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Flail chest is a life-threatening medical condition that occurs when a segment of the rib cage breaks under extreme stress and becomes detached from the rest of the chest wall. It occurs when multiple adjacent ribs are broken in multiple places, separating a segment, so a part of the chest wall moves independently. The number of ribs that must be broken varies by differing definitions: some sources say at least two adjacent ribs are broken in at least two places, some require three or more ribs in two or more places. The flail segment moves in the opposite direction as the rest of the chest wall: because of the ambient pressure in comparison to the pressure inside the lungs, it goes in while the rest of the chest is moving out, and vice versa. This so-called "paradoxical breathing"〔(【引用サイトリンク】url=http://www.oxfordreference.com/view/10.1093/oi/authority.20110803100305151 )〕 can increase the work and pain involved in breathing. Studies have found that up to half of people with flail chest die.〔Influence of flail chest on outcome among patients with severe thoracic cage trauma. Velmahos GC, Vassiliu P, Chan LS, Murray JA, Berne TV, Demetriades D Int Surg. 2002;87(4):240.〕 Flail chest is invariably accompanied by pulmonary contusion, a bruise of the lung tissue that can interfere with blood oxygenation. Often, it is the contusion, not the flail segment, that is the main cause of respiratory failure in patients with both injuries. ==Signs and symptoms== Two of the symptoms of flail chest are chest pain and dyspnea.〔Athanassiadi, Kalliopi, Michalis Gerzounis, Nikolaos Theakos. Management of 150 flail chest injuries: analysis of risk factors affecting outcome. European Journal of Cardio-thoracic surgery 26. (2004). Pg 373-376.〕 The characteristic paradoxical motion of the flail segment occurs due to pressure changes associated with respiration that the rib cage normally resists: * During normal inspiration, the diaphragm contracts and intercostal muscles pull the rib cage out. Pressure in the thorax decreases below atmospheric pressure, and air rushes in through the trachea. The flail segment will be pulled in with the decrease in pressure while the rest of the rib cage expands. * During normal expiration, the diaphragm and intercostal muscles relax increasing internal pressure, allowing the abdominal organs to push air upwards and out of the thorax. However, a flail segment will also be pushed out while the rest of the rib cage contracts. The constant motion of the ribs in the flail segment at the site of the fracture is extremely painful, and, untreated, the sharp broken edges of the ribs are likely to eventually puncture the pleural sac and lung, possibly causing a pneumothorax. The concern about "mediastinal flutter" (the shift of the mediastinum with paradoxical diaphragm movement) does not appear to be merited. Pulmonary contusions are commonly associated with flail chest and that can lead to respiratory failure. This is due to the paradoxical motions of the chest wall from the fragments interrupting normal breathing and chest movement. Typical paradoxical motion is associated with stiff lungs, which requires extra work for normal breathing, and increased lung resistance, which makes air flow difficult.〔Bemelman M, Poeze M, Blokhuis TJ, and Leenen LP. Historic overview of treatment techniques for rib facturs and flail chest. Eur J Trauma Emerg Surg. 36(5): 407-415, 2010.〕 The respiratory failure from the flail chest requires mechanical ventilation and a longer stay in an intensive care unit.〔Marasco SF, Davies AR, Cooper J, Varma D, Bennett V, Nevill R, Lee G, Bailey M, & Fitzgerald M. Prospective Randomized Controlled Trial of Operative Rib Fixation in Traumatic Flail Chest. Journal of the American College of Surgeons 216(5): 924-932, 2013.〕 It is the damage to the lungs from the flail segments that are life-threatening. 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「flail chest」の詳細全文を読む スポンサード リンク
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