Chapter 29

### EPIDEMIOLOGY

Chronic lung disease (CLD) of the newborn, also known as bronchopulmonary dysplasia (BPD), is the most common CLD in early infancy.1 The incidence of BPD varies between newborn care centers, reflecting differences in patient population and infant management practices.2, 3, and 4 Recent publications reported a BPD incidence of 68% in very low birth weight (401- to 1500-g) infants born prior to 29 weeks’ gestation or 77% in infants born at less than 32 weeks’ gestation with a birth weight below 1 kg.3,5,6 The latest studies in Europe reported a BPD rate of up to 25% in infants below 32 weeks’ gestational age (GA).2 The overall incidence in the United States is approximately 10–15,000 cases per year.7 The incidence of BPD is inversely related to GA, varying from 80% or more among the most immature infants at 24 weeks’ gestation to less than 5% among infants greater than 32 weeks’ gestation.2,3,8 Infants who are born very prematurely often require prolonged assisted ventilation to treat acute respiratory failure caused by primary surfactant deficiency (ie, respiratory distress syndrome, RDS), sustained or recurrent apnea, or infections. BPD also can develop in term infants who are treated with long-term mechanical ventilation for respiratory failure from meconium aspiration, bacterial or viral pneumonia, lung hypoplasia, or cardiopulmonary malformations.

Although the rate of severe BPD was found to decrease between 1994 and 2002, the overall incidence did not change.7 The incidence of long-term sequelae remained unchanged or increased among the most immature infants,9 presumably because of a significant reduction of mortality rates.

### PATHOPHYSIOLOGY

#### Definitions

Bronchopulmonary dysplasia, as a pulmonary disease following mechanical ventilation of hyaline membrane disease, was first described 1967 by Northway et al.10 In 1989, the Bureau of Maternal and Child Health and Resources Development proposed the following diagnostic criteria for BPD: (1) Requirement for positive pressure ventilation during the first 2 weeks of life, (2) minimum requirement of ventilation for 3 days, (3) clinical signs of respiratory compromise persisting beyond 28 days of age, (4) requirement for supplemental oxygen beyond 28 days of age to maintain a PaO2 of greater than 50 torr, and (5) chest radiographs showing characteristic lung abnormalities (diffuse bilateral densities, often associated with areas of hyperinflation). More recently, the definition has been modified to specify a need for supplemental oxygen for greater than 28 days or beyond 36 weeks’ postmenstrual age (PMA), accompanied by characteristic radiographic abnormalities.

This and subsequent modifications of the earlier definition were initiated by substantial changes in the BPD patient cohort, where application of different ventilation regimens and other significant changes in treatment procedures yielded not only an increased survival rate in the most immature infants but also a different appearance of lung injury, with the characteristic arrest of lung development ...

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