Hepatic Hemodynamic (HVPG)
Normal portal pressure is generally defined between 5 and 10 mm Hg. However, once the portal pressure rises to 12 mm Hg or greater, complications can arise, such as varices and ascites. Many conditions are associated with portal hypertension, of which cirrhosis is the most common cause.
The portal vein drains blood from the small and large intestines, stomach, spleen, pancreas, and gallbladder. The portal trunk divides into 2 lobar veins. The right branch drains the cystic vein, and the left branch receives the umbilical and paraumbilical veins that enlarge to form umbilical varices in portal hypertension.
Hemodynamic Measurement of Portal Pressure
Direct portal measurements usually are not performed due to the invasive nature, the risk of complications, and the interference of anesthetic agents on portal hemodynamics. The most commonly used method is measurement of the hepatic venous pressure gradient (HVPG), which is an indirect measurement that closely approximates portal venous pressure. A fluid-filled balloon catheter is introduced into the femoral or internal jugular vein and advanced under fluoroscopy into a branch of the hepatic vein. Free hepatic venous pressure (FHVP) then is measured. The balloon is inflated until it is wedged inside the hepatic vein, occluding it completely, thus equalizing the pressure throughout the static column of blood. The occluded hepatic venous pressure (ie, wedged hepatic venous pressure) minus the unoccluded, or free, portal venous pressure (ie, FHVP) is the HVPG.