ESSENTIALS OF DIAGNOSIS
Acute onset of unilateral chest pain and dyspnea.
Minimal physical findings in mild cases; unilateral chest expansion, decreased tactile fremitus, hyperresonance, diminished breath sounds, mediastinal shift, cyanosis and hypotension in tension pneumothorax.
Presence of pleural air on chest radiograph.
Pneumothorax, or accumulation of air in the pleural space, is classified as spontaneous (primary or secondary), traumatic, or iatrogenic. Primary spontaneous pneumothorax occurs in the absence of an underlying lung disease, whereas secondary spontaneous pneumothorax is a complication of preexisting pulmonary disease. Traumatic pneumothorax results from penetrating or blunt trauma. Iatrogenic pneumothorax may follow procedures such as thoracentesis, pleural biopsy, subclavian or internal jugular vein catheter placement, percutaneous lung biopsy, bronchoscopy with transbronchial biopsy, and positive-pressure mechanical ventilation. Tension pneumothorax usually occurs in the setting of penetrating trauma, lung infection, cardiopulmonary resuscitation, or positive-pressure mechanical ventilation. In tension pneumothorax, the pressure of air in the pleural space exceeds ambient pressure throughout the respiratory cycle. A check-valve mechanism allows air to enter the pleural space on inspiration and prevents egress of air on expiration.
Primary pneumothorax affects mainly tall, thin boys and men between the ages of 10 and 30 years. It is thought to occur from rupture of subpleural apical blebs in response to high negative intrapleural pressures. Family history and cigarette smoking may also be important factors.
Secondary pneumothorax occurs as a complication of COPD, asthma, cystic fibrosis, tuberculosis, Pneumocystis pneumonia, menstruation (catamenial pneumothorax), and a wide variety of interstitial lung diseases, including sarcoidosis, lymphangioleiomyomatosis, Langerhans cell histiocytosis, and tuberous sclerosis. A history of Pneumocystis pneumonia is a risk factor for the development of pneumothorax. One-half of patients with pneumothorax in the setting of recurrent (but not primary) Pneumocystis pneumonia will develop pneumothorax on the contralateral side. The mortality rate of pneumothorax in Pneumocystis pneumonia is high.
Chest pain ranging from minimal to severe on the affected side and dyspnea occur in nearly all patients. Symptoms usually begin during rest and usually resolve within 24 hours even if the pneumothorax persists. Alternatively, pneumothorax may present with life-threatening respiratory failure if underlying lung disease is present.
If pneumothorax is small (less than 15% of a hemithorax), physical findings, other than mild tachycardia, are normal. If pneumothorax is large, diminished breath sounds, decreased tactile fremitus, and decreased movement of the chest are often noted. Tension pneumothorax should be suspected in the presence of marked tachycardia, hypotension, and mediastinal or tracheal shift.
Arterial blood gas analysis is often unnecessary but reveals hypoxemia and acute respiratory alkalosis in most patients. Left-sided primary pneumothorax may produce QRS axis and precordial T-wave changes on the ECG that may be misinterpreted as acute myocardial infarction.