Pneumothorax refers to the presence of air or gas in the pleural cavity between the visceral and parietal pleura, which results in violation of the pleural space, and although pediatric pneumothorax is uncommon, it can be life threatening.
Primary spontaneous pneumothorax occurs in children without known lung disease, whereas secondary spontaneous pneumothorax occurs as a complication of chronic or acute lung disease. Traumatic pneumothorax is caused by blunt or penetrating trauma to the chest. Iatrogenic pneumothorax is a complication of certain diagnostic or therapeutic procedures such as central line placement or as a consequence of mechanical ventilation.
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The image below depicts a radiograph of a neonate with pneumothorax.
If the pneumothorax was an isolated event and treatment was initiated early, the prognosis is excellent. The rate of recurrence of a simple spontaneous pneumothorax can be as high as 30% ipsilateral and 10% contralateral. A high incidence of recurrence is noted after the first episode of a secondary pneumothorax and in patients who participate in activities such as deep sea diving. Patients with cystic fibrosis have an especially high rate of recurrence.
If other trauma was sustained at the same time or tension pneumothorax occurred with subsequent shock and hypoperfusion, the prognosis worsens.
If the patient was allowed to be hypoxic for a long period, brain injury is possible.
Spontaneous pneumothorax occurs via rupture of the visceral pleura, whereas traumatic pneumothorax may occur following injury to either pleural layer. In both types, a loss of intrapleural negative pressure causes lung collapse.
The main physiologic consequences of a pneumothorax are a decrease in vital capacity and a decrease in partial pressure of oxygen (PaO2). Most patients with a pneumothorax have a reduced PaO2 and an increased alveolar-arterial oxygen tension difference. The reduction in PaO2 appears to be caused by areas with low ventilation-perfusion ratios, anatomic shunts, and alveolar hypoventilation.
Pneumothorax can be classified as either simple or complicated. In a simple pneumothorax, air in the pleural space does not build up significant pressure but allows the lung to collapse by 10-30% without further expansion of the pneumothorax. A small pneumothorax may be asymptomatic and well tolerated.
A complicated pneumothorax is progressive and consists of continued air leakage into the pleural space that cannot exit during exhalation. This results in progressive lung collapse. The continued air leak results in positive pressure within the hemithorax and displacement of the mediastinum (ie, tension pneumothorax).
Tension pneumothorax is a life-threatening emergency. The positive pressure results in collapse of the involved lung and a shift of the mediastinal structures to the contralateral side (see the following image). This causes a decrease in cardiac output as a consequence of decreased venous return and leads to rapidly progressive shock and death if not treated.
Simple or complicated pneumothorax is very common in both blunt (38%) and penetrating (64%) pediatric chest injuries. Cases not associated with trauma are generally due to a pulmonary bleb rupture, with subsequent air leakage into the pleural space. Inhalation of some toxic substances, most notably crack cocaine, can also lead to this condition.
Spontaneous secondary pneumothoraces may occur in patients with underlying lung diseases such as asthma, cystic fibrosis,  or pneumonia. When trauma results in pneumothorax, it may be secondary to blunt trauma or penetrating trauma. Penetrating trauma results in an open or communicating pneumothorax.
The annual incidence of primary spontaneous pneumothorax in the general population is estimated to be 5-10 per 100,000 population. Although all age groups are affected, the peak incidence of pneumothorax occurs in persons aged 16-24 years.
The disorder is less common in children than in adults  ; the rate of pneumothorax is relatively higher in the newborn period, even in full-term newborns, but it declines during infancy.  Premature neonates on mechanical ventilation are at high risk,  and limited data in young children suggest a strong male predominance of primary spontaneous pneumothorax.
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