

• Oxygen requirement for ≥28 days of postnatal life - This remains the fundamental criterion, though its application varies by gestational age 1
• Clinical signs of respiratory compromise persisting beyond 28 days - Including tachypnea, retractions, or rales 1
• History of positive-pressure ventilation during the first 2 weeks of life (minimum 3 days) with characteristic chest radiograph findings 1

Severity Classification

The National Institute of Child Health and Human Development/National Heart, Lung, and Blood Institute workshop refined BPD definitions to reflect different criteria based on gestational age at birth 1:

• For infants <32 weeks gestation: Severity is determined by oxygen and ventilatory requirements at 36 weeks postmenstrual age 1
• For infants ≥32 weeks gestation: Different thresholds apply, with assessment at 56 days postnatal age or discharge (whichever comes first) 1

The severity grading distinguishes between 1:

• Mild BPD: Breathing room air at 36 weeks postmenstrual age
• Moderate BPD: Requiring <30% FiO₂ at 36 weeks postmenstrual age
• Severe BPD: Requiring ≥30% FiO₂ and/or positive-pressure ventilation at 36 weeks postmenstrual age

Evolution of Diagnostic Criteria

A critical distinction exists between "old" and "new" BPD, as modern cases predominantly affect extremely premature infants born during the canalicular or early saccular period of lung development 1, 2:

• Classic BPD (1967): Originally described in infants with mean gestational age of 34 weeks, characterized by barotrauma and oxygen toxicity causing fibrosis and emphysematous changes 2
• New BPD (current): Primarily affects infants <28 weeks gestation, representing arrested lung development rather than injury-induced scarring 2, 3

Alternative Diagnostic Approaches

The 36-week postmenstrual age criterion has gained favor over the 28-day postnatal age definition for very low birth weight infants 1:

• Shennan and colleagues demonstrated that oxygen dependence at 36 weeks postmenstrual age more accurately predicts long-term pulmonary outcomes in extremely premature infants (≤30 weeks gestation) 1
• However, oxygen dependence at 28 days remains useful for predicting subsequent respiratory morbidity in some populations 1

Broader Context: Post-Prematurity Respiratory Disease

The term "post-prematurity respiratory disease" (PPRD) encompasses a wider spectrum than BPD alone, including premature infants who develop respiratory sequelae without meeting strict BPD criteria 1:

• Premature infants not meeting BPD definitions may still develop chronic cough, recurrent wheezing, exercise intolerance, hypoxemia, and reduced pulmonary function later in life 1
• This broader terminology reflects that disrupted lung development from prematurity causes lifelong respiratory consequences, including increased risk of chronic obstructive pulmonary disease 1

Common Diagnostic Pitfalls

The definition has been questioned because many infants requiring oxygen at 28 days no longer require prolonged mechanical ventilation or show characteristic radiographic changes 1:

• Simple oxygen requirement at 28 days in infants with birth weights ≤1,500 g has been proposed as a simplified criterion 1
• Non-standardized application of oxygen therapy across institutions creates inconsistency in diagnosis 2
• Treatment-based definitions (oxygen use) rather than pathophysiological assessments limit prognostic utility 2

Incidence and Risk Factors

BPD develops in approximately 45% of extremely preterm infants, with highest incidence in those with birth weights <1,000 g 1, 2:

• The condition most commonly evolves from respiratory distress syndrome in premature infants 1, 3
• Any acute lung injury requiring positive-pressure ventilation and high oxygen concentrations during initial weeks of life predisposes to BPD 1
• Other precipitating conditions include pneumonia/sepsis, meconium aspiration, pulmonary hypoplasia, and persistent pulmonary hypertension 1