Etiology of Pneumothorax
Primary spontaneous pneumothorax occurs in patients without underlying pulmonary disease, classically in tall, thin young men in their teens and 20s. It is thought to be due to spontaneous rupture of subpleural apical blebs or bullae that result from smoking or that are inherited. It generally occurs at rest, although some cases occur during activities involving reaching or stretching. Primary spontaneous pneumothorax also occurs during diving and high-altitude flying.
Secondary spontaneous pneumothorax occurs in patients with underlying pulmonary disease. It most often results from rupture of a bleb or bulla in patients with severe chronic obstructive pulmonary disease Chronic Obstructive Pulmonary Disease (COPD) Chronic obstructive pulmonary disease (COPD) is airflow limitation caused by an inflammatory response to inhaled toxins, often cigarette smoke. Alpha-1 antitrypsin deficiency and various occupational... read more (forced expiratory volume in one second [FEV1] < 1 L), HIV-related Pneumocystis jirovecii infection Pneumocystis jirovecii Pneumonia Pneumocystis jirovecii is a common cause of pneumonia in immunosuppressed patients, especially in those infected with human immunodeficiency virus (HIV) and in those receiving systemic... read more , cystic fibrosis Cystic Fibrosis Cystic fibrosis is an inherited disease of the exocrine glands affecting primarily the gastrointestinal and respiratory systems. It leads to chronic lung disease, exocrine pancreatic insufficiency... read more , or any underlying pulmonary parenchymal disease (see table Causes of Secondary Spontaneous Pneumothorax Causes of Secondary Spontaneous Pneumothorax ). Secondary spontaneous pneumothorax is more serious than primary spontaneous pneumothorax because it occurs in patients whose underlying lung disease decreases their pulmonary reserve.
Catamenial pneumothorax is a rare form of secondary spontaneous pneumothorax that occurs within 48 hours of the onset of menstruation in premenopausal women and sometimes in postmenopausal women taking estrogen. The cause is intrathoracic endometriosis, possibly due to migration of peritoneal endometrial tissue through diaphragmatic defects or embolization through pelvic veins.
Traumatic pneumothorax Pneumothorax (Traumatic) Traumatic pneumothorax is air in the pleural space resulting from trauma and causing partial or complete lung collapse. Symptoms include chest pain from the causative injury and sometimes dyspnea... read more is a common complication of penetrating or blunt chest injuries.
Iatrogenic pneumothorax is caused by medical interventions, including transthoracic needle aspiration, thoracentesis, central venous catheter placement, mechanical ventilation, and cardiopulmonary resuscitation.
Pathophysiology of Pneumothorax
Intrapleural pressure is normally negative (less than atmospheric pressure) because of inward lung and outward chest wall recoil. In pneumothorax, air enters the pleural space from outside the chest or from the lung itself via mediastinal tissue planes or direct pleural perforation. Intrapleural pressure increases, and lung volume decreases.
Tension pneumothorax Pneumothorax (Tension) Tension pneumothorax is accumulation of air in the pleural space under pressure, compressing the lungs and decreasing venous return to the heart. (See also Overview of Thoracic Trauma.) Tension... read more is a pneumothorax causing a progressive rise in intrapleural pressure to levels that become positive throughout the respiratory cycle and collapses the lung, shifts the mediastinum, and impairs venous return to the heart. Air continues to get into the pleural space but cannot exit. Without appropriate treatment, the impaired venous return can cause systemic hypotension and respiratory and cardiac arrest (pulseless electrical activity) within minutes. Tension pneumothorax most commonly occurs in patients receiving positive-pressure ventilation (with mechanical ventilation or particularly during resuscitation). Rarely, it is a complication of traumatic pneumothorax, when a chest wound acts as a one-way valve that traps increasing volumes of air in the pleural space during inspiration.
Symptoms and Signs of Pneumothorax
Small pneumothoraces are occasionally asymptomatic. Symptoms of pneumothorax include dyspnea and pleuritic chest pain. Dyspnea may be sudden or gradual in onset depending on the rate of development and size of the pneumothorax. Pain can simulate pericarditis Pericarditis Pericarditis is inflammation of the pericardium, often with fluid accumulation in the pericardial space. Pericarditis may be caused by many disorders (eg, infection, myocardial infarction, trauma... read more , pneumonia Overview of Pneumonia Pneumonia is acute inflammation of the lungs caused by infection. Initial diagnosis is usually based on chest x-ray and clinical findings. Causes, symptoms, treatment, preventive measures, and... read more , pleuritis Viral Pleuritis Viral pleuritis is a viral infection of the pleurae. Viral pleuritis is most commonly caused by infection with coxsackie B virus. Occasionally, echovirus causes a rare condition known as epidemic... read more , pulmonary embolism, musculoskeletal injury (when referred to the shoulder), or an intra-abdominal process (when referred to the abdomen). Pain can also simulate cardiac ischemia, although typically the pain of cardiac ischemia is not pleuritic.
Physical findings classically consist of absent tactile fremitus, hyperresonance to percussion, and decreased breath sounds on the affected side. If the pneumothorax is large, the affected side may be enlarged with the trachea visibly shifted to the opposite side. With tension pneumothorax, hypotension can occur.
Diagnosis of Pneumothorax
The diagnosis is suspected in stable patients with dyspnea or pleuritic chest pain and is confirmed with upright inspiratory chest x-ray. Radiolucent air and the absence of lung markings juxtaposed between a shrunken lobe or lung and the parietal pleura are diagnostic of pneumothorax. Tracheal deviation and mediastinal shift occur with large pneumothoraces.
The size of a pneumothorax is defined as the percentage of the hemithorax that is vacant. This percentage is estimated by taking 1 minus the ratio of the cubes of the width of the lung and hemithorax. For example, if the width of the hemithorax is 10 cm and the width of the lung is 5 cm, the ratio is 53/103= 0.125. Thus, the size of the pneumothorax is about 1 minus 0.125, or 87.5%. If adhesions are present between the lung and the chest wall, the lung does not collapse symmetrically, the pneumothorax may appear atypical or loculated, and the calculation is not accurate.
Small pneumothoraces (eg, < 10%) are sometimes overlooked on chest x-ray. In patients with possible pneumothorax, lung markings should be traced to the edge of the pleura on chest x-ray. Conditions that mimic pneumothorax radiographically include emphysematous bullae, skinfolds, folded bed sheets, and overlap of stomach or bowel markings on lung fields.
Pearls & Pitfalls
Treatment of Pneumothorax
Immediate needle decompression for tension pneumothoraces
Observation and follow-up x-ray for small, asymptomatic, primary spontaneous pneumothoraces
Catheter aspiration for large or symptomatic primary spontaneous pneumothoraces
Tube thoracostomy for secondary and traumatic pneumothoraces
Patients should receive supplemental oxygen until chest x-ray results are available because oxygen accelerates pleural reabsorption of air. Treatment then depends on the type, size, and effects of the pneumothorax. Primary spontaneous pneumothorax that is < 20% and that does not cause respiratory or cardiac symptoms can be safely observed without treatment if follow-up chest x-rays done at about 6 and 48 hours show no progression. Larger or symptomatic primary spontaneous pneumothoraces should be evacuated by catheter aspiration. Tube thoracostomy is an alternative.
Catheter aspiration is accomplished by insertion of a small-bore (about 7 to 9 French) IV or pigtail catheter into the chest in the 2nd intercostal space at the midclavicular line. The catheter is attached to a 3-way stopcock and syringe. Air is withdrawn from the pleural space through the stopcock into the syringe and expelled into the room. The process is repeated until the lung re-expands or until 4 L of air are removed. If the lung expands, the catheter can be removed or kept in place attached to a one-way Heimlich valve (thus permitting ambulation), and the patient need not be hospitalized. If the lung does not expand, a chest tube should be inserted, and the patient should be hospitalized. Primary spontaneous pneumothoraces can also be managed initially with a chest tube attached to a water seal without or with suction. Patients with primary spontaneous pneumothoraces should also undergo smoking cessation Smoking Cessation Most smokers want to quit and have tried doing so with limited success. Effective interventions include cessation counseling and drug treatment, such as varenicline, bupropion, or a nicotine... read more counseling.
Tube thoracostomy How To Do Tube and Catheter Thoracostomy Surgical tube thoracostomy is insertion of a surgical tube into the pleural space to drain air or fluid from the chest. Pneumothorax that is recurrent, persistent, traumatic, large, under tension... read more is generally used to treat secondary and traumatic pneumothoraces. Symptomatic patients with iatrogenic pneumothoraces are best managed initially with aspiration.
Tension pneumothorax is a medical emergency and should be diagnosed clinically; time should not be wasted confirming the diagnosis with a chest x-ray. It should be treated immediately by needle thoracostomy How To Do Needle Thoracostomy Needle thoracostomy, also called needle decompression, is insertion of a needle into the pleural space to decompress a tension pneumothorax. Needle thoracostomy is an emergency, potentially... read more , which involves inserting a 14- or 16-gauge needle with a catheter through the chest wall in the 2nd intercostal space at the midclavicular line. The sound of high-pressure air escaping confirms diagnosis. The catheter can be left open to air or attached to a Heimlich valve. Emergency decompression must be followed immediately by tube thoracostomy, after which the catheter is removed.
Complications of Pneumothorax
The 3 main problems encountered when treating pneumothorax are
Failure of the lung to expand
Re-expansion pulmonary edema
Air leaks are usually due to the primary defect—ie, continued leakage of air from the lung into the pleural space—but can be due to air leaking around the chest tube insertion site if the site is not properly sutured and sealed. Air leaks are more common in secondary than in primary spontaneous pneumothorax. Most resolve spontaneously in < 1 week.
Failure of the lung to re-expand is usually due to one of the following:
Persistent air leak
Malpositioned chest tube
Blood pleurodesis (a blood patch), endobronchial valves, thoracoscopy, or thoracotomy should be considered if an air leak or an incompletely expanded lung persists beyond 1 week.
Re-expansion pulmonary edema occurs when the lung is rapidly expanded, as occurs when a chest tube is connected to negative pressure after the lung has been collapsed for > 2 days. Treatment is supportive, with oxygen, diuretics, and cardiopulmonary support as needed.
Prevention of Pneumothorax
Recurrence approaches 50% in the 3 years after initial spontaneous pneumothorax. The best preventive procedure is video-assisted thoracic surgery Thoracoscopy and Video-Assisted Thoracoscopic Surgery Thoracoscopy is a procedure in which an endoscope is introduced to visualize the pleural space. Thoracoscopy can be used for visualization (pleuroscopy) or for surgical procedures. Surgical... read more (VATS) in which blebs are stapled and pleurodesis is done with pleural abrasion, parietal pleurectomy, or talc insufflation; in some medical centers, thoracotomy is still used. These procedures are recommended when catheter aspiration fails to resolve spontaneous pneumothorax, when pneumothorax recurs, or when patients have secondary spontaneous pneumothorax. Recurrence after these procedures is < 5%. If thoracoscopy cannot be done or is contraindicated, chemical pleurodesis Malignant pleural effusion Pleural effusions are accumulations of fluid within the pleural space. They have multiple causes and usually are classified as transudates or exudates. Detection is by physical examination and... read more through a chest tube may be done; this procedure, though much less invasive, reduces the recurrence rate to only about 25%.
Primary spontaneous pneumothorax occurs in patients without underlying pulmonary disease, classically in tall, thin young men in their teens and 20s.
Secondary spontaneous pneumothorax occurs in patients with underlying pulmonary disease; it most often results from rupture of a bleb or bulla in patients with severe chronic obstructive pulmonary disease.
Diagnosis is by upright chest x-ray, except for tension pneumothorax, which is diagnosed clinically as soon as suspected.
Primary spontaneous pneumothorax that is < 20% and that does not cause respiratory or cardiac symptoms can be safely observed without treatment if follow-up chest x-rays done at about 6 and 48 hours show no progression.
Larger or symptomatic primary spontaneous pneumothoraces should be evacuated by catheter aspiration or tube thoracostomy.
Secondary and traumatic pneumothoraces are generally treated with tube thoracostomy.
Video-assisted thoracic surgery (VATS) and other procedures can help prevent recurrences of spontaneous pneumothorax, which otherwise occur in 50% of patients within 3 years.