Definition

Portal pressure >13 cm H₂O or 10 mm Hg

Pathophysiology

• Causes-increased portal blood flow (arterialized system); increased resistance to portal blood flow, or a combination of factors.
• Portal vein-lacks valves; blood follows a path of least resistance.
• Increased Portal Flow-arterialization of portal circulation occurs in AV malformation or subsequent to increased hepatic resistance; causing retrograde blood flow into the valveless splanchnic portal circulation.
• Hepatofugal-portal splanchnic circulation away from the liver.

Systems Affected

• Hepatobiliary disorders-obstructed blood flow in any zone or diffusely across sinusoids causes intrahepatic PH, splanchnic PH, ± passive splenic congestion (splenomegaly).
• Posthepatic disorders-hepatic passive congestion, hepatomegaly, and variable PH; APSS usually absent because of a lack of pressure differential between splanchnic portal vein and vena cava.
• Prehepatic disorders-cause splanchnic PH, splenic congestion (splenomegaly) and APSS; portal venous thrombi, stenosis, stricture, entrapment within porta hepatis (e.g., pancreatitis, neoplasia), mass compression (pancreatic inflammation; neoplasia).
• Nervous-HE due to APSS.
• Cardiovascular-APSS and ascites may develop with vena caval/hepatic vein obstruction (at the level of the diaphragm), but not with congestive heart failure or pericardial tamponade as these dually increase hydrostatic pressure in both hepatic and vena caval systems.
• Portal thrombi-caused by gastrointestinal inflammation/necrosis and splanchnic vasculitis, neoplasia, DIC, loss of anticoagulants, accelerated thrombosis.
• Gastrointestinal-splanchnic hypertension can provoke enteric edema, increased gut wall permeability provoking transmural bacterial translocation (endotoxemia, bacteremia), hypertensive enteric vasculopathy (enteric bleeding, ulceration), diapedesis blood loss, and protein malassimilation.

Genetics

• Vascular malformations causing portal atresia (intrahepatic, prehepatic) are congenital and represent a severe phenotype of polygenic portal venous malformations in small-breed dogs (see Portosystemic Vascular Anomaly, Congenital).
• Ductal plate malformation (DPM): congenital hepatic fibrosis (CHF) phenotype causes APSS; these represent dysfunction of primary cilia; occur in numerous dog breeds and Persian related cats; increased frequency in Boxers; genetic cause and heritability not specifically studied in dogs; feline polycystin-1 precursor mutation has 15% occurrence.
• Non-cirrhotic PH: adult-onset diminution of tertiary portal branches, affects individual dogs of many breeds, described in Doberman pinschers rare).
• Acquired sinusoidal PH due to necroinflammatory liver injury-immune-mediated chronic hepatitis (anecdotal in some breeds).
• Copper associated hepatopathy-Bedlington terrier COMMD1 mutation, predisposition for copper associated hepatopathy in Labrador retrievers, Dalmatian, Doberman pinscher, and numerous other dogs may reflect pharmacogenetic breed differences in copper transporters (see Copper Associated Hepatopathy).

Signalment

Signs

Causes

Risk Factors

Depend on underlying cause

Differential Diagnosis

• Physicochemical analysis of abdominal effusion-helps narrow diagnoses
• Pure transudate-hypoalbuminemia secondary to PLE, PLN, liver failure
• Modified transudate with normal or low albumin-PLE, PLN, liver failure (chronic effusion), neoplasia, splanchnic TE, liver (visceral) entrapment in diaphragmatic hernia
• Modified transudate with large liver and jugular distention-cardiac or pericardial abnormalities; heartworm; right atrial tumor
• Modified transudate with large liver without jugular distention, muffled heart, or pulmonary edema-kinked vena cava; Budd-Chiari-like or sinusoidal occlusion syndrome
• HE-liver fibrosis; cirrhosis; CHF; hepatic AV malformation; any cause of APSS
• Jaundice-chronic hepatitis, cholangitis; EHBDO; infiltrative hepatic neoplasm
• Bloody diarrhea, abdominal pain, ileus, signs of endotoxemia-acute splanchnic portal TE

CBC/Biochemistry/Urinalysis

• CBC-schistocytes with TE; RBC microcytosis with PSVA or APSS; icteric plasma with liver disease or microangiopathic shearing anemia (also show schistocytes).
• Biochemistry-liver disease associated with variable liver enzymes, low BUN, creatinine, cholesterol, and/or glucose concentrations, hyperbilirubinemia, and coagulation abnormalities; Posthepatic disorders associated with high liver enzymes, ± azotemia, and normal plasma color.
• Urinalysis-ammonium biurate crystalluria with APSS; may note granular casts with TE affecting renal perfusion; may note proteinuria with heartworm disease.

Other Laboratory Tests

• TSBA-variable fasting and high 2-h postprandial concentrations with APSS or hepatobiliary disease; shunting pattern (normal fasting and markedly high postprandial values) common.
• Blood ammonia-hyperammonemia with APSS or inferred by finding ammonium biurate crystalluria; ammonia tolerance testing and ammonia measurement less convenient and reliable compared to TSBA.
• Physicochemical characterization of abdominal effusion-high serum:effusion albumin ratio (>1.1) consistent with PH.

Imaging

Additional Diagnostics

• Electrocardiography and central venous pressure-with cardiac disease, cranial mediastinal obstructions.
• Liver biopsy-required for diagnosis of hepatobiliary disorders.
• Portal pressure-although may be measured during laparotomy is not recommended; unreliable in deducing underlying causes; PH blunted by APSS PH adequately confirmed with imaging studies and on gross inspection.

Appropriate Health Care

Inpatient-for severe HE, amelioration of tense ascites by therapeutic abdominocentesis, supportive care for acute TE.

Nursing Care

• Fluid therapy-with all causes, restrict sodium concentration (avoid 0.9% NaCl); high likelihood of total-body sodium loading. Avoid iatrogenic pulmonary edema during fluid therapy (caution: if hypoalbuminemia).
• Monitor body weight and condition, girth circumference, plasma proteins, and PCV-assess hydration status, volume of abdominal effusion, and IV fluid tolerance.
• Low oncotic pressure-may require plasma or colloid administration (plasma preferred for liver patient); Voluven or VetStarch (6%; 130 MW/0.4 molar substitution) 10–20 mL/kg/day IV CRI) may be necessary for acute adjustments; avoid Hetastarch as can reduce platelet function.
• Glucose supplementation-with hepatic dysfunction and hypoglycemia; 2.5–5.0% dextrose with half-strength polyionic fluids initially; titrate dextrose concentration to achieve euglycemia (avoid hyperglycemia).

Mobilization Of Ascites

• Abdominal effusion-sequentially assess: body weight, girth, and body condition score; initially exercise restrict (improves renal perfusion, sodium and water elimination); enforce dietary sodium restriction.
• Conventional diuretics: combine furosemide and spironolactone; furosemide (0.5–2 mg/kg PO q12–24h) and spironolactone (0.5–2 mg/kg PO q12h, use a single doubled dose for loading one time): dose titrations based on response q4 days; adjust using incremental 25–50% dose increase. Spironolactone: potassium sparing; less potent than furosemide. Furosemide: potassium wasting, diuresis induces RAAS response. Serum:effusion albumin ratio (>1.1) may predict response to diuretics.
• Vasopressin V₂ antagonists (aquaretics) may assist with management of diuretic resistant ascites. Tolvaptan successful in dogs with experimentally induced (rapid pacing) congestive heart failure. Human dose in cirrhosis is 7.5 mg/day; Tolvaptan is metabolized exclusively in the liver primarily by cytochrome P450; dose undetermined in dogs with liver disease.
• Telmisartin: angiotensin receptor blocker (ARB, nephro-protective in diabetes and renal injury in humans, also prevents effects of drug-induced hepatotoxicity and hepatic fibrosis) is an alternative diuretic worthy of consideration. ARBs selectively antagonize angiotensin-1 receptor bypassing intermediary activation steps within the RAAS cascade. Telmisartan administration PO in at 1.0 mg/kg/day significantly increased urine volume and sodium excretion in healthy dogs.
• Taper diuretic dose after initial positive response; individualize chronic treatment to response; diuretics may be used intermittently to mobilize recurring ascites
• Avoid dehydration as this can lead to HE.
• Avoid hypokalemia as this can provoke HE.
• If cardiac disease is the cause of ascites: treatment involves sodium restriction, enalapril, furosemide, newer diuretics described above. Diuretic-resistant ascites-large volume (therapeutic) abdominocentesis if ascites resistant to medical intervention or compromises food intake, ventilation, or sleep: requires aseptic technique, fluid removal over 45–90 minutes, concurrent polyionic fluid and/or colloids reduces risk for post-centesis hypotension and acute renal failure (ARF). Repeated large-volume fluid removal may result in: hypovolemia, hypoproteinemia, electrolyte depletion; iatrogenic infection; postcentesis hypovolemia/hypoperfusion syndrome and ARF (rapid redistribution of fluid into abdominal cavity). Use aseptic technique and concurrently provide polyionic fluids in moderation with colloids. General rule in humans: provide 4–8 g of albumin per L of ascites removed (consider colloids, discussed above).
• If ascites fails to mobilize, consider measuring urine sodium output vs. sodium intake (dietary) to determine whether intake requires restriction or diuretics upward titration. Urine output should be measured over a minimum of 12 hours.

Activity

Depends on cause, restrict activity if ascites

Diet

• Ascites-restrict dietary sodium <100 mg/100 kcal.
• If HE-restrict dietary protein (see Hepatic Encephalopathy); caution: only restrict protein if nitrogen intolerance suspected.

Client Education

Inform client that definitive diagnosis requires logical diagnostic strategies and no prediction for cure or chronic amelioration until definitive diagnosis is ascertained.

Surgical Considerations

• Ligation of APSS or vena caval banding strongly contraindicated.
• If acute symptomatic PH after surgical ligation of PSVA-ligature removal imperative (see Portosystemic Vascular Anomaly, Congenital).
• Embolectomy of thrombi not recommended; emboli may recanalize with supportive care; clot dissolution (streptokinase , TPA) complicated, expensive, requires ICU hospitalization and monitoring, and warrants a grave prognosis.
• LMW heparin (see Coagulopathy of Liver Disease).
• Correction of chronic diaphragmatic hernia-release of entrapped viscera may provoke perioperative/postoperative endotoxemia, hypotension, shock, ARF.
• Surgical correction and cure of cor triatriatum and kinked vena cava are possible.
• Pericardectomy-pericardial restriction or tamponade; thoracoscopic procedure least invasive, with lowest mortality and best outcome.
• Removal of tumor or fibrous adhesions causing hepatic vein occlusion may be difficult.
• Removal (lobectomy) or embolization (acrylamide) of hepatic AV malformation may not be curative as microscopic intrahepatic AV shunting usually continues PH and APSS.

Drug(s) Of Choice

Treatment of abdominal effusion-sodium restriction (see above, “Diet”); combined diuretic therapy (spironolactone and furosemide), consider tolvaptan or telmisartin (see above), use large-volume paracentesis sparingly.

Diuretics

(see above; mobilization of ascites)

Contraindications

N/A

Precautions

N/A

Possible Interactions

• Avoid drugs relying on first-pass hepatic extraction, biotransformation, or hepatic elimination; if not possible, adjust dosage based on available information.
• Reduce dose of highly protein-bound drugs if patient hypoalbuminemic.
• Avoid NSAIDs: these are metabolized the P450 cytochrome–rich centrilobular regions where toxic adducts may provoke cell injury augmented by hypoxia, poor perfusion, sinusoidal occlusion, copper accumulation; NSAIDs may provoke ARF, sodium retention, and enteric bleeding that may augment HE.

Alternative Drug(s)

N/A

Patient Monitoring

• Sequentially monitor body weight, condition, and abdominal girth.
• Sequentially assess hydration, electrolytes, acid-base, and blood pressure as necessary.
• Monitor: albumin and glucose-with liver disease or APSS.
• Monitor lung sounds, pulse oximetry, and ventilatory effort-in cardiovascular disorders.

Possible Complications

• Thrombosis
• Endotoxemia
• Hypotension
• Hepatic encephalopathy
• Acute renal failure

Expected Course and Prognosis

Depends on cause

Associated Conditions

• Chronic liver disease
• Numerous disorders may cause prehepatic or posthepatic portal hypertension.

Pregnancy/Fertility/Breeding

Affects uterine perfusion and likely leads to abortion or stillbirths.

See Also

• Ascites
• Cirrhosis and Fibrosis of the Liver
• Congestive Heart Failure, Right-Sided
• Hepatic Encephalopathy
• Pericarditis
• Portosystemic Shunt, Acquired
• Portosystemic Vascular Anomaly, Congenital

Abbreviations

• ARF = acute renal failure
• APSS = acquired portosystemic shunt(s)
• ARB = angiotensin receptor blocker
• AV = arteriovenous
• CRI = constant rate infusion
• EHBDO = extrahepatic bile duct obstruction
• HE = hepatic encephalopathy
• PH = portal hypertension
• PLE = protein-losing enteropathy
• PLN = protein-losing nephropathy
• PSS = portosystemic shunting
• PSVA = portosystemic venous anomaly
• TE = thromboembolism
• TPA = tissue plasminogen activator
• TSBA = total serum bile acids