The differential diagnosis of cyanosis and respiratory distress in the newborn is broad and includes respiratory distress syndrome, sepsis, meconium aspiration, diaphragmatic hernia, persistent pulmonary hypertension of the newborn (PPHN), cyanotic congenital heart disease, hypoglycemia, choanal atresia, and airway anomalies. The constellation of scaphoid abdomen (due to the absence of abdominal contents), barrel chest, bowel sounds in the chest, and the shift of heart sounds to the right is only consistent with CDH. To confirm the diagnosis, a chest radiograph should be performed to demonstrate gas-filled loops of bowel in the chest. The lung on the side of the hernia is compressed into the hilum, and the mediastinum is shifted to the opposite side of the chest. If in doubt, a radiopaque dye may be injected through a nasogastric tube to delineate the stomach and intestine in the chest.

The incidence of CDH is estimated to be between 1 in 2,500 and 1 in 3,000 births. Eighty-five percent of lesions are on the left side. Ninety percent are posterolateral (Bochdalek hernia). Anteromedial and paraesophageal hernias and eventrations make up the remainder (Fig. 37.1).

Infants with CDH have deficient bilateral major airway and vessel branching not explained by simple compression of the ipsilateral and contralateral lungs. The mechanisms for these abnormalities and the resultant lung and vascular hypoplasia are not known. The severity of pulmonary vascular hypoplasia correlates with mortality in CDH. Airway maldevelopment leads to reduced total number of alveoli at birth, with resultant low lung compliance and decreases in both ventilation and surface area for gas exchange. Oxygenation is thus impaired. Pulmonary vascular hypoplasia results in pulmonary hypertension, causing right-to-left shunting through the patent ductus arteriosus, with resultant hypoxemia.

Prenatally, the degree of pulmonary hypoplasia is estimated using ultrasound. Lung-to-head circumference and diameter of the proximal pulmonary artery indexed to the descending aorta are two measurements used to estimate risk of severe pulmonary hypoplasia. Intrathoracic position of the liver prenatally independently predicts poor outcome.

Postnatally, the severity of pulmonary hypoplasia is apparent in the clinical presentation of the infant, in that infants who are born with severe hypoplasia exhibit symptoms immediately after birth and require mechanical ventilation immediately. Inability to be resuscitated in the delivery room is a marker of lethal lung hypoplasia. Most centers will not attempt emergency ECMO in this situation.