Pulmonary Air-Leak Syndromes
Pulmonary air-leak syndromes involve dissection of air out of the normal pulmonary airspaces.
Air-leak syndromes include
Pneumothorax and pneumomediastinum occur in 1 to 2% of normal neonates, probably because large negative intrathoracic forces created when the neonate starts breathing occasionally disrupt alveolar epithelium, which allows air to move from the alveoli into extra-alveolar soft tissues or spaces.
Air leak is more common and severe among neonates with lung disease, who are at risk because of poor lung compliance and the need for high airway pressures (eg, in respiratory distress) or because of air trapping (eg, meconium aspiration syndrome [see Meconium Aspiration Syndrome]), which leads to alveolar overdistention.
Many affected neonates are asymptomatic; diagnosis is suspected clinically or because of deterioration in O2 status and is confirmed by x-ray. Treatment varies by type of air leak but in ventilated infants always involves lowering inspiratory pressures to lowest tolerated settings. High-frequency ventilators may be helpful but are of unproven benefit.
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 (see Respiratory Distress Syndrome in Neonates) 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.
Pulmonary interstitial emphysema 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—see Bronchopulmonary Dysplasia (BPD)), and the cystic changes of long-standing pulmonary interstitial emphysema then merge into the x-ray picture of BPD.
Treatment 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; total atelectasis of the nonintubated lung soon results. Because only one lung is now being ventilated, ventilator settings and fraction of inspired O2 may need to be altered. After 24 to 48 h, 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 Pneumomediastinum); 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 is by x-ray; in an anteroposterior view, air may form a lucency around the heart, whereas on a lateral view, air lifts the lobes of the thymus away from the cardiac silhouette (spinnaker sail sign). No treatment 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 (see Pathophysiology). Diagnosis is suspected if infants experience 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 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 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 (see 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 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.
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 continuous suction. Follow-up auscultation, transillumination, and x-ray confirm that the tube is functioning properly.