Haemorrhagic Effusion

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Haemorrhagic effusions occur when blood leaks into a body cavity (the thorax, abdomen or pericardial sac). This occurs most commonly when a blood vessel is ruptured or eroded or when an organ ruptures. The fluid from acute haemorrhagic effusions resembles whole blood (with platelet clumps and leucocytes) but the fluid from more chronic effusions will not contain platelets, will not clot and will contain macrophages (or haemosiderophages) that have begun to phagocytose the haem pigment degradation product haemosiderin that is released from lysed red blood cells . Causes of haemorrhagic effusions include:

  • Traumatic rupture of a blood vessel or of an organ. The spleen is most likely to rupture after blunt abdominal trauma but the kidney or liver may also be affected. The presence of blood in the pleural cavity (haemothorax) may occur when fractured ribs lacerate blood vessels within the chest. Manual ablation of corpora lutea in cattle may also cause intra-abdominal haemorrhage and ovarobursal adhesions.
  • Haemangiosarcomas of the spleen may rupture, producing marked haemoabdomen.
  • Erosion of blood vessels may also be caused by neoplasia, allowing blood to enter a body cavity.
  • Idiopathic Haemorrhagic Pericardial Effusion refers to a type of haemorrhagic pericardial effusion with no apparent cause. It is most common in large breed dogs with a peak age of onset of 6 years.
  • Rupture of an atrial wall into the pericardial sac may occur with masses (particularly right atrial haemangiosarcomas), uraemia and with severe mitral valve disease.
  • Disorders of secondary haemostasis, including Haemophilia A or B, rodenticide toxicity, severe hepatic insufficiency and Angiostrongylus vasorum infection in dogs. Cattle which ingest dicoumarins (mycotoxins which act in a similar way to warfarin and other rodenticides) in sweet clover may develop haemorrhage from the umbilical vessels into the peritoneal cavity.
  • Haemorrhagic or serosanguinous peritoneal fluid may be found in colicking horses that have intestinal strangulation or obstruction. This finding may support a decision to manage the case surgically.
  • Iatrogenic effusions may occur after surgery, fine needle aspiration or biopsy of abdominal organs, especially in animals with coagulopathies.


Clinical Signs

Haemorrhagic effusions may occur in any of the major body cavities. In the abdomen, there may be signs of abdominal pain (due to the underlying cause of the effusion), an abdominal fluid thrill or a palpable mass, most commonly a splenic haemangiosarcoma.

In the chest, haemothorax may cause tachypnoea and dyspnoea if severe. Dullness will be evident on thoracic percussion if a pleural effusion has developed and the heart sounds will be muffled on auscultation.

Pericardial effusions may be sufficiently severe to cause cardiac tamponade and right-sided heart failure. The heart sounds will be muffled on auscultation and there may be hepatojugular reflux, a jugular pulse or signs of left-sided forward failure. Idiopathic haemorrhagic effusions do not usually clot and are therefore unlikely to result in restrictive pericarditis.

The loss of significant quantities of blood may cause pallor, tachycardia and tachypnoea, a haemic murmur, collapse and severe exercise intolerance.

Laboratory Tests

A haematological blood profile should be obtained to try to assess whether haemorrhage has occurred and whether a transfusion is required. If the sample is taken very shortly after the haemorrhage, there may be no changes on the haemogram as interstitial fluid will not yet have moved into the vasculature, diluting the remaining red blood cells. The following changes would be expected after an acute haemorrhage:

  • Reduced packed cell volume (PCV) or haematocrit (HCT).
  • Reduced haemoglobin concentration
  • Reduced plasma albumin or plasma protein concentration, a finding which is important to note as it allows the condition to be differentiated from haemolysis.
  • Reduced levels of platelets and all leucocytes (unless there is concurrent inflammatory pathology).

Signs of regeneration (increased mean cell volume (MCV) and polychromasia) would not be expected until 48-72 hours after the event in dogs.

Clotting times and a buccal mucosal bleeding time can be measured for detection of coagulopathies or thrombocytopathia (if the number of platelets is known to be normal). With acute rodenticide poisoning, the OSPT is often elevated initially because factor VII (part of the extrinsic pathway) has the shortest half-life of the vitamin K-dependent factors. Blood samples may be sent to specialist laboratories for measurement of levels of clotting factors (VIII and IX), von Willebrand's factor and proteins present in the absence of vitamin K (PIVKAs). Changes on a biochemical profile should indicate any severe hepatic disease and faecal samples can be collected for detection of Angiostrongylus vasorum if this is suspected.

Diagnostic Imaging

Effusions are easily diagnosed by ultrasonography and this modality may also be used to guide fine needle aspiration to obtain a sample of the fluid. As blood clots, the development of a granular texture should become evident as the fluid is scanned. Effusions also produce a distinctive pattern on plain radiographs:

  • With pericardial effusion, the heart may appear to be generally enlarged with a globular shape. There may be a crisp cardiac silhouette (as the heart is moving within a stationary bag of fluid) and a hypovascular lung pattern due to pulmonary underperfusion.
  • With ascites, there is a loss of serosal detail due to the presence of fluid in the abdominal cavity. This appearance may also occur with large abdominal masses and in emaciated animals. The shape, size and location of the spleen may be altered if it harbours a mass. If haemangiosarcoma is suspected, the heart should also be scanned as affected animals often have concurrent right atrial haemangiosarcomas.
  • With pleural effusions, the lung lobes are contracted and lobulation is evident. Areas of peripheral radio-opacity should be evident, especially peripherally in the chest. There may be signs of hypovolaemia, including a hypovascular lung pattern and microcardia.


Definitive diagnosis of any effusion relies on collection of a sample and cytological analysis. A refractometer can be used to measure the specific gravity of the fluid. The following features are typical of a haemorrhagic effusion:

Appearance Turbid, red fluid which may contain blood clots
Specific gravity 1.025 - 1.040
Total protein > 30g/L
Nucleated cells 1.5 - 10 x 10e9/L of which the WBC will derive from peripheral blood


In a case with ongoing haemorrhage, the source of this should be identified and techniques applied to achieve haemostasis. This may require an exploratory laparotomy and organ removal for bleeding abdominal masses. Care should be taken with trauma patients as they will often have multiple injuries. Animals with significant blood loss may require a transfusion of whole blood but the exact transfusion trigger depends on the chronicity and severity of the haemorrhage.

Coagulopathies are treated according to their cause. Factor VIII and Von Willebrand's factor may be supplemented with cryoprecipitate whereas animals with rodenticide poisoning should receive regular injections of vitamin K and intensive monitoring. Transfusions may be required if the bleeding cannot be controlled.

Pericardial effusions that are causing tamponade should be drained by pericardiocentesis but, if the effusion is recurrent, pericardectomy may be indicated.

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