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The University of Tennessee

The College of Veterinary Medicine

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Portosystemic Shunts


Medical Treatment

Medical management of animals with PSS includes correction of fluid, electrolyte, and glucose imbalances and prevention of hepatic encephalopathy by controlling precipitating factors. Dietary protein is restricted to reduce substrates for ammonia formation by colonic bacteria. Gastrointestinal hemorrhage, another source of protein, should be controlled with ranitidine and sucralfate if gastric irritation or ulceration is suspected, and with antihelmintics if parasites are present. Non-absorbable intestinal antibiotics that are effective against urea-splitting bacteria, such as Neomycin, should be administered to decrease bacterial populations. Enemas and cathartics may be used to reduce colonic bacteria and substrates and are especially important in animals with hepatic encephalopathy. Lactulose, a synthetic disaccharide, is hydrolyzed in the colon to organic acids which increase fecal water loss osmotically and acidify colonic contents. Acidification will trap ammonia as ammonium in the colon and will alter colonic bacterial flora. Alteration of intestinal transit time associated with the osmotic diarrhea will decrease time available for ammonia production and absorption. Lactulose may be given orally or by enema; dosages should be regulated so that feces is soft but formed. Cystitis should be treated with appropriate antibiotics based on urine culture and sensitivity; response may be poor if uroliths are present. Urate uroliths may respond to low protein diets; renal calculi have reportedly dissolved after shunt ligation.

With proper medical management, weight and quality of life stabilize or improve with treatment in most animals.  One third of dogs do well with medical management as the sole method of treatment, with many living to 7 years of age or older. Duration of survival with medical management alone has been correlated to age at initial signs and with BUN concentration; dogs that are older at presentation or have a higher BUN live longer. Over half of dogs treated with medical management alone are euthanized, usually within 10 months of diagnosis, because of uncontrollable neurologic signs and, in some cases, progressive hepatic fibrosis and subsequent portal hypertension. Surgery is therefore considered to be the treatment of choice for animals with congenital PSS.

Anesthetic Treatment

Anesthetic agents which are metabolized by the liver (i.e. barbiturates and phenothiazine tranquilizers), highly protein-bound (i.e. diazepam and barbiturates) or hepatotoxic (i.e. halothane) should be avoided because of poor hepatic function and hypoalbuminemia. Mask induction and maintenance of anesthesia with isoflurane is often the anesthetic regimen of choice. Opioids can be used as a premedication since it is reversible. Intraoperative treatment with plasma, hetastarch, antibiotics, and steroids may be necessary.

 

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