The Influence of the Surgical Outcome on Blood and Cerebrospinal Ammonia Levels in Dogs with Congenital Extrahepatic Portosystemic Shunts

Objective
To compare ammonia in arterial blood (A), venous blood (V) and cerebrospinal fluid (CSF) in dogs with and without portosystemic shunts (PSS).

Study Design
Prospective clinical trial.

Animals
6 dogs with congenital PSS and 15 control dogs without PSS (7 clinically healthy, 8 with seizures).

Methods
A transsplenic portal scintigraphy (TSPS) was performed to confirm the diagnosis of PSS and to calculate the shunt fraction (SF). The cellophane banding technique was used with an initial shunt attenuation of 50% at the time of surgery. Three months postoperatively, TSPS was repeated. In the PSS dogs, ammonia was measured at the time of diagnosis (T0: A, V), on the day of surgery (T1: A, V, CSF) and at 1 (T2: V) and 3 months (T3: A, V, CSF) after surgery. In the control dogs, samples for ammonia measurement were collected at one occasion (healthy dogs: A, V, CSF and seizure dogs: V, CSF). For statistical analysis, nonparametric tests were used at a significance level of 0.05.

Results
At T0 and T1, blood ammonia was consistently higher in PSS dogs than in the healthy (P<0.01) and seizure dogs (P<0.01). At T2 and T3, blood ammonia was normal in 6/6 and 5/6 dogs, respectively. The original shunting vessel was closed in 5/6 dogs, but 2 had evidence of acquired shunting (blood ammonia was normal in one). The original shunt was patent in 1 dog (blood ammonia was normal). A correlation of 94.5% was found between A and V ammonia in the PSS dogs at any time point (P<0.01). CSF ammonia at T1 was significantly higher in the PSS dogs compared to healthy (P<0.05) and seizure dogs (P<0.05). A significant positive correlation was demonstrated between A or V ammonia concentration and the CSF ammonia concentration (P<0.01) in PSS patients. The CSF ammonia concentration at T3 was lower compared to T1 in all PSS dogs with exception of the dog with the persistent shunt.  [...]