Portosystemic Shunts

Congenital Portal Shunts are due to a defect in the blood circulation around the liver. Instead of blood entering the liver to be detoxified, the liver is bypassed. The liver usually eliminates toxins derived from the gut. With a porto-systemic shunt, there is a bridging between the veins around the liver and so the toxic material bypasses the liver, causing an elevation of ammonia in the circulation.


This defect may be within the liver (intrahepatic) or occur outside of the liver (extrahepatic) - most are single vessels.

Shunts can be congenital (present at birth) or acquired. Acquired shunts can develop subsequent to portal hypertension (high blood pressure); typically they are multiple in nature. This occurs due to a lack of valves in the portal vein, permitting circulatory accommodation through the shunt. Portal hypertension is usually associated with liver scarring or cirrhosis.

The shunt may lead to episodic development of hepatic encephalopathy (seizures or bizarre behavior) associated with ingestion of high protein food, and administration of certain drugs.

Another effect of the shunt is the development of bladder stones due to inability of the liver to metabolise uric acid from the blood.

SYSTEMS AFFECTED

Nervous system signs include episodic hepatic encephalopathy (seizures).
Gastrointestinal signs are intermittent inappetence; vomiting; diarrhea; pica; drooling in cats.
Urogenital signs bladder stones and or large kidneys

GENETICS

Basis unknown
Breeds predisposed include miniature schnauzers; Irish wolfhounds; Old English sheepdogs; cairn terriers; Yorkshire terriers

INCIDENCE/PREVALENCE

Incidence is greatest in purebred dogs and mixed breed cats
Especially common in Yorkshire terriers

CLINICAL SIGNS

Episodic seizures or disorientation (hepatic encephalopathy) may be noted.
Affected cats may drool. This may be initially confused with an upper respiratory infection based on the display of increased salivation.
Initial signs usually noted at initial feeding of puppy or kitten food and stunted growth is common

SYMPTOMS

CNS Signs: Episodic weakness, pacing, disorientation, head pressing, blindness, behavioral changes (aggression, vocalization, hallucinations), seizures, coma
Gastrointestinal Signs: inappetence, vomiting, diarrhea
Urinary Signs: bladder stones
Congenital disease –The pets may have a normal appearance or have stunted stature, hepatic encephalopathy, golden or copper irises in non- blue-eyed and non-Persian cats.

DIFFERENTIAL DIAGNOSES

CNS signs -Other rule outs include infectious disorders (e.g., FIP, canine distemper, toxoplasmosis, FeLV-related infections); toxicities (e.g., lead, mushrooms, recreational drugs); hydrocephalus; epilepsy; metabolic disorders (e.g., severe low blood sugar).
Gastrointestinal signs—bowel obstruction; dietary indiscretion; foreign body ingestion; inflammatory bowel disease
Urinary tract signs—bacterial urinary tract infection; stones

DIAGNOSIS

Lab Work

CBC/Biochemistry: low BUN, creatinine, glucose, and cholesterol common; liver enzyme activity variable (ALP usually high in young patients owing to bone isoenzyme); bilirubin normal with congenital but may be high with acquired shunts.
Urinalysis: Decreased urine specific gravity (inability of kidneys to work properly) and crystals in the urine.
Total serum bile acids—sensitive indicators; random fasting values may be within normal reference range; 2-hr postprandial (post feeding) values markedly high (usually > 100 mmol/L)
Blood ammonia values—sensitive indicators; less reliable than total serum bile acids because of analytic problems
Ammonia tolerance testing—more reliable than random ammonia values; samples cannot be stored, frozen, or mailed for analysis.

Imaging

Abdominal Radiography: Small liver, Large kidneys, Bladder stones
Injecting radiographic contrast media into a mesenteric or spleenic vein. This is the test of choice, but is technically difficult.
Abdominal Ultrasonography: Subjective estimation of small liver, hypervascularity, and observation of the shunting vessel. Color-flow Doppler—assists in shunt localization. Intrahepatic shunts are most easily imaged.


Acquired Shunts

Liver size depends on underlying cause.
Abdominal fluid is easily detected.
Ammonium urate calculi (stones) in the kidney or bladder

TREATMENT

Eliminate causal factors—dehydration; elevated kidney toxins; gastrointestinal bleeding; high- protein foods; infection (urinary tract, other); treatment with certain drugs

Protein-restricted diet—dogs: dairy and soy protein may perform better than meat and fish proteins; cats: require balanced, meat-based protein.

Increase dietary protein tolerance by concurrent treatment with lactulose (0.5–1 mL/kg PO q8–12h; dose based on production of two to three soft stools daily), metronidazole (7.5 mg/kg PO q8– 12h), and/or neomycin (22 mg/kg PO q12h).

Cleansing enemas with warmed isotonic fluids— until free of feces
Retention enemas—15 mL/kg; with lactulose (1:2 dilution with water) and neomycin (10–15 mg/kg)

SURGICAL CONSIDERATIONS

Surgical ligation with congenital disease

Goal: total ligation vessel; often only partial ligation can be performed safely and surgical assessment of extent of ligation may be inaccurate.

Hepatic encephalopathy signs must be resolved before surgery. Intrahepatic shunts are most difficult to ligate.

This article was donated by the Columbia Animal Hospital. For further information please visit http://www.petshealth.com/

A Healthy Diet for Dogs

Every owner these days seems to have their own ideas on what constitutes a healthy balanced diet for their dog. How many of them are reliably imformed though? The following questions are designed to critically assess your dogs diet. Please read them, for your dogs sake.

1) How many times a day do you feed your dog?

There is no set rule for adult dogs but the general consensus is that twice a day is a sensible amount. Some owners feed once a day, some three times a day. How much your dog is fed is far more important than how often really, but it is useful to set guidelines nevertheless. The reason many experts suggest twice a day rather than once a day is that once a day feeding encourages the dog to gorge his or her food as he or she is so hungry, having last had a meal a full 24 hours ago. Eating too quickly can cause reflex regurgitation or vomiting. Also it has been theorized that deep chested large breed dogs are more likely to suffer from a twisted stomach (gastric dilatation and volvulus), a life threatening condition, if they are fed one large meal daily rather than two smaller meals.

Clearly more active dogs will burn far more calories than others but these variables are best reflected in portion size rather than frequency. Some dogs with medical conditions may benefit from multiple meals of smaller portions, for example those recovering from gastroenteritis. Puppies must be fed more often than adult dogs as they have a higher metabolic rate, around 4 times a day from weaning to around 5 months old, then drop down to 3 times a day until 7 months old, then down to twice a day thereafter.

2) Is your dogs diet manufactured specifically for dogs or do you give human food or food from the butchers?

There is a misconception around that human food is higher quality than dog food, and therefore better for them. This is by and large nonsense. Reputable dog foods are formulated after extensive trials by pet food companies to provide the mixture of protein, carbohydrate and fat that suits canine physiology best. Dogs on balanced dog food diets do not get nutritional deficiencies but dogs on human food do. Certain human titbits can play havoc with your dogs digestive tract, chocolate being a prime example.

Your dog need ingest nothing other than a complete dog food and water to have a complete and balanced diet. Remember, dogs do not need variety in their diet! They are perfectly happy having the same boring looking meal every day! So keep it simple and safe, feed your dog either a complete dog food (dry or tinned, dry is better for their teeth) or standard dog biscuits and tinned dog meat together. Of course human leftovers every now and again or a bit of tripe or heart from the butcher is fine, but do not make it the day to day diet.

3) Which is the best dog food to choose?

There are so many different brands of dog food on the market, the best one is basically a matter of opinion. Certainly palatability is a factor, there is no point in purchasing a particular food if your dog cannot stand it, although this is occasionally a necessity in dogs with food allergies, for example. Rather than recommending you a specific brand, we suggest that you choose one which adheres to the criteria below.

Dog foods labeled as complete and balanced must meet standards established by the Association of American Feed Control Officials (AAFCO), either by meeting a nutrient profile or by passing a feeding trial. There are now two separate nutrient profiles for dogs - one for growth (puppies) and one for maintenance (adults). Maximum levels of intake of some nutrients have been established for the first time because of the concern that overnutrition, rather than undernutrition, is a bigger problem with many pet foods today. The standards include recommendations on protein, fat, fat soluble vitamins, water soluble vitamins, and mineral content of foods. If you are prepared to get technical, you should choose a food that comes closest to AAFCO recommendations.

In summary, consider the following points.

Choose a food that suits your dogs age, breed and overall health. Most big pet food companies will have different foods for small vs large breeds, and puppies vs adults. Dogs with medical conditions may be recommended special prescription diets.

Choose a food that come closest to AAFCO recommendations.

The ingredients contains the truth about a particular food. Everything else is there only for marketing purposes.

There are no legal and scientific definitions for the terms premium, super premium, quality, or natural.

Use dry matter numbers to evaluate and compare foods.

The source of ingredients (e.g. animal vs vegetable) does not matter, except in the case of food allergies.

Avoid supplementation. All commercial dog foods have more than enough protein, fat, vitamins, and minerals. Too many minerals can lead to severe skeletal problems in growing dogs.

Feeding your dog a good food incorrectly can lead to significant problems. For example, overfeeding puppies can lead to serious skeletal problems. Neutered dogs require portions 20% smaller than unneutered dogs or they will put on weight.

4) How many times a day do you give your dog treats?

It is hard to resist those puppy dog eyes begging you for a little piece of what you are eating. Indeed treats promote a special bond between you and your dog and it gives such pleasure when they have a delicious morsel to savor. The key word is MODERATION. If you are giving your dog regular treats, you must subtract this amount from the portion given at meal time to maintain a appropriate calorie intake. As a rule of thumb the amount of treats should never exceed 10% of your dogs daily food intake. It is far easier to make your dog obedient if you reserve treats for rewarding good behavior rather than just giving them willy nilly, where they become meaningless.

5) What do your dogs treats consist of?

Quality dog treats are usually far healthier and lower in calories than table scraps. Many dogs are fed scraps habitually from the table while families are eating, particularly by children. This only encourages further begging and feeding with often unsuitable high calorie treats which are forgotten about when it comes to measuring the dogs daily portion(s).

Matthew Homfray is one of the online experts at free pet Q&A service Televets. To ask a pet question visit http://www.televets.com