EFFECT OF INTRAHEPATIC PORTAL-SYSTEMIC SHUNTING ON HEPATIC AMMONIA EXTRACTION IN PATIENTS WITH CIRRHOSIS

Increased plasma ammonia levels in patients with advanced cirrhosis ha ve been attributed to reduced conversion of enteric ammonia to urea by the diseased liver and to entry of enteric ammonia into systemic circ ulation by way of portal-systemic shunts. Because single-pass extracti on is high for portal venous ammonia, reduction of portal blood supply to hepatocytes may have detrimental effects on the hepatic extraction of ammonia. To assess how the development of intrahepatic portal-syst emic shunts alters hepatic ammonia metabolism, we determined portal an d hepatic venous ammonia levels along with measurements of intrahepati c portal-systemic shunts using Tc-99m-macroaggregated albumin in 46 pa tients with portal hypertension. Hepatic venous ammonia levels in the groups of patients with idiopathic portal hypertension, Child class A cirrhosis and Child class B or C cirrhosis were 36 +/- 17, 75 +/- 26 a nd 93 +/- 52 mu g/dl, respectively, in increasing order, and portal ve nous ammonia extraction rates as calculated with the equation (portal venous ammonia - hepatic venous ammonia)/portal venous ammonia x 100% were decreased in the same order (77% +/- 14%, 50% +/- 21%, 40% +/- 25 %, respectively). Furthermore, we noted a significant negative correla tion between the intrahepatic shunt indexes as calculated by counts pe r minute in lungs/counts per minute in lungs and liver x 100% and the ammonia extraction rates. It was noteworthy that among Child class C p atients, the ammonia extraction rates were significantly lower in pati ents with high intrahepatic shunt indexes than in those with low shunt indexes. These results demonstrate a significant direct relationship between hepatic ammonia extraction rates and intrahepatic shunting in cirrhosis.