Ammonia concentrations in arterial blood, venous blood, and cerebrospinal fluid of dogs with and without congenital extrahepatic portosystemic shunts

OBJECTIVE To compare ammonia concentrations in arterial blood, venous blood, and CSF samples of dogs with and without extrahepatic portosystemic shunts (EHPSS). ANIMALS 19 dogs with congenital EHPSS and 6 healthy control dogs. PROCEDURES All dogs underwent a physical examination and then were anesthetized for transsplenic portal scintigraphy to confirm the presence or absence of EHPSS. While dogs were anesthetized, arterial and venous blood samples and a CSF sample were simultaneously collected for determination of ammonia concentration, which was measured by use of a portable blood ammonia analyzer (device A) and a nonportable biochemical analyzer (device B). Results were compared between dogs with EHPSS and control dogs. RESULTS Arterial, venous, and CSF ammonia concentrations for dogs with EHPSS were significantly greater than those for control dogs. For dogs with EHPSS, ammonia concentrations in both arterial and venous blood samples were markedly increased from the reference range. There was a strong positive correlation between arterial and venous ammonia concentrations and between blood (arterial or venous) and CSF ammonia concentrations. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that blood and CSF ammonia concentrations in dogs with EHPSS were greater than those for healthy dogs and were strongly and positively correlated, albeit in a nonlinear manner. This suggested that the permeability of the blood-brain barrier to ammonia may be abnormally increased in dogs with EHPSS, but further investigation of the relationship between blood or CSF ammonia concentration and clinical signs of hepatic encephalopathy or the surgical outcome for dogs with EHPSS is warranted.