High Blood Pressure in the Portal Vein to the Liver in Cats


PetMD Editorial

Updated Aug. 24, 2022

Portal Hypertension in Cats

When ingested food enters into the intestinal tract, the nutrients and toxins that are a part of the food that has been ingested are released into the digestive blood stream. Before this blood can flow into the systemic blood stream, it must first go through a filtering and detoxification process. The filtering process is carried out mainly by the liver, which detoxifies the blood and sends it out into the main circulatory system. The portal vein, the main part of the hepatic portal system, carries this deoxygenated, prefiltered blood from the digestive tract and its related organs (i.e., the spleen, pancreas and gallbladder) to the liver for processing. When blood pressure in the portal vein reaches a level that is greater than 13 H2O, or 10 mm Hg, this is referred to as portal hypertension. The two main causes of portal hypertension are increased portal flow, or increased resistance to blood.

Increased portal flow occurs when the portal veins attach to arteries, as they do in an arteriovenous fistula (where a new passage is formed between a vein and an artery), or it can occur as a result of blood being diverted (shunted) from the arteries to the liver. Increased resistance to blood can occur in the portal vein prior to its entry into the liver (prehepatic); in the portal vein inside the liver (hepatic); or, it can occur in the hepatic veins in the inferior vena cava (the largest vein in the body, which feeds blood from the lower body to the heart), after blood has exited the liver (posthepatic).

Whether due to increased portal blood flow, or to increased resistance to blood, portal hypertension can cause the formation of multiple portosystemic shunts (PSS), a condition in which the circulatory system bypasses the liver. Cats with portal hypertension can also develop increased abdominal lymph production, leading to fluid build-up in the abdomen. Even more critical is the development of hepatic encephalopathy, which manifests as seizures and problems with mobility due to the unfiltered toxins being delivered to the brain through the bloodstream.

Symptoms and Types

  • Yellow skin and eyes (jaundice)
  • Abdominal distention
    • Secondary hepatic encephalopathy
    • Seizures
    • Disorientation/confusion
  • Heart problems
    • Cough
    • Exercise intolerance
    • Trouble breathing
  • Portal vein blocked by a blood clot
    • Bloody diarrhea
    • Abdominal pain
    • Lack of energy
    • Lack of appetite


  • Portal vein
    • Blockage by a clot, narrowing
    • Compression
      • Large lymph nodes
      • Cancer
    • Postoperative complication of portosystemic shunt repair (reparation of diverted blood flow)
    • Small, closed, or blocked portal vein (called atresia); may be congenitally formed
  • Liver Disease
    • Chronic bile duct obstruction (in the ducts outside the liver)
    • Hepatic fibrosis (fibrous tissue growths on the liver)
    • Cirrhosis of the liver
    • Cancer
    • Chronic Inflammation
    • Hepatic arteriovenous fistula
  • Post-Hepatic
  • Congenital (present at birth)
  • Acquired


Your veterinarian will perform a thorough physical exam on your cat, including a blood chemical profile, a complete blood count and a urinalysis. You will need to give a thorough history of your cat's health leading up to the onset of symptoms.

Other important tests that your veterinarian will order are tests for total serum bile acids, blood ammonia levels, and a sampling of abdominal fluids. Testing the abdominal fluid is essential for determining where the cause of the portal hypertension is originating.

Internal imaging will also be a part of the diagnostic procedures. Results of chest x-rays may show that it is a heart disorder causing the portal hypertension, while abdominal x-rays will allow for a more exact examination of the spleen and liver. An abdominal ultrasound is invaluable for diagnosing disease. In addition, an echocardiogram can assist in diagnosing heart disorders, clots (thrombi), or protrusions in the walls of the abdomen (hernia). Your veterinarian can also use a diagnostic technique by which the internal anatomy is illuminated by using an injected radioactive tracer. This technique is used for a colorectal scintigraphy, where the colon is examined for abnormalities, and for a portovenography, which allows for examination of the portal system, and which can confirm whether there is a portosystemic shunt (PSS) – i.e., a diversion of blood flow. In simple terms, the radiopaque injection (tracer) will allow your doctor to visually examine the blood flow, and see whether the blood is passing through the liver to be filtered and detoxified, or whether the blood is being shunted – diverted – around the liver, creating a toxic condition for the entire system. Angiography, another imaging process using this technique, will allow your doctor to confirm possible abnormal openings and passages (arteriovenous fistulae) in your cat's liver by visually tracing blood flow through the arteries and veins. A sample of tissue may also need to be taken from the liver (liver biopsy), if liver disease is suspected.


Your cat will probably be hospitalized for monitoring and for fluid therapy, since dehydration and fluid retention are causes for concern. Your cat's system will need to be detoxed to prevent critical damage to the brain and system.

Surgery may be necessary, but it is dependent on the underlying cause of the disease. If your cat has abdominal fluid build-up, your veterinarian will also prescribe diuretic drugs to treat this.

Living and Management

After your cat has been discharged from care, you will need to restrict its activity until the abdominal swelling has resolved. Dietary changes may be in order, but you will need to consult with your veterinarian before making any major changes to your cat's meals. For example, if your cat is suffering from abdominal distention, it may need to be on a low salt diet to mitigate the fluid retention, but if your veterinarian wants your cat to have more fluid intake with increased urination so that the system will clear, dietary indications will be different. If your cat is diagnosed with hepatic encephalopathy, your doctor will likely recommend a low protein diet, until the liver is at full functioning ability, but again, do not make these changes unless they are recommended by your doctor. Your veterinarian will plan follow-up care based on the underlying disease.

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