Pneumothorax

The pleural space lies between the parietal and visceral pleura and is normally negatively pressured at −5 mm Hg with fluctuations of 6 to 8 mm Hg between inspiration and expiration. With loss of the normal negative pressure, the affected lung collapses. Primary spontaneous pneumothorax occurs when a subpleural bleb, most commonly in the lung apex, ruptures into the pleural space. In secondary spontaneous pneumothorax, rupture of the visceral pleura and alveolar barrier is most commonly due to the underlying pulmonary disease process.

Pneumothorax

Classically, the symptoms of primary spontaneous pneumothorax are a sudden onset of ipsilateral, pleuritic chest pain and associated dyspnea. The pain typically begins at rest and is worsened with deep inspiration. It may eventually become a dull persistent ache that does not vary with respiration. Profound dyspnea is rare in the absence of tension pneumothorax or underlying parenchymal disease. Sinus tachycardia is the most common physical finding, with other classic signs such as decreased breath sounds, hyperresonance to percussion, unilateral enlargement of the hemithorax, absence of tactile fremitus, and decreased excursion volumes occurring less frequently. Symptoms may resolve in 24 hours without resolution of the pneumothorax. Many patients (45%) may delay seeking medical care for 48 hours. The severity of symptoms does not necessarily correlate with the size of the pneumothorax.

The ability of auscultation to detect hemothorax, pneumothorax, or hemopneumothorax associated with penetrating trauma had a sensitivity of 58%, a specificity of 98%, and a positive predictive value of 98% in one study.¹ Auscultation can miss up to 600 mL of hemothorax, a pneumothorax occupying up to 28% of lung volume, and a combined hemopneumothorax of up to 800 mL and 28%.¹ Physical examination alone is not sensitive enough to exclude the diagnosis of pneumothorax.

Open Pneumothorax

Patients with an open pneumothorax have significant dyspnea and a history of a penetrating wound to the thorax. Physical examination will reveal a chest wound that produces an audible, sucking air movement sound on inspiration and may bubble on expiration. Findings of a pneumothorax will also be present.

Tension Pneumothorax

Patients with tension pneumothorax exhibit extreme dyspnea, hypotension, and cyanosis. Physical findings are hyperresonance, hyperinflation, absence of breath sounds on the affected side, and deviation of the trachea (at the sternal notch) away from the affected side. Tachycardia is often present and is defined as a pulse greater than 120 beats/min. Patients with tachycardia should undergo immediate tube thoracostomy (or needle thoracostomy if a chest tube is not immediately available) without waiting for a confirmatory radiograph.

Secondary Pneumothoraces

Patients with pneumothoraces secondary to underlying lung disease may experience extreme dyspnea as a result of deflation of one lung and limited capacity and function of the remaining lung. Classically, symptoms do not resolve without intervention. Because of the underlying lung disease (most commonly COPD), lung findings may be abnormal, with hyperinflation and decreased lung sounds being noted.

Radiography

The primary evaluation tool is the standard posteroanterior chest radiograph to look for loss of lung markings in the periphery and a pleural line that runs parallel to the chest wall but does not extend outside the chest cavity. A lateral radiograph contributes to the diagnosis in 14% of cases.² There is no evidence that an expiratory radiograph adds any value even with small apical pneumothoraces.³ The sensitivity for flat anteroposterior chest radiography, versus computed tomography (CT) as the “gold standard,” has been found to be 75.5% (95% confidence interval [CI], 61.7% to 86.2%), and the specificity is 100% (95% CI, 97.1% to 100%).⁴

Table 51.1 Differential Diagnosis of Pneumothorax