A. Risk factors. The primary risk factors for air leak are mechanical ventilation and lung disorders. Risk factors common in premature infants include respiratory distress syndrome (RDS), sepsis, and pneumonia. Surfactant therapy for RDS has markedly decreased the incidence of pneumothorax. Risk factors common in term infants are aspiration of meconium, blood, or amniotic fluid; pneumonia; and congenital malformations.

B. Pathogenesis. Air leak syndromes arise via a common mechanism. Transpulmonary pressures that exceed the tensile strength of the noncartilagenous terminal airways and alveolar saccules can damage the respiratory epithelium. Loss of epithelial integrity permits air to enter the interstitium, causing pulmonary interstitial emphysema (PIE). Persistent elevation in transpulmonary pressure facilitates the dissection of air toward the visceral pleura and/or the hilum via the peribronchial and perivascular spaces. In rare circumstances, air can enter the pulmonary veins and result in air embolism. Rupture of the pleural surface allows the adventitial air to decompress into the pleural space, causing pneumothorax. Following a path of least resistance, air can dissect from the hilum and into the mediastinum, resulting in pneumomediastinum, or into the pericardium, resulting in pneumopericardium. Air in the mediastinum can decompress into the pleural space, the fascial planes of the neck and skin (subcutaneous emphysema), or the retroperitoneum. In turn, retroperitoneal air can rupture into the peritoneum (pneumoperitoneum) or dissect into the scrotum or labial folds.

1. Elevations in transpulmonary pressure. The infant’s first breath may cause a negative inspiratory pressure up to 100 cm H₂O. Uneven
ventilation due to atelectasis, surfactant deficiency, pulmonary hemorrhage, or retained fetal lung fluid can increase transpulmonary pressure. In turn, this leads to alveolar overdistention and rupture. Similarly, aspiration of blood, amniotic fluid, or meconium can facilitate alveolar overdistention by a ball-valve mechanism.

2. In the presence of pulmonary disease, positive pressure ventilation increases the risk of air leak. The high airway pressure required to achieve adequate oxygenation and ventilation in infants with poor pulmonary compliance (e.g., pulmonary hypoplasia, RDS, inflammation, pulmonary edema) further increases this risk. Excessive transpulmonary pressures can occur when ventilator pressures are not decreased as pulmonary compliance improves. This situation sometimes occurs in infants with RDS after surfactant treatment when compliance increases rapidly. Mechanically ventilated preterm infants who make expiratory efforts against ventilator breaths are also at increased risk for pneumothorax.

3. Direct trauma to the airways can also cause air leak. Laryngoscopes, endotracheal tubes, suction catheters, and malpositioned feeding tubes can damage the lining of the airways and provide a portal for air entry.

A. Pneumothorax. Spontaneous pneumothorax occurs in 0.07% of otherwise healthy-appearing neonates. One in 10 of these infants is symptomatic. The high inspiratory pressures and uneven ventilation that occur in the initial stages of lung inflation may contribute to this phenomenon. Pneumothorax is more common in newborns treated with mechanical ventilation for underlying pulmonary disease.

Clinical signs of pneumothorax range from insidious changes in vital signs to the complete cardiovascular collapse that often accompanies a tension pneumothorax. As intrathoracic pressure rises, there is decreased lung volume, mediastinal shift, compression of the large intrathoracic veins, and increased pulmonary vascular resistance. The net effect is an increase in central venous pressure, a decrease in preload, and, ultimately, diminished cardiac output. A pneumothorax must be considered in mechanically ventilated infants who develop unexplained alterations in hemodynamics, pulmonary compliance, or oxygenation and ventilation.

i. Signs of respiratory distress include tachypnea, grunting, flaring, and retractions.

ii. Cyanosis

iii. Chest asymmetry with expansion of the affected side

iv. Shift in the point of maximum cardiac impulse

v. Diminished or distant breath sounds on the affected side

vi. Alterations in vital signs. With smaller collections of extrapulmonary air, compensatory increases may occur in heart rate and blood pressure. As the amount of air in the pleural space increases, central venous pressure rises, and severe hypotension, bradycardia, apnea, hypoxia, and hypercapnia may occur.

b. Arterial blood gases. Changes in arterial blood gas measurements are nonspecific but sometimes reflect a decreased PO₂ and increased PCO₂. The pH may be low as PCO₂ rises or with metabolic acidosis due to poor cardiac output with tension pneumothorax.

c. Chest radiograph. Anteroposterior (AP) views may show a hyperlucent hemithorax, a separation of the visceral from the parietal pleura, flattening of the diaphragm, and mediastinal shift. Smaller collections of intrapleural air can be detected beneath the anterior chest wall by obtaining a cross-table lateral view; however, an AP view is needed to identify the affected side. The lateral decubitus view, with the side of suspected pneumothorax up, may be helpful in detecting a small pneumothorax and may help differentiate skin folds, congenital lobar emphysema, congenital pulmonary airway (cystic adenomatoid) malformations, and surface blebs that occasionally give the appearance of intrapleural air.

d. Transillumination. A high-intensity fiberoptic light source may demonstrate a pneumothorax. This technique is less sensitive in infants with chest wall edema or severe PIE, in extremely small infants with thin chest walls, or in full-term infants with thick chest walls or dark skin.

e. Needle aspiration. In a rapidly deteriorating clinical situation, thoracentesis may confirm the diagnosis and be therapeutic (see section II.A.2.b).

2. Treatment. Note that prior to any procedure, a “time out” or “hold point” should be done with the nurse to confirm the correct patient, diagnosis, and laterality (side affected).

a. Conservative therapy. Close observation may be adequate for infants who are asymptomatic. The extrapulmonary air will usually resolve in 24 to 48 hours. Oxygen should only be administered if the baby develops hypoxemia. No evidence supports the use of 100% oxygen to hasten the resolution of pneumothorax. Furthermore, unnecessary oxygen exposure can lead to free radical injury.

b. Needle aspiration. Thoracentesis with a “butterfly” needle or intravenous (IV) catheter with an inner needle can be used to treat a symptomatic pneumothorax. Needle aspiration may be curative in infants not receiving mechanical ventilation and is frequently a temporizing measure in mechanically ventilated infants. In infants with severe hemodynamic compromise, thoracentesis may be a life-saving procedure.

i. Attach a 23G or 25G butterfly needle or 22G or 24G IV catheter to a 10- to 20-mL syringe fitted with a three-way stopcock.