Uniform intrahepatic portal ammonia distribution in cirrhosis.

Lower rates of hepatic encephalopathy (HE) following left-sided transjugular intrahepatic portosystemic shunt (TIPS) placement have been hypothesized to stem from a distinct ammonia distribution within the portal venous system. This prospective study investigated ammonia concentrations at five portal and splanchnic venous sites in 50 fasting cirrhotic patients (20 female [40%]; mean age: 60.4 years) prior to TIPS implantation for ascites (33/50, 66%) or variceal bleeding (17/50, 34%). While ammonia levels were significantly higher in the superior mesenteric vein (mean: 143 µg/dl) compared to the splenic vein (mean: 66 µg/dl; p < 0.001), mean ammonia concentrations in the right (104 µg/dl) and left (107 µg/dl) portal vein branches were found to be equivalent (p = 0.008 for equivalence). No systematic differences between right and left portal vein ammonia were observed. These findings suggest that in fasting cirrhotic patients, local ammonia levels in the main portal vein branches do not differ significantly. Therefore, other factors likely contribute to any observed differences in HE rates related to TIPS placement site, warranting further investigation into alternative mechanisms.