Bronchopulmonary Dysplasia

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Bronchopulmonary Dysplasia

Chapter Objectives

After reading this chapter, you will be able to:

• List the anatomic alterations of the lungs associated with bronchopulmonary dysplasia.

• Describe the causes of bronchopulmonary dysplasia.

• List the cardiopulmonary clinical manifestations associated with bronchopulmonary dysplasia.

• Describe the general management of bronchopulmonary dysplasia.

• Describe the clinical strategies and rationales of the SOAP presented in the case study.

• Define key terms and complete self-assessment questions at the end of the chapter and on Evolve.

Key Terms

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FIGURE 37-1 Alveolar changes during the four stages of bronchopulmonary dysplasia. A, Stage I, the formation of hyaline membrane. B, Stage II, the development areas of metaplasia and necrosis. C, Stage III, extensive metaplasia, hyperplasia, and interstitial fibrosis. D, Stage IV, progressive destruction of alveoli and airways.

Anatomic Alterations of the Lungs

Bronchopulmonary dysplasia (BPD), also referred to as chronic lung disease of prematurity, is the most common chronic lung disease of prematurity. Historically, BPD was first described by Northway and colleagues in 1967 as a severe chronic lung injury in premature infants who survived hyaline membrane disease (i.e., respiratory distress syndrome [RDS]) after being treated with high levels of mechanical ventilation and oxygen exposure for prolonged periods of time. At that time Northway described the following four pathologic stages of BPD:

Stage I BPD was said to occur during the first 2 to 3 days of life. This stage is often indistinguishable from RDS. During this period, alveolar hyaline membranes, patches of atelectasis, and lymphatic dilation were seen. In addition, early signs of bronchial mucosal necrosis appeared during this time (see Figure 37-1, A). The chest radiographic findings revealed ground glass-like granular patterns and small lung volumes (Figure 37-2, A).

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FIGURE 37-2 A, Stage I; occurs during the first 2 to 3 days of life. The chest radiographic findings show ground glass–like granular patterns and small lung volumes. B, Stage II; occurs 4 to 10 days after birth. The chest x-ray film shows patchy opaque areas with bronchograms (areas of atelectasis) next to areas of dark translucency (areas of hyperinflation). C, Stage III; occurs at 11 to 30 days of age. The chest radiograph shows circular or cystic areas surrounded by patches of irregular density. D, Stage IV; occurs after 30 days of life. The chest radiographs shows fibrosis and edema with areas of consolidation adjacent to areas of overinflation. (From Taeusch WH, Ballard RA, Gleason CA: Avery’s diseases of the newborn, ed 8, Philadelphia, 2005, Saunders.)

Stage II BPD was said to occur 4 to 10 days after birth. Atelectasis was more extensive during this period. In addition, metaplasia of the normal lung tissue cells caused bronchial necrosis, cellular debris, partial airway obstruction, air trapping, and alveolar hyperinflation. The pathologic findings during Stage II were commonly described as alternating areas of atelectasis and of emphysema (see Figure 37-1, B). These changes appeared on chest x-ray films as patchy opaque areas with bronchograms (areas of atelectasis) next to areas of dark translucency (areas of hyperinflation) (see Figure 37-2, B).

    It is interesting to note that at the time of this description in 1967, the therapeutic usefulness of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP), as we know it today, had not yet been described. During this time period, the ventilation of these infants was with zero CPAP or PEEP—factors that contributed to severe atelectasis.

Stage III BPD was said to occur at 11 to 30 days of age. Pathologic findings included extensive bronchial and bronchiolar metaplasia and hyperplasia (an increased number of cells), interstitial fibrosis, and excessive bronchial airway secretions. In addition, the alveolar hyperinflation continued to form circular groups of emphysematous bullae that were surrounded by patches of atelectasis (see Figure 37-1, C). On the chest radiograph, the lungs began to show circular or cystic areas surrounded by patches of irregular density (see Figure 37-2, C).

Stage IV BPD was said to occur after 30 days of life. During this stage, massive fibrosis of the lung and destruction of the bronchial airways, alveoli, and pulmonary capillaries occured. Areas of emphysematous, or cystlike, areas continued to increase in size and number. Thin strands of atelectasis and normal alveoli were interspersed around emphysematous areas. In addition, pulmonary hypertension often developed, lymphatic and bronchial mucous gland deformation occurred, and excessive bronchial secretions continued to be a problem (see Figure 37-1, D). The chest radiographs revealed fibrosis and edema with areas of consolidation adjacent to areas of overinflation (see Figure 37-2, D). Table 37-1 provides a summary of the original BPD stages, with pathologic and radiologic correlates.

TABLE 37-1

Bronchopulmonary Dysplasia Staging (Northway)

Stage Days after Birth Radiologic Findings Pathologic Findings
I 2-3 Ground-glass granular pattern; small lung volume

II 4-10 Patchy opaque areas with bronchograms (areas of atelectasis) adjacent to areas of dark translucency (areas of hyperinflation) III 11-20 Circular or cystlike areas of hyperlucency, surrounded by patches of irregular density caused by atelectasis IV >30 Increased size and numbers of cystlike areas of hyperlucency, surrounded by thinner stands of radiodensity

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Northway WH Jr, Rosan RC, Porter DY: Pulmonary disease following respiratory therapy of hyaline-membrane disease: bronchopulmonary dysplasia, N Engl J Med 276:357-368, 1967.

The major pathologic or structural changes of the lungs associated with earlier descriptions of BPD are as follows:

The “New” Bronchopulmonary Dysplasia—Anatomic Alterations of the Lungs

Much has been learned about BPD since it was first described in 1967. During the late 1960s, BPD occurred predominantly in larger preterm infants born at 30 to 34 weeks’ gestation, with a history of severe respiratory distress necessitating aggressive ventilatory support and high oxygen concentrations for prolonged periods of time. Today, BPD as it was originally described has virtually disappeared. The infants who more commonly develop BPD today are those of very low birth weights and born at less than 26 weeks’ gestation. These infants are now usually managed with several new and improved therapeutic techniques—including prenatal maternal steroids, the use of postnatal exogenous surfactant, gentle ventilation techniques, low oxygen concentrations, nasal CPAP, fluid restriction, vitamin A, diuretics, bronchodilator therapy, bronchial hygiene therapy, postnatal corticosteroids, and inhaled nitric oxide.

In the “new” BPD, the pathologic findings of the lungs are described as “more uniformly inflated with minimal airway injury or fibrosis.” The major anatomic pathology is a decrease in alveolar number, called alveolar hypoplasia. In the very preterm infant with the “new” BPD, the lung is just completing the canalicular stage of development at the time of birth. It is believed that the interruption of the canalicular stage significantly disrupts the progress of alveolar growth and likely contributes to the development of the “new” BPD.

In response to the awareness of the “new” BPD, the National Institutes of Health sponsored a workshop on BPD, providing a new definition of BPD.* The new definition outlines specific diagnostic criteria, including the need for oxygen, positive pressure ventilation, and/or CPAP. The definition also includes the postnatal age to better assess the severity of BPD. Table 37-2 provides an overview of the new diagnostic criteria for the “new” BPD.

TABLE 37-2

Diagnostic Criteria for the “New” Bronchopulmonary Dysplasia (BPD)

Gestational Age <32 Weeks ≥32 weeks
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% 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% oxygen at 36 weeks PMA or discharge, whichever comes first Need* for <30% oxygen at 56 days postnatal age or discharge, whichever comes first
Severe BPD Need* for ≥30% oxygen and/or PPV or NCPAP at 36 weeks PMA or discharge, whichever comes first Need*

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