Читать книгу Emergency Management of the Hi-Tech Patient in Acute and Critical Care - Группа авторов - Страница 70

Creation of a TIPS introduces a stent across hepatic tissue from the hepatic vein to the portal vein. Hepatic tissue reacts to this placement and begins to create a pseudo‐intima around and into the shunt. Increase in tissue into an uncoated stent begins to narrow the lumen of the stent and decrease the portosystemic blood flow, making the stent less effective. This then allows portal hypertension to recur, and patients have an increased risk in esophageal variceal bleeding and redevelopment of ascites.

Doppler ultrasonography is used as the initial screening method for shunt stenosis. Two main parameters are used for shunt patency. First, the velocity of flow within the TIPS is measured in multiple locations across the shunt. Single velocity measurement has a lower sensitivity and specificity than multiple measurements, with decrease in shunt velocity between 40 and 60 cm/s of significant elevated velocity over 200 cm/s identifying local stenosis. Main portal vein velocity is the second parameter. Stenotic shunts demonstrate lower main portal velocity and a change in the direction of flow toward the liver instead of normally away from the liver in a functioning stent. CT angiography can also be used in the evaluation of shunt stenosis; however, the gold standard of diagnosis of shunt stenosis is angiography. Stenotic shunts can be dilated during angiography and the placement of an additional stent ensures unobstructed flow of the TIPS.