Predisposed Breeds:

• Extrahepatic PSS: Yorkshire Terrier, Maltese, Bichon Frise, Miniature Schnauzer, Pug
• Intrahepatic PSS: Irish Wolfhound, Golden Retriever, Labrador Retriever, Samoyed

Clinical Signs:

• Hepatic encephalopathy: behavioral changes, circling, head-pressing, ataxia, seizures, coma
• Failure to thrive: poor body condition, stunted growth in young animals
• Post-prandial deterioration: signs worsen 2–6 hours after protein meals
• Ptyalism (hypersalivation) — particularly common in cats with PSS
• Polyuria/polydipsia
• Urinary signs: uroliths (ammonium biurate — "thorn-apple" crystals on urine sediment), dysuria, hematuria

Diagnostic Tests:

• 12-hour fasted SBA and 2-hour post-prandial SBA
• Post-prandial SBA >25 µmol/L is highly suggestive of portovascular abnormality
• Post-prandial SBA >100 µmol/L strongly suggests PSS
• Sensitivity for PSS: ~90–95%; specificity varies with cut-off

Blood Ammonia:

• Fasting ammonia >100 µmol/L (or above lab reference range) supports hepatic encephalopathy
• Pre/post-exercise ammonia tolerance test: doubles accuracy but requires careful patient selection
• Ammonia is unstable; must be analyzed within 30 min or stored on ice

Routine Blood Work:

• Microcytic anemia (iron redistribution due to hepatic dysfunction)
• Low BUN (decreased urea synthesis)
• Hypoalbuminemia, hypoglycemia (severe cases)
• Mildly elevated ALT/ALP (variable; often normal)
• Prolonged coagulation times (factors II, VII, IX, X synthesized in liver)

Imaging:

• Abdominal ultrasound: identify shunt vessel location; microhepatica (small liver); identifies intrahepatic vs extrahepatic
• CT angiography (gold standard imaging): precisely maps shunt anatomy, diameter, and location — essential for surgical planning
• Scintigraphy (trans-splenic portal scintigraphy): quantifies shunt fraction; minimally invasive but less anatomic detail

Urinalysis:

• Ammonium biurate ("thorn-apple") crystals on sediment — highly suggestive of PSS or hepatic dysfunction
• May have proteinuria, hematuria if urolith present

Dietary Management — Foundation of Medical Therapy:

• Moderately protein-restricted, highly digestible diet
• Target: 14–17% protein DM for dogs (not severely restricted — avoid muscle wasting and impaired urea cycle)
• Preferred protein sources: dairy (casein), soy, or egg (lower ammoniagenic potential than meat)
• High-carbohydrate, highly fermentable fiber content promotes enteric ammonia trapping
• Feed multiple small meals (3–4x daily) to reduce post-prandial ammonia spikes
• Prescription hepatic diets (Royal Canin Hepatic, Hill's l/d) are appropriate

Lactulose — Enteric Ammonia Reduction:

• Mechanism: osmotic cathartic + acidification of colon (NH3 → NH4+ trapped in stool)
• Dose: 0.25–0.5 mL/kg PO q8–12h; titrate to 2–3 soft stools per day
• Use syrup formulation; avoid propylene glycol-containing products in cats
• Can be given as retention enema (diluted 3:1 with warm water) in encephalopathic animals

Antibiotics — Reduce Urease-Producing Gut Flora:

• Neomycin: 20 mg/kg PO q12h — historically used; poor systemic absorption; GI side effects
• Metronidazole: 7.5–15 mg/kg PO q12h — preferred; also has anti-inflammatory GI effects; use with caution in HE (can cause neurotoxicity at high doses)
• Rifaximin: 2.5–5 mg/kg PO q12h — minimal systemic absorption; emerging evidence in small animals
• Course: 4–8 weeks; reassess; antibiotics are adjunctive to dietary management

Seizure Management:

• Phenobarbital is AVOIDED in PSS — hepatic metabolism impaired, accumulation risk, direct hepatotoxicity
• Levetiracetam (Keppra) is preferred: 20 mg/kg PO/IV q8h — not hepatically metabolized, renal excretion
• Potassium bromide — adjunctive if needed; slow onset; use with care given renal clearance
• For acute seizure clusters: midazolam 0.1–0.2 mg/kg IN/IV is safest benzodiazepine

IV Fluids for Encephalopathic Episodes:

• 0.9% NaCl or Plasma-Lyte without lactate (lactate must be metabolized by liver)
• Supplement potassium (hypokalemia worsens encephalopathy)
• Dextrose supplementation if hypoglycemic (2.5–5% CRI)
• Avoid lactated Ringer's solution in severe hepatic failure

1. Ameroid Constrictor (most common for extrahepatic PSS):

• Casein ring that gradually swells over 4–8 weeks as it absorbs fluid, progressively occluding the shunt vessel
• Gradual occlusion reduces risk of acute portal hypertension
• Complete occlusion confirmed at 4–8 weeks; partial occlusion in ~15–20% of cases

2. Cellophane Band Attenuation:

• Cellophane band placed around the shunt vessel; fibrous reaction gradually occludes over weeks
• Attrition rate similar to ameroid

3. Intravascular Coil Embolization (intrahepatic PSS):

• Interventional radiologic technique; coils placed within the shunt vessel via transjugular or transabdominal approach
• Preferred for intrahepatic PSS (right-divisional or left-divisional)
• Requires specialist center with interventional radiology capability

4. Acute Ligation:

• Sudden occlusion carries high risk of fatal portal hypertension
• Only used in dogs with good portal tolerance demonstrated intraoperatively (portal pressure <20 cmH2O after test occlusion)

Post-Surgical Management:

• Continue medical management (diet, lactulose) for 4–8 weeks post-surgery until adequate occlusion confirmed
• Post-op SBA at 4 and 12 weeks — if still markedly elevated, assess for residual shunting
• Monitor for: acute portal hypertension (abdominal pain, hemorrhagic diarrhea), seizures (2–7 days post-op), hypoglycemia
• Levetiracetam 20 mg/kg PO q8h for first 2 weeks post-surgery to reduce seizure risk

When Surgery Is Contraindicated:

• Acquired PSS from portal hypertension (hepatic cirrhosis): multiple small vessels — surgical closure worsens portal hypertension
• Severe hepatic dysfunction (albumin <1.5 g/dL, prolonged PT >2x normal): high anesthetic/surgical risk
• These patients are managed long-term medically with diet, lactulose, and antibiotics