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  • Hemothorax describes free blood within the pleural cavity with a packed cell volume (PCV) similar or higher than that obtained from a blood sample.
  • Hemomediastinum describes blood contained within the mediastinum and can occur in conjunction with or separately from a hemothorax.
    The term hemothorax has also been used in the literature to describe effusions with a PCV lower than blood. The boundary between a sanguinous effusion and hemothorax with regard to PCV is somewhat blurred.
  • Cause: wide variety of causes including trauma, neoplasia, hemostatic dysfunction/coagulopathy.
  • Signs: muffled heart and lung sounds on thoracic auscultation, hypovolemic shock, dyspnea/respiratory distress/tachypnea, lethargy, cyanosis, malaise.
  • Diagnosis:
    • History.
    • Clinical examination.
    • Thoracocentesis (PCV and TP of fluid and submit for cytology).
    • Radiography (dorsoventral, right and left lateral, horizontal beam or hanging lateral).
    • Clotting/Coagulation Profile.
    • Hematology and Biochemistry (including PCV, TP, electrolytes, urea and creatinine).
    • Ultrasonography of abnormal lung lobes.
  • Treatment: Airway, Breathing, Circulation approach to the collapsed patient, therapeutic thoracocentesis with thoracic drainage to relieve dyspnea, specific treatment for underlying condition, eg rodenticide poisoning.




  • The majority of blunt thoracic trauma Thorax: trauma patients do not develop hemothorax, but potentially serious bleeding can occur from damaged intercostal, internal thoracic or other vessels caused by the sharp ends of rib fractures Thoracic wall trauma.
  • Diaphragmatic rupture Diaphragm: traumatic hernia can also result in hemothorax in its acute stages.
  • Laceration of vessels or lung parenchyma by thoracic penetrating or gunshot wounds often result in hemothorax combined with pneumothorax Pneumothorax.


  • Iatrogenic damage to the intercostal or internal thoracic vessels should be avoided if at all possible and meticulous hemostasis is essential when performing thoracic surgery.
  • Tamponade (pressure build up) in the region of the bleeding vessel does not occur so clots do not form.
  • Incorrect technique for thoracocentesis or retraction of a bleeding artery or vein into the thorax during forequarter amputation can also cause potentially serious hemothorax.
    Failure to deal with even seemingly innocuous low pressure hemorrhage can lead to serious blood loss due to the large space provided by the thoracic cavity.

Hemostatic dysfunction

  • Secondary clotting cascade disorders involving the extrinsic, intrinsic or common clotting pathways can result in significant spontaneous or trauma induced hemothorax or hemomediastinum.
  • Causes of secondary clotting cascade abnormalities can include Warfarin /Coumarin poisoning, disseminated intravascular coagulation (DIC) Disseminated intravascular coagulation , liver failure, parasites, heparin overdose, and hemophilia.


  • Spontaneous thymic hemorrhage has been reported in dogs less than 2 years old.
  • The condition is rare, usually fatal and can occur in all breeds though the German Shepherd Dog and Cocker Spaniel seem over-represented.
  • Hemorrhage occurs from weak walled vessels following minor trauma (eg stopping suddenly on a lead) or a period of raised blood pressure.

Thoracic masses

  • Bleeding with or without effusion from primary or metastastatic masses within the lung parenchyma or thoracic wall can occur (eg squamous cell carcinoma Skin: squamous cell carcinoma , adenocarcinoma Adenoma / adenocarcinoma , hemangiosarcoma Hemangiosarcoma , osteosarcoma Osteosarcoma , etc) or hemomediastinum (eg heart base hemangiosarcoma, chemodectomas, thymoma Thymoma ).
  • Invasion of blood vessels by thyroid carcinoma Thyroid gland: neoplasia has been reported as a cause of hemothorax and hemomediastinum.
  • Erosion of blood vessels by infectious processes causing thoracic abscesses should also be considered.

Esophageal foreign body

  • Damage to blood vessels caused by sharp esophageal foreign bodies Esophagus: foreign body can cause hemothorax or hemomediastinum.
    Extreme care must be exercised when removing such objects, particularly in the region of the heart base.

Lung lobe torsion

  • Continued arterial flow with collapse of venous drainage due to lobe torsion Lung: lobe torsion can raise the hydrostatic pressure enough to cause bleeding from the surface of the torsed lung parenchyma in addition to effusion associated with the condition.

Mechanical vessel abrasion

  • Rib cartilaginous exostoses or malignant bone neoplasms have been reported as a potential cause of hemothorax in man due to the abrasive, irregular lesion rubbing on vessels during respiration.


  • Osteosarcoma and chrondrosarcoma Chondrosarcoma are rib masses that can invade through the interal thoracic arteries or the intercostal vessels that can cause hemothorax, with or without trauma. These forms of neoplasia are more common in young dogs, sometimes less than 1 year of age.

Predisposing factors

  • Primary clotting disorders (thrombocytopathia, thrombocytopenia, von Willebrands Disease (VWD Von Willebrand's disease )) characterized by petechiae and ecchymoses are unlikely to result in significant spontaneous bleeding into body cavities. However, their inclusion on a differential list is warranted due to the risk of increased hemorrhage in these animals following trauma.


Hypovolemic shock

  • Acute loss of more than 10-20 % of circulating volume results in death without adequate hypovolemic shock therapy.
  • A 4 kg cat has a circulating blood volume of approximately 240 ml. Therefore this average cat can only afford to lose approximately 20-50 ml of blood into the thoracic cavity before heroic resuscitation and cessation of blood loss would become necessary to avoid death.
  • A 25 kg dog would only need to hemorrhage 200-500 ml before severe hypovolemic shock would become apparent.
  • The volume available in the pleural cavity of dogs and cats will easily accommodate enough blood to cause death from hypovolemia before tamponade builds to stop bleeding. Therefore, in the majority of cases, hypovolemic shock caused by true hemothorax would need to be from a slowly leaking vessel in order to allow time for the animal to be presented to a veterinary hospital and successfully treated.


  • Anemia Anemia: overview following trauma in a patient may be due to bleeding from intercostal or other thoracic vessels. The hemorrhage is usually self-limiting if it is not severe enough to cause rapid exsanguination. Nevertheless, patients with rib fractures and evidence of anemia secondary to a bleed into the thoracic cavity should be monitored carefully with regular assessment of total protein Blood biochemistry: total protein and PCV Hematology: packed cell volume to ensure that the hemorrhage has abated.
  • Anemia is a common finding with other causes of slow intrathoracic hemorrhage including coagulopathies.


  • As for any pleural effusion Pleural: effusion or pneumothorax Pneumothorax , hemothorax can theoretically cause dyspnea and tachypnea due to the reduction in lung volume and resultant V:Q mismatch Ventilation-perfusion mismatching.
  • Ventilation impairment will not occur until 30 ml/kg blood has accumulated in the pleural space (Cockshutt 1995) by which time hypovolemic shock will have occurred.
    Hemothorax should be present on the differential list for pleural effusions associated with dyspnea since an effusion with a PCV lower than that of whole blood may still be termed hemothorax.
  • Cases with a slowly developing hemothorax may accumulate enough hemothorax to show significant dyspnea (Case example).

Pleuritis / pericarditis

  • Hemoglobin is a recognized adjuvant for the development of septic peritonitis and therefore has the potential to exacerbate intra-pleural infectious processes.
  • The presence of chronic hemothorax can cause pleural and pericardial reaction and fibrosis leading to secondary clinical effects linked with these processes.


  • Rapid hemorrhage will result in acute collapse after injury.
  • Chronic hemorrhage can result in onset of signs over days.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Cockshutt J R (1995) Management of fracture associated thoracic trauma. Vet Clin N Am Small Anim Pract 25 (5), 1031-46 PubMed.

Other sources of information

  • Macintire D K, Drobatz K J, Haskins S C & Saxon W D (2005)Respiratory Emergencies.In:Manual of Small Animal Emergency and Critical Care Medicine. Lippincott, Williams & Wilkins, Philadelphia. pp 138.
  • Monnet E (2003)Pleura and Pleural Space.In:Textbook of Small Animal Surgery. 3rd edn. Slatter D (ed). Saunders, Philadelphia. pp387-405.
  • Wingfield W E & Raffe M R (2003)Hemothorax.In:The Veterinary ICU Book. Teton Newmedia, Wyoming. pp 658-665 & 949.

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