Pneumothorax

A pneumothorax is collection of air in the pleural space between the lung and the chest wall. Symptoms typically include sudden onset of sharp, one-sided chest pain and shortness of breath. In a minority of cases, a one-way valve is formed by an area of damaged tissue, in which case the air pressure in the space between chest wall and lungs can be higher; this has been historically referred to as a tension pneumothorax, although its existence among spontaneous episodes is a matter of debate. This can cause a steadily worsening oxygen shortage and low blood pressure. This could lead to a type of shock called obstructive shock, which could be fatal unless reversed. Very rarely, both lungs may be affected by a pneumothorax. It is often called a "collapsed lung", although that term may also refer to atelectasis.
A primary spontaneous pneumothorax is one that occurs without an apparent cause and in the absence of significant lung disease. Its occurrence is fundamentally a nuisance. A secondary spontaneous pneumothorax occurs in the presence of existing lung disease. Smoking increases the risk of primary spontaneous pneumothorax, while the main underlying causes for secondary pneumothorax are COPD, asthma, and tuberculosis. A traumatic pneumothorax can develop from physical trauma to the chest or from a complication of a healthcare intervention.
Diagnosis of a pneumothorax by physical examination alone can be difficult. A chest X-ray, computed tomography scan, or ultrasound is usually used to confirm its presence. Other conditions that can result in similar symptoms include a hemothorax, pulmonary embolism, and heart attack. A large bulla may look similar on a chest X-ray.
A small spontaneous pneumothorax will typically resolve without treatment and requires only monitoring. This approach may be most appropriate in people who have no underlying lung disease. In a larger pneumothorax, or if there is shortness of breath, the air may be removed with a syringe or a chest tube connected to a one-way valve system. Occasionally, surgery may be required if tube drainage is unsuccessful, or as a preventive measure, if there have been repeated episodes. The surgical treatments usually involve pleurodesis or pleurectomy. Conservative management of primary spontaneous pneumothorax is noninferior to interventional management, with a lower risk of serious adverse events. About 17–23 cases of pneumothorax occur per 100,000 people per year. They are more common in men than women.

Signs and symptoms

A primary spontaneous pneumothorax tends to occur in a young adult without underlying lung problems, and usually causes limited symptoms. Chest pain and sometimes mild breathlessness are the usual predominant presenting features. In newborns tachypnea, cyanosis and grunting are the most common presenting symptoms. People who are affected by a PSP are often unaware of the potential danger and may wait several days before seeking medical attention. PSPs more commonly occur during changes in atmospheric pressure, explaining to some extent why episodes of pneumothorax may happen in clusters. It is rare for a PSP to cause a tension pneumothorax.
Secondary spontaneous pneumothoraces, by definition, occur in individuals with significant underlying lung disease. Symptoms in SSPs tend to be more severe than in PSPs, as the unaffected lungs are generally unable to replace the loss of function in the affected lungs. Hypoxemia is usually present and may be observed as cyanosis. Hypercapnia is sometimes encountered; this may cause confusion and – if very severe – may result in comas. The sudden onset of breathlessness in someone with chronic obstructive pulmonary disease, cystic fibrosis, or other serious lung diseases should therefore prompt investigations to identify the possibility of a pneumothorax.
Traumatic pneumothorax most commonly occurs when the chest wall is pierced, such as when a stab wound or gunshot wound allows air to enter the pleural space, or because some other mechanical injury to the lung compromises the integrity of the involved structures. Traumatic pneumothoraces have been found to occur in up to half of all cases of chest trauma, with only rib fractures being more common in this group. The pneumothorax can be occult in half of these cases, but may enlarge – particularly if mechanical ventilation is required. They are also encountered in people already receiving mechanical ventilation for some other reason.
Upon physical examination, breath sounds may be diminished on the affected side, partly because air in the pleural space dampens the transmission of sound. Measures of the conduction of vocal vibrations to the surface of the chest may be altered. Percussion of the chest may be perceived as hyperresonant, and vocal resonance and tactile fremitus can both be noticeably decreased. Importantly, the volume of the pneumothorax may not be well correlated with the intensity of the symptoms experienced by the victim, and physical signs may not be apparent if the pneumothorax is relatively small.

Tension pneumothorax

Tension pneumothorax is generally considered to be present when a pneumothorax leads to significant impairment of respiration and/or blood circulation. This causes a type of circulatory shock, called obstructive shock. Tension pneumothorax tends to occur in clinical situations such as ventilation, resuscitation, trauma, or in people with lung disease. It is a medical emergency and may require immediate treatment without further investigations.
The most common findings in people with tension pneumothorax are chest pain and respiratory distress, often with an increased heart rate and rapid breathing in the initial stages. Other findings may include quieter breath sounds on one side of the chest, low oxygen levels and blood pressure, and displacement of the trachea away from the affected side. Rarely, there may be cyanosis, altered level of consciousness, a hyperresonant percussion note on examination of the affected side with reduced expansion and decreased movement, pain in the epigastrium, displacement of the apex beat, and resonant sound when tapping the sternum.
Tension pneumothorax may also occur in someone who is receiving mechanical ventilation, in which case it may be difficult to spot as the person is typically receiving sedation; it is often noted because of a sudden deterioration in condition. Recent studies have shown that the development of tension features may not always be as rapid as previously thought. Deviation of the trachea to one side and the presence of raised jugular venous pressure are not reliable as clinical signs.

Cause

Primary spontaneous

Spontaneous pneumothoraces are divided into two types: primary, which occurs in the absence of known lung disease, and secondary, which occurs in someone with underlying lung disease. The cause of primary spontaneous pneumothorax is unknown, but established risk factors include being of the male sex, smoking, family history of pneumothorax, and a tall, thin build. Smoking either cannabis or tobacco increases the risk. The various suspected underlying mechanisms are discussed [|below].

Secondary spontaneous

Secondary spontaneous pneumothorax occurs in the setting of a variety of lung diseases. The most common is chronic obstructive pulmonary disease, which accounts for approximately 70% of cases. The following known lung diseases may significantly increase the risk for pneumothorax.

Type	Causes
Diseases of the airways	COPD, acute severe asthma, cystic fibrosis
Infections of the lung	Pneumocystis pneumonia, tuberculosis, necrotizing pneumonia
Interstitial lung disease	Sarcoidosis, idiopathic pulmonary fibrosis, histiocytosis X, lymphangioleiomyomatosis
Connective tissue diseases	Rheumatoid arthritis, ankylosing spondylitis, polymyositis and dermatomyositis, systemic sclerosis, Marfan's syndrome and Ehlers–Danlos syndrome
Cancer	Lung cancer, sarcomas involving the lung
Miscellaneous	Catamenial pneumothorax

In children, additional causes include measles, echinococcosis, inhalation of a foreign body, and certain congenital malformations.
11.5% of people with a spontaneous pneumothorax have a family member who has previously experienced a pneumothorax. Several hereditary conditions – Marfan syndrome, homocystinuria, Ehlers–Danlos syndromes, alpha 1-antitrypsin deficiency, and Birt–Hogg–Dubé syndrome – have all been linked to familial pneumothorax. Generally, these conditions cause other signs and symptoms as well, and pneumothorax is not usually the primary finding. Birt–Hogg–Dubé syndrome is caused by mutations in the FLCN gene, which encodes a protein named folliculin. FLCN mutations and lung lesions have also been identified in familial cases of pneumothorax where other features of Birt–Hogg–Dubé syndrome are absent. In addition to the genetic associations, the HLA haplotype A₂B₄₀ is also a genetic predisposition to PSP.

Traumatic

A traumatic pneumothorax may result from either blunt trauma or penetrating injury to the chest wall. The most common mechanism is the penetration of sharp bony points at a new rib fracture, which damages lung tissue. Traumatic pneumothorax may also be observed in those exposed to blasts, even when there is no apparent injury to the chest.
Traumatic pneumothoraces may be classified as "open" or "closed". In an open pneumothorax, there is a passage from the external environment into the pleural space through the chest wall. When air is drawn into the pleural space through this passageway, it is known as a "sucking chest wound". A closed pneumothorax is when the chest wall remains intact.
Pneumothorax was reported as an adverse event caused by misplaced nasogastric feeding tubes. Avanos Medical's feeding tube placement system, the CORTRAK* 2 EAS, was recalled in May 2022 by the FDA due to adverse events reported, including pneumothorax, leading to 60 injuries and 23 people dying as communicated by the FDA.
Medical procedures, such as inserting a central venous catheter into one of the chest veins or taking biopsy samples from lung tissue, may also lead to pneumothorax. The administration of positive pressure ventilation, either mechanical ventilation or non-invasive ventilation, can result in barotrauma leading to a pneumothorax.
Divers who breathe from an underwater apparatus are supplied with breathing gas at ambient pressure, which results in their lungs containing gas at higher than atmospheric pressure. Divers breathing compressed air may develop a pneumothorax as a result of barotrauma from ascending just while breath-holding with their lungs fully inflated. An additional problem in these cases is that those with other features of decompression sickness are typically treated in a diving chamber with hyperbaric therapy; this can lead to a small pneumothorax rapidly enlarging and causing features of tension.