The definition of bronchopulmonary dysplasia (BPD) has been modified over the years. The initial description by Northway et al was followed by a definition of BPD that required a history of positive pressure ventilation during the first 2 weeks of life, clinical signs of respiratory compromise, and requirement for supplemental oxygen beyond 28 days of age, in addition to characteristic radiologic abnormalities. The current definition of chronic lung disease (CLD) in the newborn distinguishes between mild, moderate, and severe disease and uses O2 dependency at 36 weeks’ postconceptual age, thereby “correcting” for the degree of immaturity (Table 86-1). The disease is characterized by alveolar arrest and impaired vascular development, which is more significant at lower gestational ages.
Table 86-1Degrees of Bronchopulmonary Dysplasiaa ||Download (.pdf) Table 86-1Degrees of Bronchopulmonary Dysplasiaa
|Gestational Age at Birth ||<32 Weeks ||≥32 Weeks |
| ||FiO2 > 0.21 at day 28 |
|Mild ||FiO2 0.21 at 36 weeks ||FiO2 0.21 at day 56 |
|Moderate ||FiO2 < 0.30 at 36 weeks ||FiO2 < 0.30 at day 56 |
|Severe ||FiO2 ≥ 0.30 or PPV/CPAP at 36 weeks ||FiO2 ≥ 0.30 or PPV/CPAP at day 56 |
Clinical signs of CLD include evidence of respiratory distress, such as tachypnea, nasal flaring, and use of accessory muscles with intercostal and substernal retractions, grunting, and cyanosis. The decrease in gas exchange surface area leads to impaired gas exchange (ie, hypoxemia with need for supplemental O2 and alveolar hypoventilation with resultant hypercapnia) as a result of ventilation and perfusion mismatch. The clinical picture can be complicated by increased pulmonary vascular resistance, typically characterized by impaired responsiveness to inhaled nitric oxide (iNO) and other vasodilators, sometimes progressing to pulmonary hypertension and right heart failure. Biventricular failure is unusual when sufficient oxygenation is maintained, and the development of severe pulmonary hypertension is avoided. Pulmonary function testing in these infants often demonstrates increased airway resistance, hyperreactive airways, and reduced compliance. Infants can present with episodic bronchoconstriction and cyanosis. Increased work of breathing contributes to impaired somatic growth and neurologic development observed in severe cases from an early stage.
The diagnosis is defined by the need for supplemental oxygen or ventilator support to maintain oxygen saturation above 85% at 36 weeks’ postconceptual age. Blood gas analysis shows an increase in bicarbonate and partial pressure of carbon dioxide (pCO2), indicating increased ventilation-perfusion mismatch. Continuous pulse oximetry is needed to monitor oxygen saturation and control oxygen supply. Chest radiographic findings include fibrosis/interstitial markings, cystic elements, and hyperinflation ...