Arterial and venous ammonia concentrations in the diagnosis of canine hepato-encephalopathy.

Fasting venous ammonia concentrations were measured in 105 dogs with liver disease. In 69 of these patients and in 38 normal dogs simultaneous arterial and venous ammonia concentrations were measured. In patients with liver disease ammonia values were significantly higher in arterial blood than in venous blood, therefore arterial measurements are preferable for clinical diagnosis. A significant positive correlation was demonstrated between arterial or venous concentrations and the degree of hepato-encephalopathy. In an individual patient, however, the fasting ammonia concentration is an unreliable indicator of the degree of encephalopathy. Elevated ammonia values confirm the diagnosis of hepato-encephalopathy, but normal levels do not exclude it. A strong correlation was found between the existence of encephalopathy and the presence of portosystemic collateral circulation.