Haemorrhage

()Map GENERAL PATHOLOGY (Map) CIRCULATORY DISORDERS

Introduction

• Haemorrhage is the escape of blood from within the cardiovascular system.
• Can be distinguished microscopically from congestion.
  • Congestion - the blood remains within the vessels.
  • Haemorrhage - blood is seen outside the vessels.
• Haemorrhage may be of capillary, venous, arterial and rarely cardiac origin.
• May be external or internal (within body cavities).
• Associated with:
  • Wounds or trauma.
  • Inflammation, where toxins are involved.
  • Neoplastic disease.
• "Haemorrhagic diathesis" describes a predisposition to bleeding, either spontaneous or associated with trifling mechanical damage.
  • Often manifests as purpuric disease.
  • Haemorrhagic diatheses and purpura may be a feature of a number of diseases of different aetiology (poisoning, septicaemia or neoplastic disease).

Types of Haemorrhage

• Two main types of haemorrhage are recognised and are considered in more detail below:
  • Rhexis
    • Actual physical rupture of a vessel wall
  • Diapedesis
    • The escape of blood from vessels.
    • It may be difficult to detect a disruption to the vessel wall.

Haematoma

• A large blood clot within the tissues.
  • A localised collection of blood confined by surrounding tissues resulting in a modular formation.
• Often sub-cutaneous.
• May form space-occupying lesions.
  • E.g. in brain.

In Body Cavities

• Haemothorax, Haemopericardium and Haemoperitoneum.
  • Blood escapes into the respective body cavities.

Petechiae

• These are minute - foci are 1-2mm in diameter.
• Of capillary origin.
• Usually seen on the skin, mucous membranes and serosal surfaces.

Ecchymoses

• Of capillary origin. .
• Foci are 3-23mm in diameter.
• Are blotchy.
• Often confluent.
• Usually seen on the skin, mucous membranes and serosal surfaces.

Purpura

• Purpura is a clinical syndrome.
• Multiple small spontaneous haemorrhages develop in tissues (e.g. skin, mucosae, serosal surfaces and joints).
• A mixture of petechiae and ecchymoses.

Haemorrhage by Rhexis

• This is of venular or arteriolar (or larger vessel) origin.
  • Results in major bleeding.
• There are several causes of haemorrhage by rhexis.
  • Trauma.
  • Haemorrhagic enteritis.
  • Erosion of blood vessels by tumours or abscesses.
  • Idiopathic rupture of arteries.
• In the horse intrapericardial rupture of the aorta may occur, although this is uncommon.

Haemorrhage by Diapedesis

Septicaemia

• Causes large numbers of petechiae and ecchymoses.

Toxaemia and Poisoning

• Causes petechiae and ecchymoses.
  • These haemorrhages are probably due to direct damage to the vessel walls.

Purpura haemorrhagica

• Pupura haemorrhagica is a condition that occurs in horses after an infection.
  • Particularly following Strangles.
• Endothelial damage is caused by accumulation of immune complexes.

Haemophilia

• Failure of the normal clotting of the blood.
  • Due to absence of one of the clotting factors.
• Rare.
• Reported in dogs and pigs.

Dicoumeral poisoning

• Dicoumeral is an antagonist to Vitamin K.
  • Vitamin K is needed by the liver to synthesise prothrombin and various clotting factors.
• Occurs with:
  • Warfarin poisoning
    • Warfarin is a common rat poison)
  • Prolonged feeding of sweet clover.

Gross Appearance of Haemorrhage

• The gross appearance of haemorrhage can vary depending on the tissue in which it occurs.

Epistaxis

• Epistaxis is a nose bleed.
• The haemorrhage may originate anywhere in the respiratory system.
• Can occur in the lungs following heavy exercise in the horse.
  • Appears bright red and perhaps frothy.

Gastric Haemorrhage

• Gastric secretion soon turns the blood a dark brown.
• When vomited up it is called Haematomesis.
• Blood originating in the stomach and upper small intestine that is passed through the anus and is called Melena.

Dysentery

• Occurs when the bleeding is low down the alimentary tract.
• The blood is passed in the faeces relatively unchanged.

Haematuria

• Blood is present in the urine.
  • Imparts a red colour to it.
• It is important to distinguish this from haemoglobinuria.
  • In haemoglobinuria, the breakdown products of red blood cells appear in the urine following intravascular haemolysis.
  • In haemorrhage, the red blood cells will separate out and sediment to the bottom of a test tube.

Bruising

• Brusing is the result of haemorrhage.
• Appears red for 48 hours and then begins to turn yellow.
  • Due to macrophages converting haemoglobin into haemosiderin.

Effects of Haemorrhage

Local

• Haemorrhage may result in a diffuse mass of red blood cells and fibrin in loose connective tissues and in organs.
  • E.g. in the cutaneous connective tissues, the spleen and the gut wall.
• Alternatively, a local accumulation may form a haematoma and become a space- occupying lesion.
  • This may interfere with organ function.
    • E.g in intracranial haemorrhage, haemopericardium, and pulmonary haemorrhage.

Systematic

• The systematic effects of haemorrhage are usually associated with uncontrolled blood loss.
  • I.e. from a major artery associated with trauma.
• Rate of loss is critical, e.g.
  • Loss of 30-40 per cent in a few minutes is often fatal.
  • Loss of over 50% over a 24 period may be tolerated in the dog.