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Portosystemic Shunt in Dogs

What is a liver shunt?

The liver takes in blood from the portal vein: a large vein which collects blood from the pancreas, spleen and digestive system, and carries it to the liver where toxins and other by-products are removed.

If an abnormal connection exists or forms between the portal vein and another vein - allowing blood to bypass around the liver - then a “liver shunt” is present.

A liver shunt is usually caused by a birth defect called a congenital portosystemic shunt. If multiple small shunts form because of severe liver disease such as cirrhosis then these are called acquired portosystemic shunts.



What are the clinical signs of a liver shunt?

Commonly-seen signs include undeveloped muscles, stunted growth, seizures and abnormal behaviours (circling, disorientation, zoning-out).

Less-common symptoms include excessive drinking or urinating, vomiting, and diarrhoea. Some dogs only begin to show signs as they get older, when they develop urinary problems such as recurrent bladder infections or kidney stones. Behavioural clinical signs may only be shown after eating meals with high protein content.

Dogs with a liver shunt often take a long time to recover from anaesthesia.

How is a liver shunt diagnosed?

  • Urinalysis. Urine may be diluted or contain evidence of an infection.

  • Complete Blood Count (CBC) and Serum Chemistries. Abnormal findings include fewer than normal red blood cells, increases in liver enzymes, and low blood urea nitrogen/albumin.

  • Bile Acid Test. Liver shunts in dogs can elevate bile acids in the blood.

  • Additional diagnostic tests may include: Ultrasound, CT scan, MRI scan, Exploratory surgery (laparotomy).

  • Certain breeds are more prone to portosystemic shunts: Yorkshire Terriers, Old English Sheepdogs, Irish Wolfhounds, Cairn Terriers, Pugs, French Bulldogs and Beagles are among these.


What is the treatment?

Dogs with portosystemic shunts can benefit from medications and special diets which attempt to reduce the amount of toxins in the large intestines. Severely ill dogs may require intravenous fluids to stabilize blood sugar, an enema to remove intestinal toxins, and anti-seizure medication.

The most common medical treatment regime includes diet change, the administration of lactulose (a pH-altering sugar), and antibiotics.


Dietary management

Due to the liver's role in metabolising many of the nutrients in the body, dietary management can be a highly effective way to manage the symptoms and long-term outlook in dogs with a portosystemic shunt. The main features of a diet suitable for dogs with this condition are as follows:


Protein Restriction

Many of the symptoms of liver disease are the result of the waste products of protein breakdown building up in the blood. There are several ways that we can alter the protein in your dog’s food to support liver disease and reduce symptoms.


High digestibility:

Undigested food that makes it to the large intestine is fermented by gut bacteria. The waste products of this fermentation process (ammonia, for example) can worsen neurological signs and nausea.

Providing a diet that is easily digestible (home-cooked diets are extremely digestible) reduces the amount of undigested food that reaches the large intestine.


Altered protein sources:

Vegetarian proteins like eggs and cheeses tend to be better tolerated by pets with liver disease, especially in cases where neurological signs have been a problem. It’s not uncommon that a diet made for a pet with severe liver disease is made primarily of carbohydrates and high quality vegetarian protein sources like egg.


Reduced overall protein intake:

Protein reduction is commonly helpful when managing liver disease in dogs.

The level of restriction required depends on the severity and type of liver disease. For most pets with problems of nausea or neurological signs they will require restricted protein of 20% by dry matter or less. Pets with chronic liver diseases or no other symptoms may still be able to have normal protein levels.

Protein restriction should ALWAYS be done carefully and by a professional: it’s important to still meet all minimum amino acid requirements to prevent other problems from occurring (like heart disease!)


Purine reduction

Purines are compounds that are present in many food types. Dogs with liver shunts often struggle to process these and as a result ammonium biurate (a type of purine urine stone) are more common in dogs with liver shunts.

Purine restriction is indicated in these pets to prevent urate stone formation. Urate stones do not dissolve so usually require surgical removal which makes them particularly dangerous.

Most meats are high in purines, especially offal. This means that most hepatic support diets will contain only small amounts of meat and will often be made mostly of vegetarian protein and carbohydrates/vegetables.


Taurine and Vitamin K

Both taurine and vitamin K undergo processing in the liver to become active. Pets that have a poorly-functioning liver may need supplementary levels of active vitamin K and taurine to ensure that they have enough.


B Vitamins

Many pets with liver disease urinate and drink more than normal and struggle to conserve water. Most of the B vitamins are water soluble and not stored well in the body. Therefore pets with liver disease require higher than normal levels of B vitamins in their diet.


Zinc

Zinc has many positive effects on the liver including enhancing ‘ureagenesis’ (processing the waste ammonia into urea that can be excreted more effectively). Dietary zinc levels for pets with liver disease are usually increased to around three times the normal minimum level.


Copper and Iron

Excess copper and iron can cause further liver damage so it’s important to keep levels controlled. Diets for pets with liver disease are carefully formulated to have lower copper and iron levels, whilst still providing sufficient levels to support normal function (e.g. red blood cell production).


Vitamin E and Antioxidants

Increasing the levels of vitamin E and antioxidants is important in supporting pets with liver disease. Supplements, diets and recipes should be formulated to have higher than usual vitamin E and C levels. Good sources are fresh fruit and vegetables.


Fibre

Nitrogen is a major part of the waste products that are responsible for the neurological signs in liver disease. Soluble fibre like those from apples (pectins) or lactulose (often used by vets) can be used to ‘fix’ nitrogen in the gut and prevent it from being absorbed into the blood.


What if my dog is a puppy?

Puppies with liver disease require even more specialised diets. Protein and mineral restriction must be done more carefully as puppies still need enough nutrients to grow.


What is the probable outcome with proper management?

With proper diet and medication most dogs will manage to live a normal-length life of good quality. Dogs that do well with long-term medical management are usually older at the time of diagnosis with more normal blood test values and less severe symptoms. If diagnosed as a puppy, the care can be challenging.


Summary of clinical recommendations for pets with liver shunts

When formulating diets for dogs with portosystemic shunts, the VetChef Nutritional team will work to the following clinical nutritional guidelines:

  • Protein level <20%DM if signs of neurological disease (hepatic encephalopathy) or ongoing nausea

  • Choose digestible vegetarian protein sources when possible

  • Zinc increased to 3x the usual minimum level (>20mg/100gDM)

  • Copper <0.5mg/100gDM

  • Iron 8-14mg/100gDM

  • Taurine 0.1%DM

  • Vitamin E 26.8mg/100gDM

  • Increased water-soluble B vitamins (The author suggests at least twice the minimum recommended allowance)

  • Soluble fibre added


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