Pulmonary air leakage syndromes

Lung air leak syndromes involve the spread of air outside of its normal location in the airspaces of the lungs.

Pulmonary air-leak syndromes include pulmonary interstitial emphysema, pneumomediastinum, pneumothorax, pneumopericardium, pneumoperitoneum, and subcutaneous emphysema. These syndromes occur in 1 to 2% of healthy neonates, possibly due to the development of a significant negative pressure within the chest cavity when the infant begins to breathe and the occasional destruction of the alveolar epithelium, allowing air to escape from the alveoli into extraalveolar soft tissues or spaces. Air leaks are most common and severe in infants with lung disease, who are at risk because of poor lung compliance and the need for high airway pressures (in respiratory failure) or because air trapping (in meconium aspiration syndrome) leads to alveolar overdistension. Many affected infants are asymptomatic; The diagnosis is suspected clinically or by worsening O2 status and is confirmed by chest X-ray. Treatment varies depending on the type of leak but in children on mechanical ventilation always involves reducing inspiratory pressure to the lowest tolerable level. High-frequency ventilators may be effective but have no proven benefit.

Interstitial pulmonary emphysema

Interstitial emphysema is a leakage of air from the alveoli into the interstitial tissue and lymphatics of the lungs or subpleural space. It usually occurs in mechanically ventilated children with low lung compliance, such as those with respiratory distress syndrome, but may also occur spontaneously. One or both lungs may be affected, and within each lung the lesion may be focal or diffuse. If the process is widespread, respiratory status may deteriorate acutely as lung compliance suddenly decreases.

Chest radiography shows a variable number of cystic or linear lucencies in the lungs. Some lucencies are elongated; others appear as subpleural cysts ranging from a few millimeters to several centimeters in diameter.

Pulmonary interstitial emphysema may resolve in 1 to 2 days or persist on chest radiographs for weeks. Some patients with severe lung disease and pulmonary interstitial emphysema develop bronchopulmonary dysplasia, and the cystic changes of long-standing pulmonary interstitial emphysema then become part of the chest radiographic picture of BPD.

Treatment is usually supportive. If one lung is significantly more involved than the other, the infant may be positioned on the side of the more affected lung; this will tend to compress the lung with interstitial emphysema, thereby reducing air leakage and possibly improving ventilation of the normal (upper) lung. If one lung is very severely affected and the other has little or no lung involvement, separate intubation and ventilation of the less affected lung may be attempted; total atelectasis of the unventilated lung will soon develop. Since only one lung is now ventilated, it may be necessary to alter the ventilator parameters and the fraction of inspired oxygen. After 24 to 48 hours, the endotracheal tube is returned to the trachea, at which time the air leak may cease.

Pneumomediastinum

Pneumomediastinum is the penetration of air into the connective tissue of the mediastinum; the air may then penetrate into the subcutaneous tissues of the neck and head. Pneumomediastinum is usually asymptomatic, although crepitation is noted in the presence of subcutaneous air. Diagnosis is by radiography; in the anteroposterior projection, the air may form a lucency around the heart, while in the lateral projection, the air lifts the thymus lobes away from the cardiac shadow (sail sign). Usually, no treatment is required; improvement is spontaneous.

Pneumopericardium

Pneumopericardium is the penetration of air into the pericardial cavity. It is almost always observed only in children on mechanical ventilation. In most cases, it is asymptomatic, but if enough air accumulates, it can lead to cardiac tamponade. The diagnosis is suspected if the patient develops acute collapse and is confirmed by the detection of a lucency around the heart on an X-ray or by obtaining air during pericardiocentesis using a needle to puncture the veins of the head. Treatment involves pericardial puncture followed by surgical insertion of a tube into the pericardial cavity.

Pneumoperitoneum

Pneumoperitoneum is the penetration of air into the abdominal cavity. It is usually of no clinical significance, but a differential diagnosis should be made with pneumoperitoneum due to rupture of a hollow organ in the abdominal cavity, which is an acute surgical pathology.

Pneumothorax

Pneumothorax is the entry of air into the pleural space; sufficient accumulation of air may result in tension pneumothorax. Typically, pneumothorax presents clinically with tachypnea, dyspnea, and cyanosis, although asymptomatic pneumothorax may also occur. Breathing is weakened, and the chest enlarges on the affected side. Tension pneumothorax leads to cardiovascular collapse.

The diagnosis is suspected by worsening respiratory status and/or by transillumination of the chest with a fiberoptic probe. The diagnosis is confirmed by chest radiography or, in the case of tension pneumothorax, by obtaining air during thoracentesis.

In most cases, pneumothorax resolves spontaneously with a small amount of air in the pleural cavity, but tension pneumothorax or a large volume of air in the pleural cavity must be evacuated. In tension pneumothorax, a head vein puncture needle or an angiocatheter and syringe are used temporarily to evacuate the air. Definitive treatment is the insertion of a French No. 8 or No. 10 chest tube connected to a continuously operating aspirator. Subsequent auscultation, transillumination, and radiography confirm that the tube is functioning properly.