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Pulmonary interstitial emphysema is leakage of air from alveoli into the pulmonary interstitium, lymphatics, or subpleural space. It usually occurs in infants with poor lung compliance, such as those with respiratory distress syndrome who are being treated with mechanical ventilation, but it may occur spontaneously. One or both lungs may be involved, and pathology may be focal or generalized within each lung. If dissection of air is widespread, respiratory status may acutely worsen because lung compliance suddenly is reduced.

Chest x-ray shows a variable number of cystic or linear lucencies in the lung fields. Some lucencies are elongated; others appear as enlarged subpleural cysts ranging from a few millimeters to several centimeters in diameter.

This air-leak syndrome may resolve dramatically over 1 or 2 days or persist on x-ray for weeks. Some infants with severe respiratory disease and pulmonary interstitial emphysema develop bronchopulmonary dysplasia (BPD), and the cystic changes of long-standing pulmonary interstitial emphysema then merge into the x-ray picture of BPD.

Treatment of pulmonary interstitial emphysema is mainly supportive. For mechanically ventilated infants, lowering tidal volume and airway pressure by switching to a high-frequency oscillatory ventilator or high-frequency jet ventilator may help. If one lung is significantly more involved than the other, the infant may be laid down on the side of the lung with the more severe pulmonary interstitial emphysema; this will help to compress the lung with pulmonary interstitial emphysema, thereby decreasing air leakage and perhaps improving ventilation of the normal (elevated) lung. If one lung is very severely affected and the other is mildly affected or uninvolved, differential bronchial intubation and ventilation of the less-involved lung also may be attempted. However, it can be technically challenging to selectively intubate the left main bronchus; total atelectasis of the nonintubated lung soon results. Because only one lung is now being ventilated, ventilator settings and fraction of inspired oxygen (FIO2) may need to be altered. After 24 to 48 hours, the endotracheal tube is pulled back into the trachea, at which time the air leak may have stopped.

Pneumomediastinum is dissection of air into connective tissue of the mediastinum (see also Viral Pleuritis); the air may further dissect into the subcutaneous tissues of the neck and scalp.

Pneumomediastinum usually causes no symptoms or signs, but subcutaneous air causes crepitus.

Diagnosis of pneumomediastinum is by x-ray. In an anteroposterior view, air may form a lucency around the heart and the air lifts the lobes of the thymus away from the cardiac silhouette (spinnaker sail sign—so-called because it has the appearance of a boat sail).

No treatment of pneumomediastinum is usually needed, and the condition resolves spontaneously.

Pneumopericardium is dissection of air into the pericardial sac. It affects mechanically ventilated infants almost exclusively.

Most cases are asymptomatic, but if sufficient air accumulates, it can cause cardiac tamponade.

Diagnosis of pneumopericardium is suspected if infants have acute circulatory collapse and is confirmed by lucency around the heart on x-ray or by return of air on pericardiocentesis using an angiocatheter and syringe.

Treatment of pneumopericardium is pericardiocentesis followed by surgical insertion of a pericardial tube.

Pneumoperitoneum is dissection of air into the peritoneum. It is generally not clinically significant but must be distinguished from pneumoperitoneum due to a ruptured abdominal viscus, which is a surgical emergency.

Diagnosis of pneumoperitoneum is made by abdominal x-ray and physical examination. Clinical symptoms that include abdominal rigidity, absent bowel sounds, and signs of sepsis suggest abdominal viscus injury.

Pneumothorax is dissection of air into the pleural space; sufficient accumulation of air causes tension pneumothorax.

Although sometimes asymptomatic, pneumothorax typically causes worsening of tachypnea, grunting, and cyanosis. Breath sounds decrease, and the chest enlarges on the affected side. Tension pneumothorax causes cardiovascular collapse.

Diagnosis of pneumothorax is suspected by deterioration of respiratory status, by transillumination of the chest with a fiberoptic probe, or both. Diagnosis is confirmed by chest x-ray or, in the case of tension pneumothorax, return of air during thoracentesis.

About 15% of term and late preterm neonates with spontaneous pneumothorax develop persistent pulmonary hypertension. This complication illustrates the importance of close monitoring of these patients (1).

Most small pneumothoraces resolve spontaneously, but larger and tension pneumothoraces require evacuation of the air in the pleural cavity. In tension pneumothorax, a small (23- or 25-gauge) needle or an angiocatheter (18- or 20-gauge) and syringe can be used to temporarily evacuate free air from the pleural space. Definitive treatment is insertion of an 8 or 10 French chest tube attached to low intermittent suction. Follow-up auscultation, transillumination, and x-ray confirm that the tube is functioning properly.