Hemothorax is the presence of blood in the pleural space. The source of blood may be the chest wall, lung parenchyma, heart, or great vessels. Although some authors state that a hematocrit value of at least 50% is necessary to differentiate a hemothorax from a bloody pleural effusion, most do not agree on any specific distinction.
Prompt identification and treatment of traumatic hemothorax is an essential part of the care of the injured patient. The upright chest radiograph is the ideal primary diagnostic study in the evaluation of hemothorax (see Workup). In cases of hemothorax unrelated to trauma, a careful investigation for the underlying source must be performed while treatment is provided.
Tube thoracostomy drainage is the primary mode of treatment. Video-assisted thoracoscopic surgery (VATS) may be used. Thoracotomy is the procedure of choice for surgical exploration of the chest when massive hemothorax or persistent bleeding is present. (See Treatment.)
Hemorrhage from or within the chest has been detailed in numerous medical writings dating back to ancient times. While lesser forms of trauma were commonly treated in the ancient physician's daily practice, major injuries, especially those to the chest, were difficult to treat and often lethal.
By the 18th century, some treatment for hemothorax was available; however, controversy raged about its form. A number of surgeons, including John Hunter in 1794, advocated the creation of an intercostal incision and drainage of the hemothorax. Those of the opposing viewpoint believed that closure of chest wounds without drainage and other conservative forms of management of bloody collections in the chest were proper treatment.
While Hunter's method was effective in evacuating the hemothorax, the creation of an iatrogenic pneumothorax as a result of the procedure was associated with significant morbidity. On the other hand, wound closure or conservative management posed the possible risks of subsequent empyema with sepsis or persistent trapped lung with permanent reduction of pulmonary function.
Observing the advantages and dangers of both forms of therapy, Guthrie, in the early 1800s, gave credence to both viewpoints. He proposed the importance of early evacuation of blood through an existing chest wound; at the same time, he asserted that if bleeding from the chest persisted, the wound should be closed in the hope that existing intrathoracic pressure would halt the bleeding. If the desired effect was accomplished, he advised that the wound be reopened several days later for the evacuation of retained clotted blood or serous fluid.
By the 1870s, early hemothorax evacuation by trocar and cannula or by intercostal incision was considered standard practice. Not long after this, underwater seal drainage was described by a number of different physicians. This basic technique has remained the most common form of treatment for hemothorax and other pleural fluid collections to this day. 
Normally, the pleural space, which is between the parietal and visceral pleurae, is only a potential space. Bleeding into the pleural space may result from either extrapleural or intrapleural injury.
Traumatic disruption of the chest wall tissues with violation of the pleural membrane can cause bleeding into the pleural cavity. The most likely sources of significant or persistent bleeding from chest wall injuries are the intercostal and internal mammary arteries. In nontraumatic cases, rare disease processes within the chest wall (eg, bony exostoses) can be responsible.
Blunt or penetrating injury involving virtually any intrathoracic structure can result in hemothorax. Massive hemothorax or exsanguinating hemorrhage may result from injury to major arterial or venous structures contained within the thorax or from the heart itself. These include the aorta and its brachiocephalic branches, the main or branch pulmonary arteries, the superior vena cava and the brachiocephalic veins, the inferior vena cava, the azygos vein, and the major pulmonary veins.
Injury to the heart can produce a hemothorax if a communication exists between the pericardium and the pleural space.
Injury to the pulmonary parenchyma may cause hemothorax, but it is usually self-limited because pulmonary vascular pressure is normally low. Pulmonary parenchymal injury is usually associated with pneumothorax and results in limited hemorrhage.
Hemothorax resulting from metastatic malignant disease is usually from tumor implants that seed the pleural surfaces of the thorax.
Diseases of the thoracic aorta and its major branches, such as dissection or aneurysm formation, account for a large percentage of specific vascular abnormalities that can cause hemothorax. Aneurysms of other intrathoracic arteries such as the internal mammary artery have been described and are possible causes of hemothorax if rupture occurs.
A variety of unusual congenital pulmonary abnormalities, including intralobar and extralobar sequestration,  hereditary telangiectasia, and congenital arteriovenous malformations, can cause hemothorax.
Hemothorax can result from a pathologic process within the abdomen if blood escaping from the lesion is able to traverse the diaphragm through one of the normal hiatal openings or a congenital or acquired opening.
Bleeding into the pleural space can occur with virtually any disruption of the tissues of the chest wall and pleura or the intrathoracic structures. The physiologic response to the development of a hemothorax is manifested in two major areas: hemodynamic and respiratory. The degree of hemodynamic response is determined by the amount and rapidity of blood loss.
Hemodynamic changes vary, depending on the amount of bleeding and the rapidity of blood loss. Blood loss of up to 750 mL in a 70-kg man should cause no significant hemodynamic change. Loss of 750-1500 mL in the same individual will cause the early symptoms of shock (ie, tachycardia, tachypnea, and a decrease in pulse pressure).
Significant signs of shock with signs of poor perfusion occur with loss of blood volume of 30% or more (1500-2000 mL). Because the pleural cavity of a 70-kg man can hold 4 L of blood or more, exsanguinating hemorrhage can occur without external evidence of blood loss.
The space-occupying effect of a large accumulation of blood within the pleural space may hamper normal respiratory movement. In trauma cases, abnormalities of ventilation and oxygenation may result, especially if associated with injuries to the chest wall.
A large enough collection of blood causes the patient to experience dyspnea and may produce the clinical finding of tachypnea. The volume of blood required to produce these symptoms in a given individual varies depending on a number of factors, including organs injured, severity of injury, and underlying pulmonary and cardiac reserve.
Dyspnea is a common symptom in cases in which hemothorax develops in an insidious manner, such as those secondary to metastatic disease. Blood loss in such cases is not so acute as to produce a visible hemodynamic response, and dyspnea is often the predominant complaint.
Physiologic resolution of hemothorax
Blood that enters the pleural cavity is exposed to the motion of the diaphragm, the lungs, and other intrathoracic structures. This results in some degree of defibrination of the blood so that incomplete clotting occurs. Within several hours of cessation of bleeding, lysis of existing clots by pleural enzymes begins.
Lysis of red blood cells results in a marked increase in the protein concentration of the pleural fluid and an increase in the osmotic pressure within the pleural cavity. This elevated intrapleural osmotic pressure produces an osmotic gradient between the pleural space and the surrounding tissues that favors transudation of fluid into the pleural space. In this way, a small and asymptomatic hemothorax can progress into a large and symptomatic bloody pleural effusion.
Late physiologic sequelae of unresolved hemothorax
Two pathologic states are associated with the later stages of hemothorax: empyema and fibrothorax. Empyema results from bacterial contamination of the retained hemothorax. If undetected or improperly treated, this can lead to bacteremia and septic shock.
Fibrothorax results when fibrin deposition develops in an organized hemothorax and coats both the parietal and visceral pleural surfaces. This adhesive process traps the lung in position and prevents it from expanding fully. Persistent atelectasis of portions of the lung and reduced pulmonary function result from this process.
By far the most common cause of hemothorax is trauma. Penetrating injuries of the lungs, heart, great vessels, or chest wall are obvious causes of hemothorax; they may be accidental, deliberate, or iatrogenic in origin.  In particular, central venous catheter and thoracostomy tube placement are cited as primary iatrogenic causes. [6, 7, 8]
Blunt chest trauma can occasionally result in hemothorax by laceration of internal vessels.  Because of the relatively more elastic chest wall of infants and children, rib fractures may be absent in such cases. [10, 11]
The causes of nontraumatic or spontaneous hemothorax include the following:
Neoplasia (primary or metastatic)
Blood dyscrasias, including complications of anticoagulation
Pulmonary embolism with infarction
Torn pleural adhesions in association with spontaneous pneumothorax
Pulmonary arteriovenous fistulae
Hereditary hemorrhagic telangiectasia 
Nonpulmonary intrathoracic vascular pathology (eg, thoracic aortic aneurysm or aneurysm of the internal mammary artery)
Intralobar and extralobar sequestration 
Abdominal pathology (eg, pancreatic pseudocyst, splenic artery aneurysm, or hemoperitoneum)
Case reports involve associated disorders such as hemorrhagic disease of the newborn (eg, vitamin K deficiency), Henoch-Schönlein purpura, and beta thalassemia/hemoglobin E disease. [14, 15, 16, 17] Congenital cystic adenomatoid malformations occasionally result in hemothorax.  A case of massive spontaneous hemothorax has been reported with Von Recklinghausen disease.  Spontaneous internal thoracic artery hemorrhage was reported in a child with type IV Ehlers-Danlos syndrome.
Hemothorax has also been reported in association with costal cartilaginous anomalies. [20, 21, 22, 23] Rib tumors have rarely been reported in association with hemothorax. Intrathoracic rupture of an osteosarcoma of a rib caused hemorrhagic shock in a 13-year-old girl. 
Hemothorax has been noted to complicate a small fraction of spontaneous pneumothorax cases. Although rare, it is more likely to occur in young adolescent males and can be life-threatening secondary to massive bleeding. 
Quantifying the frequency of hemothorax in the general population is difficult. A very small hemothorax can be associated with a single rib fracture and may go undetected or require no treatment. Because most major hemothoraces are related to trauma, a rough estimate of their occurrence may be gleaned from trauma statistics.
Approximately 150,000 deaths occur from trauma each year. Approximately three times this number of individuals are permanently disabled because of trauma, and the majority of this combined group have sustained multiple trauma. Chest injuries occur in approximately 60% of multiple-trauma cases; therefore, a rough estimate of the occurrence of hemothorax related to trauma in the United States approaches 300,000 cases per year. 
In a 34-month period at a large level-1 trauma center, 2086 children younger than 15 years were admitted with blunt or penetrating trauma; 104 (4.4%) had thoracic trauma.  Of the patients with thoracic trauma, 15 had hemopneumothorax (26.7% mortality), and 14 had hemothorax (57.1% mortality). Many of these patients had other severe extrathoracic injuries. Nontraumatic hemothorax carries a much lower mortality.
In another series of children with penetrating chest injuries (ie, stab or gunshot wounds), the morbidity was 8.51% (8 of 94).  Complications included atelectasis (3), intrathoracic hematoma (3), wound infection (3), pneumonia (2), air leak for more than 5 days (2), and septicemia (1). Note that these statistics apply only to traumatic hemothorax.
At present, the general outcome for patients with traumatic hemothorax is good. Mortality associated with cases of traumatic hemothorax is directly related to the nature and severity of the injury. Morbidity is also related to these factors and to the risks associated with retained hemothorax, namely empyema and fibrothorax/trapped lung. Empyema occurs in approximately 5% of cases. Fibrothorax occurs in about 1% of cases.
Retained hemothorax with or without one of the aforementioned complications occurs in 10-20% of patients who sustain a traumatic hemothorax, and most of these patients require evacuation of this collection. Prognosis after the treatment of one of these complications is excellent.
Short-term and long-term outcome for individuals who develop a nontraumatic hemothorax is directly related to the underlying cause of the hemothorax.
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