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A pneumothorax (''pneumo-'' + ''thorax''; plural pneumothoraces) is an abnormal collection of air or gas in the pleural space that causes an uncoupling of the lung from the chest wall. Like pleural effusion (liquid buildup in that space), pneumothorax may interfere with normal breathing. It is often called collapsed lung, although that term may also refer to atelectasis. A primary pneumothorax is one that occurs without an apparent cause and in the absence of significant lung disease, while a secondary pneumothorax occurs in the presence of existing lung pathology. In a minority of cases, the amount of air in the chest increases markedly when a one-way valve is formed by an area of damaged tissue, leading to a tension pneumothorax. This condition is a medical emergency that can cause steadily worsening oxygen shortage and low blood pressure. Unless reversed by effective treatment, these sequelae can progress and cause death. Pneumothoraces can be caused by physical trauma to the chest (including blast injury), or as a complication of medical or surgical intervention. Symptoms typically include chest pain and shortness of breath. Diagnosis of a pneumothorax by physical examination alone can be difficult or inconclusive (particularly in smaller pneumothoraces), so a chest radiograph or computed tomography (CT) scan is usually used to confirm its presence. Small spontaneous pneumothoraces typically resolve without treatment and require only monitoring. This approach may be most appropriate in subjects who have no significant underlying lung disease. In larger pneumothoraces, or when there are marked symptoms, the air may be extracted with a syringe or a chest tube connected to a one-way valve system. Occasionally, surgical interventions may be required when tube drainage is unsuccessful, or as a preventive measure, if there have been repeated episodes. The surgical treatments usually involve pleurodesis (in which the layers of pleura are induced to stick together) or pleurectomy (the surgical removal of pleural membranes). ==Signs and symptoms== A primary spontaneous pneumothorax (PSP) 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. People who are affected by PSPs are often unaware of 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 PSPs to cause tension pneumothoraces.〔 Secondary spontaneous pneumothoraces (SSPs), 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 (decreased blood-oxygen levels) is usually present and may be observed as cyanosis (blue discoloration of the lips and skin). Hypercapnia (accumulation of carbon dioxide in the blood) 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 (COPD), 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 (not readily apparent) in half of these cases, but may enlarge - particularly if mechanical ventilation is required.〔 They are also encountered in patients already receiving mechanical ventilation for some other reason.〔 Upon physical examination, breath sounds (heard with a stethoscope) 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 (like a booming drum), and vocal resonance and tactile fremitus can both be noticeably decreased. Importantly, the volume of the pneumothorax can show limited correlation with the intensity of the symptoms experienced by the victim,〔 and physical signs may not be apparent if the pneumothorax is relatively small.〔〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pneumothorax」の詳細全文を読む スポンサード リンク
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