Pulmonary air leak in the newborn

INTRODUCTION — Pulmonary air leak occurs more frequently in the newborn period than at any other time of life. It occurs when air escapes from the lung into extra-alveolar spaces where it is not normally present. The resulting disorders depend upon the location of the air. The most common conditions are pneumothorax, pneumomediastinum, pulmonary interstitial emphysema, and pneumopericardium. Rarer forms are pneumoperitoneum and subcutaneous emphysema.

PATHOPHYSIOLOGY — Air leak begins with the rupture of an overdistended alveolus [1]. Overdistention may be due to generalized air trapping or uneven distribution of gas. The air dissects along the perivascular connective tissue sheath toward the hilum, resulting in a pneumomediastinum, or into the pleural space, producing a pneumothorax [2]. Less commonly, air may dissect into the pericardial space, subcutaneous tissue, or peritoneal space, causing pneumopericardium, subcutaneous emphysema, and pneumoperitoneum, respectively.

The perivascular connective tissue is more abundant and less dissectible in preterm than in older infants. This predisposes to air trapping in the perivascular space, resulting in pulmonary interstitial emphysema [2].

INCIDENCE — Data on the incidence of air leak primarily reflect the incidence of pneumothorax because that disorder is most common. The incidence depends upon factors including birth weight (BW), the presence of lung disease, and the method of detection. In a report from 1930 in which chest radiographs were performed on 702 consecutive newborns, the incidence of spontaneous pneumothorax was 1 to 2 percent of live births, mostly in infants with otherwise normal lungs [3].

The incidence is higher in preterm infants, who often have pulmonary disease. In a report from the Vermont Oxford database, pneumothorax was reported in 6.3 percent of 26,007 infants with BW 500 to 1500 grams in 1999 [4]. Since that published report, the incidence of pneumothorax has decreased for infants with BW 500 to 1500 grams registered in the Vermont Oxford Network database to 4.5 percent in 2021 [5].

The incidence of spontaneous pneumomediastinum detected by screening symptomatic infants has been reported as 25 of 10,000 live births [6]. However, because pneumomediastinum is usually asymptomatic and may not be detected, the actual incidence is uncertain.

RISK FACTORS — Most cases of air leak occur in newborns with underlying lung disease, especially if mechanical ventilation is required. Preterm infants are at increased risk because they frequently have respiratory distress syndrome, although treatment with surfactant replacement reduces the incidence [7-9].

Air leak also complicates pulmonary disorders that affect term infants. Pneumothorax is a common complication of meconium aspiration syndrome, occurring in 10 to 30 percent of affected infants [10,11]. (See "Meconium aspiration syndrome: Pathophysiology, clinical manifestations, and diagnosis".)

Other conditions that predispose to pneumothorax include pulmonary hypoplasia (in which pneumothorax is often bilateral), pneumonia, and transient tachypnea of the newborn [12,13]. (See "Transient tachypnea of the newborn".)

Mechanical ventilation increases the risk of air leak. Contributing factors include high inspiratory pressure, large tidal volume, and long inspiratory duration. However, in a case-control study of ventilated newborns, inadvertent overventilation (indicated by low carbon dioxide tension) was not associated with pneumothorax [14].

PNEUMOTHORAX — Pneumothorax consists of air in the space between the parietal and visceral pleura.

Clinical features — Infants with a small pneumothorax may be asymptomatic. However, signs of respiratory distress such as tachypnea, grunting, pallor, and cyanosis usually accompany the disorder. An early sign of pneumothorax may be a sudden decrease of voltage of the QRS complex on the oscilloscopic cardiac tracing [15].

Findings on physical examination of the chest include:

●Chest asymmetry with enlargement of the affected side

●Decreased breath sounds on the affected side

●Shift of the point of maximal cardiac impulse away from the affected side

A large tension pneumothorax increases intrathoracic pressure, which may cause increased central venous pressure and decreased venous return. This, in turn, may result in decreased cardiac output, leading to hypotension, bradycardia, and hypoxemia.

Pneumothorax is often preceded by pulmonary interstitial emphysema or, less often, pneumomediastinum (image 1). Pneumothorax in respiratory distress syndrome has been associated with increased risk of intraventricular hemorrhage [16], chronic lung disease, and death [17,18]. Pneumothoraces may also be seen following open chest surgeries; however, prophylactic chest tube drainage of such air leaks has not been found to decrease postoperative complications [19].

Diagnosis — Pneumothorax should be suspected in any newborn with sudden onset of respiratory distress. The level of suspicion should be high in a mechanically ventilated infant with an unexplained deterioration in oxygenation, ventilation, or cardiovascular status.

Transillumination — Transillumination of the chest with a high-intensity fiberoptic probe in a darkened room may help make the diagnosis of pneumothorax. When the fiberoptic probe is placed against the chest wall, a pneumothorax lights up the affected hemithorax [20]. In a life-threatening situation, the air can be immediately evacuated. If the infant is stable or findings are equivocal, the diagnosis should be confirmed by chest radiograph before an intervention is made.

Chest radiograph — A large pneumothorax is usually easily seen on an anteroposterior chest radiograph. Characteristic findings are air in the pleural space outlining the visceral pleura (image 2), atelectasis with flattening of the diaphragm on the affected side, and shift of the mediastinum away from the pneumothorax. The affected side may appear hyperlucent because air accumulates anteriorly when the infant lies in the supine position.

Smaller pneumothoraces may be more difficult to appreciate. Detection may be improved by a radiograph taken with the infant in a lateral decubitus position, with the affected side up.

Ultrasonography — Ultrasound is another imaging modality that has been used to detect pneumothoraces [21,22]. While operator-dependent, ultrasound has been found to highly sensitive and specific [23]. As point-of-care ultrasound gains traction in NICUs, lung ultrasound may become preferred over chest radiography for rapid diagnosis of pneumothorax.

Management — Infants without a continuous air leak or respiratory distress and who have no underlying lung disease or have no need for assisted ventilation may be observed closely without specific treatment. The pneumothorax will typically resolve in one to two days. Infants with respiratory distress should be monitored closely. Oxygen supplementation should be provided as needed to maintain adequate saturation. (See "Respiratory support, oxygen delivery, and oxygen monitoring in the newborn".)

Infants with respiratory distress should be monitored closely. Oxygen supplementation should be provided as needed to maintain adequate saturation. The rate of resolution of spontaneous pneumothoraces is not improved with oxygen supplementation. This was illustrated in a large retrospective study that showed a similar rate of resolution between patients who received room air and those who were supplemented with high oxygen concentrations (11 versus 12 hours) [24]. As a result, and because of concerns regarding the risks of hyperoxia, we do not routinely administer supplemental oxygen above the concentration needed to maintain adequate saturation. (See "Respiratory support, oxygen delivery, and oxygen monitoring in the newborn".)

In mechanically ventilated infants, ventilator settings should be adjusted to minimize mean airway pressure by reducing peak inspiratory pressure, positive end-expiratory pressure, and inspiratory duration. In some cases of infants who do not require high ventilatory settings, spontaneous resolution may occur without chest tube placement.

This was illustrated in a retrospective study of 136 ventilated infants who developed pneumothoraces [25]. Of the 35 (26 percent) who were initially managed without the insertion of a chest tube, 14 were treated with needle thoracentesis and 21 were closely observed (expectant management). Resolution of the pneumothorax without further interventions occurred in 27 (77 percent) infants. Subsequent placement of a chest tube occurred in eight patients, two from the expectant management and six from the needle thoracentesis groups. Infants managed without an initial chest tube were on lower ventilator settings and had better arterial blood gas parameters than those who required initial placement of a chest tube.

Thoracentesis — Thoracentesis is used emergently for the treatment of a symptomatic pneumothorax. It may be the only intervention needed in an infant who is not mechanically ventilated and may be a temporizing measure in an infant who requires ventilation [25-27]. Thoracentesis involves needle aspiration of air with a syringe attached to a 23 or 25 gauge scalp vein needle or an 18 to 20 gauge angiocatheter.

Chest tube placement — Tension pneumothorax and pneumothorax that develops in a mechanically ventilated infant usually need chest tube placement for definitive drainage. In most cases, the tube is placed in the anterior pleural space and connected to an underwater seal with continuous suction at a pressure of 10 to 15 cm H₂O. The position of the tube and resolution of the pneumothorax should be documented by chest radiographs. Resolution usually occurs in two to three days, although the air leak sometimes recurs.

Complications of chest tube insertion include bruising of the diaphragm and mediastinal structures, and perforation of the lung. Hemorrhage, cardiac tamponade, and phrenic nerve injury may occur. (See "Diaphragmatic paralysis in the newborn".)

PNEUMOMEDIASTINUM — Pneumomediastinum consists of air in the mediastinal space.

Clinical features — Most cases of pneumomediastinum are asymptomatic. Large collections of air may result in tachypnea and cyanosis. Pneumomediastinum is usually suspected on the routine newborn examination when the heart sounds are distant.

Diagnosis — The diagnosis is made on a chest radiograph. If the amount of air is large, the pneumomediastinum can usually be appreciated on an anteroposterior view as a halo of air around the heart, or on a lateral view as a retrosternal or superior mediastinal radiolucency [6]. It is most reliably seen on a left anterior oblique view, in which even minimal air in the mediastinum surrounds the thymus and lifts it from the cardiac shadow, resulting in the characteristic "spinnaker sail" sign.

Management — Pneumomediastinum usually resolves spontaneously, and requires no specific treatment. The patient should be observed closely for evidence of cardio-respiratory compromise and development of other air leaks, especially pneumothorax. Infants with tension pneumomediastinum should be treated urgently with ultrasound-guided percutaneous drainage of the tension pneumomediastinum [28].

PULMONARY INTERSTITIAL EMPHYSEMA — Pulmonary interstitial emphysema (PIE) consists of air trapped in the perivascular tissues of the lung. This results in decreased compliance and overdistention of the lung. The interstitial air also compresses airways, resulting in increased airway resistance.

Clinical features — PIE typically affects mechanically ventilated extremely low birth weight infants and may involve one or both lungs [29-32]. It usually presents within 96 hours of birth with gradually worsening hypoxemia and hypercarbia. Ventilator settings are often increased in response to the poor gas exchange, which may exacerbate air trapping and lead to further worsening of oxygenation and ventilation. Overdistention of the lung may cause vascular compression, resulting in decreased venous return and impaired cardiac output [33]. PIE may precede the development of pneumothorax or other air leak.

Diagnosis — The diagnosis of PIE is made by chest radiograph. Interstitial air can appear as either cyst-like or linear radiolucencies. The former are approximately 1 to 4 mm in size, and must be distinguished from the bubbly pattern that often follows surfactant administration. The linear radiolucencies are coarse, non-branching streaks that are seen in both the peripheral and medial lung fields (image 3 and image 4). These must be distinguished from air bronchograms (eg, in respiratory distress syndrome), which are smooth, regular, branching structures and can be seen toward the hilum [34].

Management — There is no definitive treatment for PIE. Management is supportive and directed at providing adequate gas exchange and minimizing the risk of further air leak. This is best accomplished by decreasing the mean airway pressure as much as possible, which is achieved by reducing the peak inspiratory pressure, positive end expiratory pressure, and inspiratory duration. The inspired oxygen concentration should be increased to compensate for the decreased mean airway pressure. We often use high frequency ventilation in infants with PIE to avoid large cyclic swings in tidal volume, although trials of this intervention are not available [35,36].

Supportive management of unilateral PIE includes positioning the infant with the affected side down, minimal chest physiotherapy and endotracheal suctioning, and if possible, decreasing ventilator pressure and inspiratory times [37]. Placing the infant in the lateral decubitus position with the affected side down promotes aeration of the unaffected lung and reduces aeration of the lung with PIE, resulting in resolution of the PIE [38-40]. In severe cases of unilateral PIE that do not respond to supportive management, collapse of the affected lung by selective bronchial intubation of the contralateral lung or occlusion of the bronchus of the affected lung by use of a Swan-Ganz catheter may promote decompression and healing of the affected lung [41,42]. Where selective bronchial intubation of the contralateral lung is attempted, a minimum period of 48 hours has been advocated [43].

PNEUMOPERICARDIUM — Pneumopericardium is a rare condition caused by air in the pericardial space. However, it can cause cardiac tamponade that is life-threatening [44].

Clinical features — Pneumopericardium typically occurs in a mechanically ventilated preterm infant with severe respiratory distress syndrome who also has pneumothorax and/or pulmonary interstitial emphysema. The disorder is rare in an infant who does not require mechanical ventilation [45].

The typical presentation is the abrupt onset of hemodynamic compromise due to cardiac tamponade. Acute collapse may be preceded by tachycardia and a narrowed pulse pressure. Findings on physical examination include bradycardia, hypotension, increased respiratory distress, and cyanosis. The heart sounds may be muffled or distant. Some infants have a pericardial knock or a characteristic millwheel-like murmur. The electrocardiogram may show low voltages with a small QRS complex.

Diagnosis — The diagnosis is confirmed by chest radiograph. In the anteroposterior view, air is seen surrounding the heart shadow within the pericardium. The gas shadow does not extend beyond the reflection of the aorta and pulmonary artery (image 5) [46]. It may be difficult to differentiate pneumopericardium from pneumomediastinum. Air under the inferior surface of the heart is diagnostic of the former.

Transillumination with a high-intensity fiberoptic light source may be helpful while awaiting a chest radiograph. The presence of a pneumopericardium is suggested by illumination of the substernal region that may flicker with the heart rate. However, it is often difficult to distinguish pneumopericardium, pneumomediastinum, or a medial pneumothorax with this technique.

In life-threatening situations in which the diagnosis is strongly suspected, the diagnosis is made by a therapeutic pericardiocentesis. In these cases, a chest radiograph should be obtained after the procedure. (See 'Pericardial drainage' below.)

Management — Infants who are asymptomatic may not need intervention. They should be closely observed with frequent monitoring of vital signs, including pulse pressure, and chest radiographs. As with any air leak in an infant receiving mechanical ventilation, ventilator pressures should be minimized [46].

Pericardial drainage — Symptomatic infants require pericardial drainage. Immediate aspiration of the pneumopericardium by pericardiocentesis should be performed in an infant with tamponade. This procedure is both diagnostic and therapeutic. Vital signs should improve as the air is aspirated. However, the air often reaccumulates and tamponade may recur. Thus, continuous decompression with a pericardial tube may be necessary [47].

OTHER AIR LEAKS — Pneumoperitoneum and subcutaneous emphysema are uncommon types of air leak. Pneumoperitoneum may occur when extrapulmonary air decompresses into the peritoneal cavity [48]. The diagnosis is made on an abdominal radiograph and usually has little clinical significance. However, it must be differentiated from intraperitoneal air due to a perforated viscus.

Subcutaneous emphysema typically occurs in the face, neck, or supraclavicular region. It typically presents as crepitus detected by palpation. It usually has no clinical significance, although large air collections in the neck may cause tracheal compromise.

SUMMARY

●Definition and risk factors – Pulmonary air leak occurs when air escapes from the lung into extra-alveolar spaces. It occurs most commonly in the newborn period, especially in preterm infants with respiratory distress syndrome who require mechanical ventilation. (See 'Incidence' above and 'Risk factors' above.)

●Pneumothorax is the most common cause – The most common pulmonary air leak condition is pneumothorax (air in the space between the parietal and visceral pleura). Patients may present with signs of respiratory distress or be asymptomatic in cases of small pneumothorax. The diagnosis is made by chest radiography. Management is dependent upon the size of the pneumothorax and whether or not the infant has respiratory disease requiring significant mechanical ventilation. Management options include evacuation of air by either thoracentesis or chest tube placement, or close observation with the expectation of spontaneous resolution of the air leak. (See 'Pneumothorax' above.)

●Other causes – Other pulmonary air leak conditions include pneumomediastinum, pulmonary interstitial emphysema, and pneumopericardium, and, rarely, pneumoperitoneum and subcutaneous emphysema. (See 'Pneumomediastinum' above and 'Pulmonary interstitial emphysema' above and 'Pneumopericardium' above and 'Other air leaks' above.)