Chapter 68: Pneumothorax

INTRODUCTION AND EPIDEMIOLOGY

Pneumothorax arises when free air enters the potential space between the visceral and parietal lung pleura. Primary pneumothoraces occur without clinically apparent lung disease, either spontaneously or from penetration of the intrapleural space by trauma. Secondary pneumothoraces happen in patients with underlying lung disease.

The incidence of primary spontaneous pneumothorax admissions is 14.1 per 100,000 population age 15 years and older with a higher rate for males (20.8) than females (7.6), reflecting an increase over earlier years.^1,2 Associated factors increasing the risk of occurrence include cigarette smoking, male gender, mitral valve prolapse, Marfan’s syndrome, and changes in ambient pressure. Familial patterns also suggest an inherited association.² Physical activity or exertion can precipitate pneumothorax but is not a common pneumothorax-triggering factor. Traumatic pneumothoraces are iatrogenic or noniatrogenic. Noniatrogenic pneumothoraces are discussed in the Chapter 261, “Pulmonary Trauma.”

Causes of secondary spontaneous pneumothorax are listed in Table 68-1. Chronic obstructive pulmonary disease is the most common cause.^2,3 Pneumothorax occurs in 5% of patients with acquired immunodeficiency syndrome, often from subpleural necrosis secondary to Pneumocystis infection, and carries a high mortality. Because of a continued air leak due to necrosis of lung tissue, simple aspiration fails as treatment in this group of patients.

Hemopneumothorax occurs in 2% to 7% of patients with secondary pneumothorax; if associated with a large amount of blood in the pleural cavity, this can be life threatening.^4-8 Treating the underlying disease may help decrease the risk of future pneumothorax.

PATHOPHYSIOLOGY

Under normal conditions, the parietal and visceral pleura are in contact, sliding on each other. The pleural space is under negative and dynamic pressure (–5 mm Hg with fluctuations of 6 to 8 mm Hg between inspiration and expiration). The tendency of the chest wall is to expand and for the lungs to collapse from elastic recoil. With the loss of the normal negative pressure in the pleural space that “adheres” the visceral pleura (lungs) to the parietal pleura (ribs), the affected lung collapses. A primary spontaneous pneumothorax occurs when a subpleural bleb ruptures, disrupting pleural integrity and usually involving the lung apex.^7-9 In secondary spontaneous pneumothoraces, disruption of the visceral pleura occurs secondary to underlying pulmonary disease processes.

Once there is a break in the visceral pleura, air travels down a pressure gradient into the intrapleural space, until ...