Portosystemic Shunts
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Article Written by Dr. Daniel A. Degner, Board-certified Veterinary Surgeon (DACVS)

Dr. Degner is currently employed at the

Animal Surgical Center of Michigan

Conveniently located in the Animal Emergency Hospital

1148 East Bristol Road

Burton, MI 48529


He will be seeing appointments and performing surgery very soon

For more information please call 810-671-0088

Key Points

A portosystemic shunt, therefore is an abnormal vessel that allows blood to bypass the liver. As a result the blood is not cleansed by one of the bodies filters: the liver.

Generally the bile acids levels (after feeding a meal) in patients having a shunt are higher than 100.

Surgery is the best treatment for a shunt

The overall success rate is about 85%

Shunt anatomy and physiology

  • In the fetus a shunt, called the patent ductus venosus, is present and bypasses blood away from the liver to the placenta so that the mother can cleanse the blood for the fetus. 
  • Once the fetus is born the shunt closes within three days after birth and the puppy's liver must clean the blood.  Sometimes the shunt does not close off. 
  • A portosystemic shunt, therefore is an abnormal vessel that allows blood to bypass the liver. As a result the blood is not cleansed by one of the bodies filters: the liver.
  • These dogs also have much less blood that flows to the liver which causes the liver to remain small.
  • There are many variations of congential portosystemic shunts that are found at surgery, however there two main groups:  shunts located in the liver (intrahepatic shunt) and shunts located outside of the liver tissue (extrahepatic shunt).  The intrahepatic shunt is most commonly found in large breed dogs and extrahepatic shunts are seen in small breeds. 
  • Above is a diagram showing the blood flow from the intestines, through the shunt (labeled) , then to the heart.  Most of the blood does not flow to the liver due to the resistance of the filters in the liver, thus the blood is not cleansed by the liver.


Clinical signs

  • Abnormal behavior after eating
  • Pacing and aimless wandering
  • Pressing the head against the wall
  • Episodes of apparent blindness
  • Seizures
  • Poor weight gain
  • Stunted growth
  • Excessive sleeping and lethargy
  • Straining to urinate due to bladder stone formation
  • Patient with a shunt may have many clinical signs and some have only a single clinical sign
  • Some dogs do not show signs until they are older



  • A variety of blood tests can be used to help to support a diagnosis of a portosystemic shunt.
  • Bile acid test are always elevated. Generally the bile acids levels (after feeding a meal) in patients having a shunt are higher than 100. Other diseases such as microvascular dysplasia, generalized liver disease, and acquired shunts due to liver cirrhosis can also cause elevated bile acids tests.
  • Sometimes the shunt can be identified with ultrasound imaging.
  • Nuclear scintigraphy is a fairly reliable test to ascertain whether a shunt is present, but may not be able to differentiate acquired from congenital shunts.
  • In most dogs we are able to identify the portosystemic shunt at the time of surgery.
  • Sometimes multiple acquired shunts, caused by end-stage liver disease are found; unfortunately no surgical therapy is useful to treat this (other than liver transplant, which is not practical in dogs).
  • If the shunt cannot be found at the time of surgery, dye is injected into one of the veins going to the liver and x-rays are taken (portogram). This will show the blood supply of the liver and the offending shunt, if it is present.  



  • If possible, we prefer to have the patient as stable as possible prior to surgery. This involves having your pet on a low protein diet and administering prescribed medication.
    • Antibiotics are used as bacteria, which are normally removed by the liver, by pass the liver and result in bacteria circulating in the blood.
    • Lactulose is a medication which traps toxins such as ammonia in the stool. It also decreases the transit time of the stool so that toxins are expelled quicker (thus the pet will defecate more often).
    • Low protein diet should be fed in order to decrease poisons that affect the brain.
  • Surgery is the best treatment for a shunt. Usually at the time of surgery the shunt can be identified (arrow showing large vessel) as is seen in photo below. 


  • For pets that have a shunt that is located outside of the liver, an ameroid constrictor ring is placed around the vessel (in photo below see metal ring). This device slowly closes the shunt over a period of 6 weeks.


  • If the shunt is located in the liver the surgery is much more complex. Because these shunts are usually found in large breed dogs, the shunt likewise is frequently very large. We have successfully used large ameroid constrictors for this purpose, but in some cases two surgeries are needed.


Potential complications

  • Complications can include high blood pressure (portal hypertension) of the vessels going to the liver, which results in fluid accumulation in the belly. If a high level of portal hypertension is present after the shunt is tied off, the pet will die.
  • About 15 % of the dogs having surgery will develop small-acquired shunts that basically function like the congenital shunt and thus the pet may need medical treatment for life.
  • Infection is an uncommon but possible complication.
  • Seizures may occur in the first 3 to 5 days after surgery.
    • Seizures can be caused by low blood sugar levels, which is easily treated
    • Seizures can be caused by the imbalances of the chemicals within the brain as the blood is being cleansed. These patients may die if they are not responsive to medication.


Postop care

  • After surgery your pet will still need to eat a low protein diet. Once bile acid levels (blood test) normalize a regular diet can be fed.
  • Lactulose and antibiotics are continued for about 10 days after surgery.



  • The overall success rate is about 85%. Usually the pet will start to feel better with 10 to 14 days after surgery.

Frequently Asked Questions After Surgery

When should my dog have the first bowel movement after surgery?

  • Many dogs will not have a bowel movement for the first 4 to 5 days after surgery
  • Reasons that a dog will not have regular bowel movements after surgery include:
    • The dog has been fasted prior to surgery
    • Dogs do not eat well during the hospital stay
    • They frequently do not eat well when they go home
    • They are fed highly digestible food that produces little stool
    • Pain medication that contain narcotics (such as morphine, fentanyl patches, and tramadol) can be constipating
  • If a pet does not have a bowel movement on the 5th day of being home, a stool softener such as metamucil can be fed
    • Dose of metamucil is 1 tsp per 25 Kg mixed in with each meal (canned dog food); feed immediately after mixing, as the metamucil will gel the food and may make it less palatable

My pet had surgery and will not eat.  What can be done?

  • Dogs
    • Most pets will not eat their regular dog food after surgery, especially if it is kibble.
    • Offer a cooked diet having a 1:1 ratio of a protein source and carbohydrate source.  The protein source can be any meat (example: chicken breast, turkey breast, lean hamburger) that is low in fat and should be cooked (drain off all fat after the meat has been cooked).   The carbohydrate can be pasta, potato or white rice.
    • Try canned dog food; to enhance the flavor sprinkle a very small amount of garlic powder or chicken or beef broth (Chicken-in-a- MugTM or Beef-in-a-MugTM products)
    • Try Gerber strained meats for babies such as the chicken, beef, turkey, or veal
    • Try Hill's A/D diet available at most veterinary hospitals
    • Hand feeding: place a small amount of food in the mouth so that your dog gets the flavor
    • Warm the food slightly in a microwave, as the food will be more aromatic; stir the food before feeding and test the temperature on the bottom side of your wrist; it should only be luke warm.
    • Remember that most pets will not eat the first day or two after they get home from surgery
  • Cats
    • Offer smelly foods that contain fish such as tuna or smelly cat foods
    • Try Gerber strained meats for babies such as the chicken, beef, turkey or veal
    • Hand feeding:  with your finger place a small amount of food on the roof of your cat's mouth; use a syringe to get soft food into the mouth
    • Warm the food slightly in a microwave as the food will be more aromatic; remember to stir the food before feeding and test the temperature; it should be only luke-warm
    • Some cats will only eat dry food, try kibble if your cat normally has been fed that food
    • Petting and stroking your cat frequently will help to stimulate appetite
    • Remember that most pets will not eat the first day or two after they get home from surgery
    • Appetite stimulants such as cyproheptadine may be helpful
    • If your cat refuses to eat anything for 7 days a stomach tube or nasogastric tube should be placed to provide nutrition so that a serious liver problem (hepatic lipidosis) does not develop

My pet is vomiting.  What can be done?

  • The first thing for you to discern is whether your pet is vomiting or regurgitating.  Both will result in fluid or food being brought up.  Vomiting always will have heaving or retching of the abdomen prior to expulsion of the vomitus.  Regurgitation is not associated with heaving and the pet usually just opens the mouth and fluid or food will be expelled.  Usually the regurgited material will be clear or brown colored fluid. 
  • Next is to identify the cause of the vomiting or regurgitation.
  • Causes and treatment of vomiting after surgery
    • When some pets return home after a stay in the hospital they may drink excessive amounts of water at one time and then vomit; if this appears to be the case, the water should be limited to frequent smaller amounts.
    • Medications such as antibiotics, narcotics or nonsteroidal anti-inflammatory medication commonly cause vomiting after surgery.  In order to see which medication is causing the problem, the administration of each drug should be separated 2 hours apart.  Usually the pet will vomit or appear nauseated (drooling and sick look) within 1 hour of administration of the medication that they are sensitive to.  The antibiotic in some cases may be changed to a different one, or may be discontinued. 
    • Stomach upset from anesthesia is a potential cause of vomiting and will pass within a couple of days. 
    • An uncommon cause of vomiting after surgery is internal organ failure.  Blood testing will confirm this problem. For this reason vomiting should not be ignored if it persists for more than 24 hours.
    • If your pet had surgery of the bowels or stomach, vomiting is always a concern, as it may indicate that infection of the abdominal cavity, called peritonitis, is present.  Do not ignore this sign.
    • Symptomatic treatment of vomiting involves withholding food for 12 to 24 hours, then introducing small amounts of bland food such as rice and lean cooked hamburger, if your pet does not vomit after that then gradually wean him/her back onto the regular diet after 3 days.  In order to decrease the acidity of the stomach, Pepcid AC 0.5 mg/kg can be given by mouth twice daily for 5 days.  Metoclopramide and Cerenia are good anti-vomiting medications for dogs and cats.  You should always consult a veterinary healthcare professional before administering medication.
  • Causes and treatment of regurgitation after surgery
    • The most common cause of regurgitation is reflux of acid from the stomach into the esophagus while your pet is under anesthesia.  Acidic fluid from the stomach can cause a chemical burn of the esophagus and result in a bad case of heart burn, called esophagitis.  This results in poor motility of the esophagus, therefore water and food will accumulate in this structure.  In most cases, esphagitis is self-eliminating and will resolve within two or three days. 
    • If the esophagitis is severe the esophagus may develop one or more strictures.  A stricture is a narrowing or stenosis of the esophagus and does not allow passage of food down the esophagus, in regurgitation that lasts longer than one week.  This problem should be brought to the attention of your pet's doctor within the first two weeks so that it can be treated by ballooning the stricture (minimally invasive procedure, as it is done with the aide of an endoscope).  If an esophageal stricture is chronic surgery is needed.
    • Symptomatic treatment of regurgitation caused by esophagitis includes feeding bland food, and administering a coating agent (sucralfate) and an acid blocker (omeprazole or other).  Consult a veterinary health care professional if the regurgitation continues for more than a couple of days.

How do I know that my dog is in pain following surgery?

  • Signs of pain include
    • crying
    • biting if you get near the surgical site
    • grimacing (lips are pulled back and the the dog looks anxious)
    • tragic facial expression
    • panting
    • restlessness and unable to sleep; pacing
    • if abdominal surgery was done the pet will not lie down on the incision, or will continually sit up in spite of appearing very tired
    • the worst pain will be for the first 2 to 3 days after surgery

What can I do to control my dog's pain?

  • Narcotic medications that control pain: tramadol, butorphanol, Duragesic (fentanyl patch)
  • Anti-inflammatories used to control pain: Deramaxx, Rimadyl, Previcox, or Etogesic
  • If an orthopedic surgery has been done cold packing the surgical site may be helpful
    • A cold pack may be a pack of frozen peas, crushed ice in a Ziploc bag, or a cold gel pack; place a thin barrier between the skin and the cold pack.  An alternative to a cold pack is to freeze water in a styrofoam cup; after frozen cut the bottom of the styrofoam cup out. Cool the surgical site around the incision by rubbing the exposed ice directly on the skin in a circular pattern.  Cooling the surgical site helps to numb the area.

How do I know that my cat is in pain following surgery?

  • Pain is more difficult to assess in cats versus dogs, as signs can be more subtle and they usually do not vocalize when in pain
  • Signs of pain in a cat include the following:
    • biting if you get near the surgical site
    • growling or deep cry
    • not wanting to eat
    • hiding and not wanting to be near owner (remember that this could also be caused by the cat just being upset about leaving home and coming back)

What can be done for pain at home for my cat?

  • Pain medication such as buprenorphine or a Duragesic (fentanyl) patch
  • Tylenol will kill a cat as they lack abundant glutathione enzyme in the liver
  • Anti-inflammatories can be used, but the dose is much less than dogs

Is it okay for my pet to lick the incision?

  • If a dog licks the incision, the healing process may be delayed.
  • Licking can remove stitches and cause the incision to open
  • Licking can become a severe habit that is difficult to break
  • Licking can cause infection as the mouth has many bacteria
  • Dogs will frequently lick the incision when the owner is not watching such as at night time; if the skin looks red or excoriated the most common cause is from licking.
  • To stop your pet from licking the following can be tried:
    • Elizabethan collar can be placed on the neck; this will not help stop your pet from scratching at the region
    • Cervical collar (bite not collar) is a less awkward device and can be effective at stopping a pet from licking the surgical site
    • A tee shirt can be used to cover an incision on the chest or front part of the abdomen; gather the waist of the shirt up over the dog's back and wrap an elastic band around this part of the shirt.
    • A bandage or sock can be used to cover an incision on a limb; fasten the top of the sock to the dog's limb with tape.
    • Bitter apple can be applied around the incision; many dogs will continue to lick  after application of this topical
    • Bitter Apple and Liquid HeetTM (obtain this from a drugstore...it is used for sore muscles) mixed in a 2:1 ratio can be applied around the skin incision
    • Antipsychotic medication in some cases is needed

Board-certification by the American College of Veterinary Surgeons

What does it mean?

  • Four years of advanced training in surgery beyond the Doctor of Veterinary Medicine Degree

  • Experience in the development of new surgical treatments

  • Rigorous examination by the American College of Veterinary Surgeons to ensure competency in advanced surgical techniques

  • Assurance that a veterinarian is a surgical specialist

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