ABSTRACT: A portosystemic shunt (PSS) is an abnormal vascular communication between the systemic and portal circulations, with blood bypassing the liver, and it is a common abnormality of the hepatobiliary system in the dog and cat. The aim of this article is to define different types of PSS, to discuss the presentation of patients and the diagnostics involved and outline nursing care involved with congenital PSS patients.

Types of portosystemic shunt (PSS)

A shunt may be:

intrahepatic – believed to be an anomalous vessel or persistence of the foetal ductus venosus post parturition extrahepatic – the shunt arises from the portal vein, gastric veins or splenic veins with connection to either the caudal vena cava, azygous vein or another systemic vessel congenital – commonly seen in pure- breed dogs, including the Pug, Yorkshire terrier and Labrador retriever. In the cat, a congenital PSS is more commonly seen in mixed breeds acquired – secondary to portal hypertension, usually resulting from chronic, diffuse, intrahepatic disease, for example, cirrhosis. Acquired PSSs are rarely seen in the cat and are more commonly documented in older dogs.


Neurological abnormalities that are common presenting signs in the PSS patient include: tremors circling head-pressing lack of awareness seizures.

These signs are the consequence of shunting of unfiltered blood directly into the systemic circulation, resulting in hepatic encephalopathy (HE). HE is a consequence of the cerebral cortex being exposed to toxins in the blood that have not been removed by the liver.

Additional clinical signs can include lack of weight gain, poor appetite, polyuria/polydipsia (PUPD), vomiting and diarrhoea. The presenting pet may be considered the ‘runt’ of the litter. On clinical examination, abdominal palpation may reveal renomegaly – this is an effect of the circulatory changes and usually does not represent renal disease.


The majority of PSSs are diagnosed when the animal is less than one year old; but, if clinical signs are mild, they may go unnoticed and diagnosis may not be achieved until the animal is middle aged. Although it is the veterinary surgeon’s role to make a diagnosis of PSS, it is useful for the veterinary nurse (VN) to be aware of the tests with which they might be required to assist.

Diagnostic tests

The most useful diagnostic test to confirm a PSS is ultrasonography – to visualise the shunting vessel and measure portal flow to monitor for hypertension. Ultrasonography also allows measurement of liver size and assessment of texture.

Other tests that can be indicative – but not conclusive – of PSS include measurement of bile acids, biochemistry and ammonia levels:

• haematology – occasional anaemia, usually caused by changed serum ion concentrations; and possible alterations in leucocyte numbers resulting from decreased bacterial clearance

•  ammonia – reduced metabolism of ammonia results in increase in blood levels

•  pre- and postprandial bile acids – bile acids are normally synthesised by the liver and stored in the gall bladder, being released when the animal has eaten to assist fat digestion and absorption, reabsorbed in the ileum, and returned to portal circulation. In the PSS patient, when there is a shunting connection between the systemic and portal circulations, levels in the circulating blood are increased.

It is important to remember that increased levels of ammonia and bile acids only indicate liver dysfunction and are not specific to PSS.

Medical management and nursing care

Treatment of a PSS typically involves surgical intervention to ligate the anomalous vessel, and this will be discussed later. Prior to surgery being undertaken, the PSS case is managed medically for three to four weeks to ensure that signs of HE are fully resolved.

Pre-operative care

The pre-operative stage often involves a home-care plan being established with the owner. A prescription diet with controlled levels of protein might be advised. Alternatively, a home-cooked diet consisting of proteins of high biological value can be fed.

Lactulose is prescribed to reduce colonic pH, trap ammonium ions and inhibit protein and amino acid metabolism to increase nitrogen excretion via faeces.

Oral antibiotics are given to reduce numbers of colonic bacteria. The patient is regularly re-evaluated to ensure they are stable and any signs of HE are controlled.


When a patient is hospitalised prior to surgery, it is the VN s responsibility to administer the medications and to ensure it is receiving the correct diet. The VN is also required to monitor the patient for signs of HE and inform the veterinary surgeon if a problem arises.

During hospitalisation, intravenous fluid therapy (IVFT) may be indicated – for example, if the patient has increased losses upsetting the fluid balance in the body. The VNs role usually involves placement of the intravenous catheter, calculation of the required fluid rate (Table 1) and setting up the fluids decided on by the veterinary surgeon.

If the patient develops signs of HE, a lactulose retention enema may be prescribed. This route is sometimes chosen because the pH of the colon and levels of ammonia are decreased quicker than by oral administration.

Basic nursing is important to ensure holistic nursing care. This includes regular checking of beds for urination and regular replenishment of water, especially resulting from the PUPD, and also regular walking outside for toileting purposes.

If the patient presents with anorexia, tempting with the prescribed diet may be required and regular bathing and grooming is essential when lactulose has been prescribed. Any patient receiving IVFT requires regular catheter checks, involving undressing and redressing the catheter site, checking for signs of phlebitis or extravasation and flushing to ensure patency of the catheter.

Surgical options

There are a number of options for surgical intervention in the PSS patient, and, owing to the decreased incidence of post-surgical portal hypertension, techniques allowing gradual closure of a shunt are preferred. These include the following procedures.

Suture ligation

Suture ligation involves ligation of the anomalous vessel, either partially or completely, using silk suture material. Silk suture material is frequently used because of knot security and ease of handling.

The portal and systemic pressures
are monitored during the procedure to detect changes in response to the ligature. If full ligation causes excessive portal hypertension, then the vessel can be partially ligated. However, there is then a subsequent risk of recurrence of clinical signs.

Cellophane bands

The cellophane band technique involves placement of a cellophane band around the anomalous vessel. This initiates an inflammatory response, inciting a chronic foreign body type reaction.

Ameroid constrictors

Ameroid constrictors are implants used for gradual constriction. They consist of an inner ring of casein contained within a stainless steel ring. Casein is a hygroscopic substance that slowly swells as it absorbs bodily fluids. The steel casing ensures expansion inwards, occluding the vessel. The implant also results in a fibrous tissue reaction, completing vessel closure. 

Coil embolisation

Coil embolisation is a minimally invasive procedure involving intravascular coils that are used in occlusion of both extra- hepatic and intra-hepatic shunts. Intra- caval expandable stents are also placed, to prevent the coils moving.

Postoperative care of the PSS patient

Portal hypertension

There are a few risks as a result of any of the surgical options discussed.

Acute portal hypertension can occur as a result of the shunt closure. This is increased pressure in the portal vein, which carries blood from the spleen and intestines, resulting from the surgical obstruction. It is a potentially serious complication that requires emergency intervention to remove the surgical obstruction.

The VN monitors for signs of abdominal distension and pain, extreme systemic hypotension and hypovolaemic shock.

Other post-surgical considerations include pain management. The veterinary surgeon may utilise a pain-scoring system for the VN to implement, and provide instructions on the analgesia to be administered. IVFT is usually continued during recovery and the VN must continue with catheter checks.

Antibiotics and lactulose are also continued postoperatively under the instruction of the veterinary surgeon. The patient may be hypothermic after surgery and the VN must monitor and consider warming techniques, including heat pads. Other general surgical aftercare factors, including wound management and introduction of nutrition, should be considered and the VN must have a good knowledge of basic nursing techniques.

Case example

A three-month-old Cocker spaniel was presented at the practice following an episode of disorientation and suspected seizure activity. On clinical examination he was bright and in good body condition and physical examination was unremarkable. He was admitted for further diagnostic tests.

Blood was collected for testing:

• haematology revealed a mild anaemia

•  biochemistry revealed elevated alanine aminotransferase (ALT) at 292/l (normal reference for the analyser 13-88/l) 

•  pre- and postprandial bile acids were raised.

Abdominal ultrasonography (AUS) was performed revealing an extrahepatic PSS communicating with either the azygous vein or vena cava.

The patient was discharged with a home-care plan consisting of administration of clavulanate-potentiated amoxicillin (Synulox, Pfizer Animal Health) and lactulose per os and feeding of suitable diet for a period of four weeks prior to surgery. Regular examinations were carried out during this time to monitor for signs of HE and the owners were advised to monitor for neurological signs, which were described to them.

After four weeks, the patient was admitted for surgery. The technique chosen for this particular patient was cellophane banding and the procedure was performed without complication. Postoperative monitoring was carried out by a VN, the systemic blood pressure was observed and the patient was assessed for abdominal distension and pain.

A pain scoring system was established by the veterinary surgeon in the days following surgery and antibiotics and lactulose were continued. The post-surgical period was uneventful and the patient was discharged after five days.

Currently the patient is still receiving antibiotics and lactulose, at a reduced dose, and is due for re-assessment of blood ammonia levels and bile acids, along with a repeat AUS to check the PSS is closed and to measure portal vein pressure.


In conclusion, the PSS patient can be a challenging case both pre- and postoperatively. Although there are specific factors that can result from the procedure to correct the condition, it is essential the VN does not forget to fulfil the basic nursing requirements that promote holistic nursing care. 


Laura Crump RVN MBVNA

Laura joined Dick White Referrals shortly after qualifying in 2010 and works in the internal medicine department. She enjoys all types of medical nursing but has a particular interest in oncology and emergency medicine. She is currently studying to gain her RCVS DipAVN.

To cite this article use either

DOI: 10.1111/j.2045-0648.2012.00225.x or Veterinary Nursing Journal Vol 27 pp 370-372

Useful reading

NELSON. R. M and COUTO. C. G [Eds] Small Animal Internal Medicine [4th Edition], Mosby Elsevier. Missouri. 2008.

HOTSTON MOORE. A. and RUDD. S. [Eds] BSAVA Manual of Canine and Feline Advanced Veterinary Nursing (2nd Edition]. British Small Animal Veterinary Association. Gloucester. 2007.


• VOL 27 • October 2012 • Veterinary Nursing Journal