We know about external bleeding because we can see it; we know how severe it can be. But hidden bleeding on the inside of our pets can be much more difficult to spot and just as serious.

What can cause internal bleeding?

A common example is after trauma. For example, after a car accident, an absence of physical blood does not rule out bleeding. Pets may still bleed into spaces out of sight; perhaps they may bleed into the brain after hitting the head, or from the spleen.

Small bleeds would usually be self-limiting because the blood forms a protective clot. But in large bleeds, a clot is not always sufficient. Further, in the event of the animal having a clotting disorder, this protective mechanism is completely removed. A common example is after the ingestion of anticoagulant rat poison. Even without a history of trauma, these patients can bleed into the guts, internal spaces or the skin (causing bruising) until they become severely – often fatally – weakened.

Tumours and the blood vessels within them are much more prone to bleeding than healthy vessels. A common example would be haemangiosarcoma on the spleen, which commonly leads to large amounts of blood loss into the abdomen. 

So what do we see on the outside when internal bleeding happens?

There are some common signs seen with any bleed:

Pallor – paleness

Ongoing or large bleeds can result in the pet running out of red blood cells and looking ‘pale.’ Vets are good at spotting this.

However, in the early stages after a bleed and before an animal looks pale, the spleen will often contract, releasing more red blood-cells into the circulation. Therefore not all animals with internal bleeding appear pale or even have low numbers of red blood cells; sometimes, they actually have a better colour! Luckily, a simple blood test can distinguish this kind of bleed.

Tachycardia – fast heart rate

If blood is lost from the circulation, the heart will have to beat extra fast to try to deliver what is left around the body. This can result in a weak, rapid pulse.


If the circulation is compromised to the point where blood can no longer be delivered around the body, for example to the brain. The lack of blood to the brain or lungs may result in collapse. 

The location of the bleed has a huge impact on any other symptoms that are seen 

The brain

Intracranial (within the skull) bleeds can happen after a head injury or as a result of a bleeding tumour. The brain is in a finite space within the skull, so bleeding within it tends to put pressure on the local brain tissue, affecting brain function. Different areas of the brain control different functions, so this can manifest in a variety of ways, including: circling, termours, inability to walk, dragging limbs, changes to eye direction, behavioral changes, confusion, tremors or fitting.

The guts

Bleeding into the guts manifests when the gut contents are seen, either being vomited up (fresh blood or ‘coffee grounds’ in vomit) or defecated (digested blood makes faeces look black). Technically, though, this isn’t ‘internal’ bleeding, as the gut can be classed as the outside of an animal, being linked as it is to the outside world at either end.

The abdomen

This one’s tricky, because there is a lot of space to bleed into in an abdomen. When a lot of bleeding has occurred, the abdomen may swell and feel ‘full.’ 

The retroperitoneal space

This is a little pocket of space tucked away behind the kidneys. Bleeding into this pocket can be hard to find and is usually found by an experienced ultra-sonographer.

The inside of the lungs

This manifests as difficulty in breathing and coughing up fresh blood.

Outside the lungs in the chest

This can manifest as shallow breathing, because the lungs cannot expand in their usual way. Breathlessness, a blue tinge to the gums, a lack of activity can all be signs.

Under the skin

Bleeds under the skin are usually called bruises and self-limiting because of the tightness of the skin. Sometimes, the bleed manages to form a lump – or haematoma – most common on ears.

Into the uterus

Menstruation is normal at certain stages of the cycle in females. However, blood can also collect here for other reasons.

The eye

This can usually be seen from the outside with an ophthalmoscope; it can be painful and affects the vision. It is also a very small space, so may not have such a large effect on the overall circulation. However, it can cause blindness.

So it can be seen that internal bleeding can happen in different places and manifest in a variety of ways. There is no one ‘symptom’ for internal bleeding.

What if my vet suspects internal bleeding?

They can do some simple tests on the blood (the haematocrit and total solids) which will help to confirm the suspicion. Because the signs of internal bleeding are so varied, they can easily be confused with signs of other disease. So this test has saved many lives.

Vets can also take pictures, such as radiography of the chest or ultrasonography of the abdomen (looking for free fluid sloshing around in there), to find out more information. Or place a needle into the abdominal cavity or chest to detect a build-up of free blood.

Then what?

The options depend on the location of the blood. Sometimes, for instance in a ruptured spleen, it makes sense to surgically find the cause of the bleed and remove it. Other times, for example bleeding into the brain, opening the brain cavity may do more harm than good.

The cause of bleeding is also important. For example, if bleeding is happening because the pet doesn’t have the required clotting factors, then bleeding will be generalized (in different locations). Giving a blood transfusion, with appropriate clotting factors, will often be more useful than surgery. 

Meanwhile, fluids are sometimes given to keep any remaining red blood cells circulating. Transfusions of Oxygen-carrying red blood cells may also be given to save lives.

What do I do if I suspect that my pet may be bleeding internally?

Any animal with weak, fast pulses, abdominal swelling or pale gums should be treated as an emergency and presented to the vet. After a car-accident, it is always worth considering a blood-test or scan to check for early signs of bleeding before the more severe signs are observed. 

What is the prognosis?

This depends on the animals’ circumstances, but there are two things to consider. The first is the likelihood of their surviving any treatment or surgery in the short term; the second is the long-come outcome. For example, if a bleeding tumour in an abdomen or chest has already spread, the owner may not want the vets to operate… Even if doing so might help the animal to survive initially. This is a conversation for the owner and vet. 

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