Peritoneovenous Shunt

Indications

PVS is effective in the drainage of the peritoneal fluid in patients with chronic refractory ascites.[3] The most common indication for insertion of PVS is medically intractable ascites secondary to chronic liver diseases. Conditions that result in chronic ascites that is unresponsive to medical therapy are best treated with PVS. These include acute and chronic liver diseases like cirrhosis, malignant ascites due to malignant tumors of the breast, ovary, or colon, chylous ascites, congestive heart failure, chronic kidney disease (CKD), and portal vein thrombosis.[4][5][4] PVS is indicated under the following conditions:

• Malignant or cirrhotic ascites unresponsive to medical treatment and large volume paracentesis
• Chylous ascites 
• The patient is unresponsive to diuretics. 
• The patient is not a candidate for liver transplantation.
• The patient is not a candidate for serial therapeutic paracentesis due to extensive abdominal surgical scars.
• The patient has a life expectancy of more than three months.
• The patient has no contraindication to PVS.
• Non-availability of physicians to perform serial therapeutic paracentesis

Contraindications

Generally, PVS is contraindicated in patients with end-stage renal failure on dialysis, septicemia, uncorrectable coagulopathy, morbidly obese patients, and patients with septation of the peritoneal cavity due to previous infection or surgery.[6] Denver shunts placement is absolutely contraindicated in bloody ascites, renal failure, history of varicose vein bleeding, grade 3/4 esophageal varices, congestive heart failure, respiratory failure with pulmonary edema, liver failure (total bilirubin >2.0 mg/dL), coagulation disorders (platelet count <50 ×10/ INR>2.0), history of peritonitis or spontaneous bacterial peritonitis, poor performance status, hypoalbuminemia (serum albumin<2.5g/dL) and evidence of nonsterile ascites. It is relatively contraindications in patients with compensated congestive heart failure, loculated ascites, peritoneal disease, massive pleural effusion, non-bleeding varices, portal hypertension, and simultaneous gastrointestinal surgery.

Equipment

Over time, there have been various modifications to the original design of the shunts for Peritoneovenous shunting, notably the Hyde shunt, Laveen shunt, and most popularly, the Denver shunt. The shunt comprises of two Silastic tubes connected via a compressible pump. The shunt catheter is available in two sizes, 11.5 French (F) and 15.5F. The compressible pump is either single-valved or double-valved, which opens upon a pressure difference of more than 3 cm of water across the two ends of the shunt.

The flow rate depends upon the size of the shunt and compression pump valve. Compared to the double-valved shunt, the single-valve shunt has a higher flow rate for both the shunt catheter sizes. The 15.5F double-valve shunt, however, is most widely used as it is least likely to get occluded or cause reflux.[7]

Personnel

A team comprising of an Interventional radiologist, nurse, and radiology technician performs the procedure. All the team members must have specialized and extensive training in the procedure.

Preparation

Before the procedure, the laboratory values obtained are as follows: complete blood count, coagulation profile, blood urea nitrogen(BUN), creatinine, serum albumin, and liver function tests(LFTs). The ascitic fluid is obtained by paracentesis and examined for total polymorph count, protein, and albumin and culture. The serum-ascitic fluid albumin gradient (SAAG) is calculated to establish the cause of ascites. SAAG >1.1g/dl excludes cancer as the cause of ascites. Broad-spectrum prophylactic antibiotics are administered to the patient intravenously before the procedure and for a week after the procedure to prevent the risk of infection. The patient requires moderate sedation for the procedure, mostly in an outpatient setting.

Technique or Treatment

The most commonly used PVS is the Denver shunt, which a modified version of the original design.[8] After the patient is prepped and draped, an all-purpose drainage (APD) catheter is inserted at the upper abdominal region to drain the ascitic fluid. It is then replaced with the peritoneal end of the shunt after priming it with warmed saline. It is inserted between the right hepatic lobe and the ribs. The second incision is made on the lower rib cage for the placement of the compressible pump. It must be placed against a firm, stable rib for effective compression. The third incision is made at the venous access site. Using a long metallic tunneler, the shunt is traversed towards the neck, ideally subcutaneously; however, it can also be placed percutaneously.[3] 

The venous end of the shunt is inserted into the superior vena cava via the internal jugular veins or the subclavian veins under fluoroscopic guidance until the catheter tip ends in the proximal right atrium. A one-way pressure-sensitive valve is attached to prevent the backflow of blood from the venous end of the shunt.

Complications

Complications from PVS are common and include peritoneal infection, variceal bleeding, superior vena cava thrombosis, pulmonary edema, disseminated intravascular coagulation (DIC), scar tissue formation, shunt fracture, occlusion, displacement or leakage, pneumothorax, and pneumoperitoneum. The most common complication of PVS is shunt occlusion, with only 18.6% of shunts remaining patent at two years, according to a study.[3] 

About 9% of the patients report with disseminated intravascular coagulation (DIC) after shunt insertion.[9] This condition may be due to the presence of activating factors like tissue factor (TF) that initiate thrombogenesis.[10] Thrombosis of the shunt is a rare occurrence and mainly involves the tip of the venous end of the shunt.[11] Staphylococcal and gram-negative organisms can result in perioperative infections, which may progress to bacterial peritonitis or sepsis.

Clinical Significance

Regardless of the complications, PVS insertion successfully treats refractory ascites in most patients with chronic liver disease, leading to a significant improvement in the quality of life.[12] PVS is a simple procedure as the placement of the entire shunt is subcutaneous, which allows the patient to be able to perform activities that require submersion in water like swimming and bathing, unlike indwelling tunneled drainage catheters.[13] As the fluid returns from the peritoneal cavity into the circulation, there is no loss of nutrients which benefits by reducing the risk of malnutrition in chronically ill patients.

Enhancing Healthcare Team Outcomes

The most common complication of PVS is shunt blockage. All patients should be instructed to pump the compressible pump of the PVS several times a day in the supine position for maximal drainage. The interventional radiologist should counsel the patient and/or the caregiver regarding clear instructions on how and when to compress the shunt pump before discharging the patient.

Abstinence from alcohol consumption can lead to shunt blockage due to a reduced flow rate, and these patients require careful monitoring. Less common complications, notably coagulopathy and edema, can be prevented by complete drainage of ascitic fluid before shunt placement. Broad-spectrum prophylactic antibiotics help to prevent peri- or post-operative infections; however, complicated infections require shunt removal. Percutaneous PVS has several advantages over subcutaneous PVS as the former is minimally invasive, faster, less painful, cheaper, and doesn’t require sedation.[14] 

The interventional radiologist, hepatologist, and liver transplant surgeon should work closely to explore the best treatment plan for each patient.