Pneumothorax and pneumomediastinum are examples of air leak syndromes in which air accumulates in the spaces outside the lung airways and alveoli. Pneumothorax refers to the abnormal presence of air in the pleural space, whereas pneumomediastinum describes accumulation of air in the mediastinum. Air leak can be traumatic, iatrogenic, or spontaneous. Primary air leak occurs in children without clinically apparent lung disease, and secondary pneumomediastinum and pneumothorax refer to those with known underlying pulmonary disease (e.g. asthma, cystic fibrosis). Air leak secondary to barotrauma from positive-pressure ventilation or after surgery is commonly categorized as iatrogenic.

The prevalence and incidence of air leak syndromes is better known in adults than in children. The majority of patients present in the second and third decade of life. Therefore older pediatric patients are often included within adult studies. The most recent pediatric data suggests that the overall incidence of spontaneous pneumothorax in patients less than 18 years of age is 3.41 per 100,000, with fewer than 7% occurring in children younger than 10 years of age.¹ Secondary pneumothorax occurs at an annual incidence of 0.6% in cystic fibrosis patients, and pneumomediastinum in 0.3% of asthmatic patients in a children’s emergency department setting.^2,3

PATHOPHYSIOLOGY

Although patients with primary spontaneous pneumothorax (PSP) do not have underlying lung disease, computed tomography (CT) and surgical findings show that the majority have subpleural bullae, which may be ipsilateral or contralateral to the pneumothorax. The cause of such bullae is not fully understood, but they probably represent imbalances in protease and antiprotease enzymes leading to emphysema-like changes. Cigarette smoking increases the risk of the development of pneumothorax by nearly 10 times, although the magnitude of the risk from secondhand exposure in pediatric patients is not known.⁴ A specific gene mutation for pulmonary cysts has been identified in some familial cases.⁵

Increased intra-alveolar pressure, often from inflammation of small airways, results in tension on the alveolar wall and, ultimately, rupture leading to pneumothorax. Alternatively, air leak occurring within the interstitium can track through the hilum and collect in the mediastinum (causing pneumomediastinum), or rupture into the pleural space leading to pneumothorax.⁵

CLINICAL PRESENTATION

Patients with PSP typically present with an acute onset of pleuritic chest pain, usually described as sharp initially, becoming dull over time, and frequently resolving after 24 hours even without treatment. Onset frequently occurs while the patient is at rest. Many patients endorse dyspnea. Ipsilateral shoulder pain and dry cough are also common.

Physical examination findings vary depending on the size of the pneumothorax. Patients with small pneumothoraces (i.e. <15% of the hemithorax) may show only tachycardia or subjective dyspnea, or may have completely normal findings. In those with larger pleural air collections, examination findings include decreased chest wall movement and decreased or absent breath sounds on the affected side. Hyperresonance and decreased fremitus may also be appreciated. More severe cases demonstrate increased work of breathing with accessory muscle use. Heart sounds may be decreased, particularly with anterior pneumothoraces. Isolated tachycardia is common. However, when accompanied by hypotension, cyanosis, jugular venous distention, or tracheal deviation then tension pneumothorax with tamponade physiology needs to be considered and immediate intervention is required.

DIFFERENTIAL DIAGNOSIS

The differential diagnosis for chest pain with or without associated respiratory symptoms includes cardiovascular, gastrointestinal, pulmonary/pleural, and chest wall diseases. The differential for pleuritic chest pain can be narrowed to include pneumonia, idiopathic or viral pleurisy, pulmonary embolism, pericarditis, costochondritis, or other chest wall pathology. Decreased breath sounds on physical examination may be secondary to pneumonia, severe bronchospasm, pleural effusion, foreign body aspiration, or poor respiratory effort. Anxiety disorder is also on the differential for patients with chest pain, tachycardia, and tachypnea. Radiographically, congenital lobar emphysema, skin folds, and overpenetrated films may be mistaken for pneumothoraces.

DIAGNOSTIC EVALUATION

Definitive diagnosis is made by chest radiograph. On posteroanterior or portable chest film, a linear shadow of thin visceral pleura is seen, along with absence of lung markings beyond the pleural line (see Figure 163-1A). Expiratory films may facilitate the diagnosis of a small apical pneumothorax, but a small study of adult patients suggests increased yield is insignificant in most cases and therefore not routinely required.⁶ On supine views, air tracks anteriorly and therefore identifying pneumothorax may be challenging. When clinical suspicion is high but routine films are unrevealing, a lateral decubitus view can help reveal the pleural line. Chest radiographs allow determination of pneumothorax size and may also show the presence or absence of underlying lung disease. In adults, validated formulas can be used to determine the size of pneumothoraces; however, they have not been shown to be accurate in children.^7-9 Therefore pneumothorax sizing in pediatrics often relies on visual approximation.

The role of CT in pediatric patients with pneumothoraces is not well defined. These scans are often able to show underlying blebs and bullae much more accurately than with chest radiography; however, the significance of blebs and natural history of this disease is not fully established (see Figure 163-2). There is some evidence in adults that the presence of blebs greater than 2 cm, places a patient at increased risk for recurrence; however, no similar data exist in children. In addition, scans performed with chest tubes in place or shortly after their removal may show artifact and should be interpreted cautiously. Therefore for those including CT as part of the diagnostic evaluation, a 6- to 8-week delay may be prudent.⁹ Given the risk of ionizing radiation in children, and the imprecise benefit of CT in this disease process, further study is needed before more definitive recommendations regarding use can be made in children.

Laboratory tests offer very little in the diagnosis or management of PSP. In cases where clinical circumstances dictate the need for arterial blood gas analysis, an increased alveolar-arterial gradient proportional to the size of the pneumothorax is commonly seen. Hypercapnia is rare in patients without underlying lung disease. Conversely, many patients demonstrate respiratory alkalosis secondary to associated tachypnea.

MANAGEMENT

Patients presenting with signs and symptoms consistent with tension pneumothorax require immediate needle thoracostomy without delaying for radiographic confirmation. Such patients may include those with pulseless electrical activity without a clear underlying cause. Tube thoracostomy should follow needle decompression in these patients.

Patients with a clinical presentation consistent with pneumothorax without tension physiology should receive supplemental oxygen, and continuous cardiorespiratory monitoring, including oxygen saturation during the period of evaluation. Figure 163-3 provides an algorithm for various management strategies.

The two goals of management of pneumothoraces are to re-expand the affected lung and prevent recurrences. A wide variety of therapeutic options exist. In adults, clinical decision making is supported by consensus statements; however, no such guidelines exist in pediatrics.^10,11 Therefore management depends on individual practice patterns, available resources, and patient or family preferences.

Observation without intervention is a reasonable approach for first episodes of PSP in otherwise healthy patients with no or minimal symptoms and a small (<15%) pneumothorax by radiograph. High-flow oxygen should be given to patients with pneumothoraces even with normal oxygen saturations to lower the partial pressure of nitrogen, which may in turn accelerate the rate of absorption of air from the pleural cavity. A small study of adult patients demonstrated that resorption occurs at a rate of approximately 2% per day in patients breathing room air, but can be increased to nearly 10% per day with supplemental oxygen.¹² Inpatient observation to show clinical and radiographic improvement in children is recommended.

Patients with more severe symptoms or those with a large (>15%) pneumothorax require active re-expansion of the affected lung. Manual aspiration with a large-bore needle or intravenous catheter has been utilized in adults, but safety concerns prevent widespread use of this approach in children.¹³ Therefore for larger pneumothoraces, tube thoracostomy is the standard of care. Pigtail (6.5 to 10.5 French) catheters have been shown to be safe and as effective as large-bore surgical thoracostomy tubes (16 to 32 French) for pneumothoraces and are less painful.^14,15 Low-level wall suction is indicated for patients with underlying lung disease or those who fail to show improvement with water seal setup alone. Serial chest radiographs should show re-expansion of the affected lung without a persistent air leak.