Page 749 - Clinical Small Animal Internal Medicine

66 Portosystemic Shunts and Microvascular Dysplasia 717

features on liver biopsy in the absence of another hepatop- There is evidence that patients with liver disease are at
VetBooks.ir athy that could explain the biochemical perturbations are increased risk for gastrointestinal ulceration, and anec-
required for definitive diagnosis of PVH‐MVD.
dotal reports of this being a particular problem in dogs
with intrahepatic shunts. Therefore, many clinicians
Therapy include some type of antacid medication (H2 receptor
antagonist or protein pump inhibitor such as famotidine
or omeprazole) as part of the standard medical manage-
Medical Therapy
ment protocol. Finally, emerging evidence also sug-
Medical therapy is aimed at ameliorating the signs of gests that inflammatory cytokines are synergistic with
HE by reducing the amount of ammonia (and other sub- ammonia in precipitating HE and that controlling
stances) produced in the gut, and the degree to which inflammation in other organs is an important part of
they are absorbed. Medical management is often managing the patient with HE.
employed in those animals that show few clinical signs on
presentations, are older, in which financial or owner-lead
reasons limit surgery, or which have a shunt that is not Surgical Therapy
amenable to ligation. The main aims of therapy are to
decrease the formation of gut derived encephalotoxins, Surgical therapy is indicated for patients with CPSS, or
especially ammonia. Therefore the mainstays of current hepatic arteriovenous fistulae, where the primary prob-
therapy are a combination of dietary alterations, oral anti- lem can be resolved. Patients with acquired shunts sec-
biotics to suppress bacterial populations that produce ondary to end‐stage liver disease or PVH are unlikely to
encephalopathic toxins and local acting agents to reduce benefit from surgical attenuation of their shunts as the
gastrointestinal uptake of ammonia (e.g. lactulose). shunts are providing a mechanism for decompressing
Controlled trials have not been performed in animals to the portal system and reducing portal hypertension.
determine the optimal treatment for HE and so current Dogs with PVH-MVD, and those with portal vein apla-
recommendations are based on anecdotal evidence. sia, are also not candidates for surgical intervention.
Feeding a high‐quality digestible diet is the mainstay of However, the results of liver biopsy may inform medical
management of the stable patient. Protein restriction is management in patients with acquired liver disease, and
controversial, and generally not recommended, as some this often provides justification for surgical exploration.
authorities report that dogs with CPSS actually have nor- Surgical therapy for CPSS is aimed at identifying the
mal to increased requirements. If protein restriction is shunt and attenuating it. As most patients have poorly
required, a commercial restricted protein diet is the easi- developed hepatic portal circulation and relatively high
est to prescribe. For clients who wish to formulate their portal vascular resistance, total immediate occlusion of
own diet, protein sources should be easily digestible and the shunt is highly likely to result in life‐threatening por-
metabolizable. Vegetable and dairy proteins tend to be tal hypertension. Therefore, surgical methods aim either
better tolerated than meat‐based ones, with cottage to provide partial occlusion (which may be increased in
cheese being a palatable option for many patients. Cats stages by subsequent procedures) or application of a
have more stringent dietary requirements than dogs, and device to promote slow occlusion. The goal of slow or
this should be taken into account when choosing a diet. staged occlusion is to allow the intrahepatic portal circu-
Patients with reduced hepatic mass will have poor glyco- lation time to regenerate, with reduction in vascular
gen reserves and a tendency toward hypoglycemia, so resistance, at the same time as the shunt is being slowly
meals should be given frequently. or incrementally occluded.
Lactulose is prescribed for symptomatic patients, with The main techniques used for slow occlusion of extra-
the goal of reducing intestinal pH and thereby trapping hepatic shunts are cellophane bands and ameroid con-
ammonia within the gut, and by virtue of its action as an strictors. Cellophane bands promote occlusion by
osmotic cathartic, hastening intestinal transit time and stimulating a foreign body reaction and fibrosis between
reducing the time available for absorption of ammonia. the band and the shunt wall. Ameroid constrictors pro-
In patients that are actively encephalopathic and unable duce some mechanical occlusion as the ameroid clay
to tolerate oral medication, lactulose may be adminis- takes up fluid, but also cause local inflammation with
tered rectally. fibrosis and thrombosis of the shunt vessel. More recent
Antibiotics may also be prescribed, with a view to reports have described the use of a variety of other clear
reducing the intestinal bacterial population and thus films for shunt occlusion in dogs and cats, including
reducing ammonia production. Further details about polypropylene and polyethylene. These seem to be as
medical management of the patient with liver disease effective as cellophane, probably due to the chemicals
can be found in Chapter 65. incorporated during the manufacturing process.