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Fluid in the Abdomen Fact Sheet

Information for pet owners on Fluid in the abdomen (Ascites) in dogs and cats.

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What is ascites?

Ascites is the medical term used to describe fluid accumulation in the abdominal cavity. Ascites is not a specific condition but a physical abnormality that develops as a consequence of an underlying disease.

The volume of fluid can vary between cases. A small volume may only be detectable on palpation of the abdomen or even with ultrasound. However, in some cases the volume can be large and the abdomen enlarges to give a pot-bellied appearance. This can also result in weight gain.

The type of fluid that accumulates can also vary depending on the underlying condition.

What can cause ascites?

Fluid in the abdomen can occur due to a variety of conditions, some require more urgent investigations and treatments than others. So, if your pet develops a pendulous, swollen abdomen we would advise an urgent assessment by your vet.

Examples of the groups of conditions that can cause ascites include:

  • Low blood protein levels – this can be associated with significant liver, kidney or intestinal disease
  • Heart disease – in particular heart conditions affecting the function of the right side
  • Infections – if due to a bacterial infection emergency surgery is required. In cats it can be caused by a viral condition called Feline Infectious Peritonitis (FIP)
  • Trauma can cause leakage of urine from the urinary tract or bleeding from an abdominal organ
  • Rat poison ingestion can cause clotting problems and result in bleeding into the abdomen
  • Cancers can cause fluid accumulations in a variety of ways. This can be due to bleeding from an organ, compression of blood vessels, inflammation due to the presence of the tumour or rupture of diseased organ

Note – unusual/ less common causes haven’t been listed

How is ascites investigated?

The approach can vary from case to case based on the findings of the physical examination and clinical history. For example:

  • A patient with ascites and diarrhoea would have investigations focused on the intestines and abdomen.
  • A patient with an abnormal sounding heart would have heart investigations.

It is not uncommon for these cases to require blood tests and imaging. However, a key component of the investigation is analysing a sample of the fluid in the abdomen. The type of fluid can narrow the list of possible causes.

How does abdominal fluid analysis help establish the cause of ascites?

The gross appearance of the fluid can sometimes give an initial impression of the potential underlying problem e.g. blood. However, often examination of the fluid under the microscope is required to assess the types of cells within the fluid. In addition, protein levels in the fluid are often measured.

Specialised testing of the fluid can be required in some situations and this can take time. Typically, these tests are not required in situations where urgent surgical intervention is needed e.g. organ rupture or bleeding. However, advanced testing at a specialist lab may be required if there is a suspicion of FIP or cancer.

What is the prognosis for patients with ascites?

Given the large range of possible causes of ascites, a prognosis can only be determined once an underlying diagnosis is reached. Surgery may be needed to manage some of the urgent causes of abdominal fluid. In other cases, the condition may be managed with medication. There are some conditions that cause ascites that are manageable or even curable. However, unfortunately some conditions may not be treatable.

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