Haemorrhage

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).

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.

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

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.

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.

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

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

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

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.

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

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 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.

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.

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

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.

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.