Bronchopulmonary dysplasia: then and now.

Bronchopulmonary dysplasia was first described in 1967 in a series of 32 infants with severe respiratory distress syndrome who were treated with artificial ventilation and supplemental oxygen. 1 These infants had initially been given antibiotics, the usual measures for control of body temperature, and glucose and sodium bicarbonate intravenously to combat acidosis. They had not responded to this treatment, were cyanotic in 100% oxygen, looked moribund, and had had one or more prolonged apnoeic spells. The clinical and radiological progression ofrespiratory distress syndrome was significantly modified by treatment with prolonged positive pressure ventilation, and 80-100% concentrations of oxygen. What was remarkable was the appearance of a new syndrome of chronic lung disease that was called bronchopulmonary dysplasia. The usual course of respiratory distress syndrome before the use of prolonged positive pressure ventilation was that infants who survived the first 3 days of life recovered completely and by 7-10 days of life had normal lungs radiographically.2 Those who died did so within four days. Chronic lung disease had not been seen as a sequel to respiratory distress syndrome before the description of bronchopulmonary dysplasia. The clinical, radiological, and pathological progression of bronchopulmonary dysplasia was initially divided into four stages.' Stage I (days 1-3) consisted of the initial clinical and radiological picture of respiratory distress syndrome. During stage II (days 4-10) there was increasing opacification of the lungs and, if the infant died, there was thick exudation into the lumen of the airway with patchy bronchiolar and alveolar epithelial necrosis with early stages of repair. At the end of stage II, weaning of the infants from the high concentrations of oxygen (80-100%) could usually be started. Stage III (days 10-20) was a period of transition to chronic lung disease with the chest radiograph showing a reticular network of small rounded areas of radiolucency that represented areas of emphysematous alveoli adjacent to atelectatic alveoli, and pulmonary fibrosis. This stage could be complicated by patent ductus arteriosus and congestive heart failure. In stage IV (after 30 days of age) there was persistent chronic lung disease with hyperexpansion and cystic looking lungs. The electrocardiogram at this stage usually showed right ventricular hypertrophy and cardiomegaly with cor pulmonale. Pathologically, there was emphysema with thickening of the lung interstitium, replacement of type I pulmonary epithelial cells with type II pneumocytes, squamous metaplasia and ulceration of bronchiolar epithelium, hypertrophy of bronchiolar smooth muscle, and early vascular lesions indicating pulmonary hypertension with periarteriolar thickening. Since the original description of bronchopulmonary dysplasia, it has been described all over the world in places where artificial ventilation and supplemental oxygen have been used to treat infants with severe respiratory distress syndrome. Bronchopulmonary dysplasia has become the most common form of chronic lung disease in infancy in the United States, with about 7000 new cases occurring each year (35 000 cases of respiratory distress syndrome/ year times a 0-20 incidence of bronchopulmonary dysplasia/per case of respiratory distress syndrome).3