# Perioperative assessment of electroencephalography in dogs with congenital portosystemic shunts

## TL;DR

This study explores how EEG can help identify dogs at risk of neurological issues after surgery for congenital portosystemic shunts.

## Contribution

The study introduces perioperative EEG as a potential biomarker for predicting neurological outcomes in dogs with congenital portosystemic shunts.

## Key findings

- Dogs with normal pre-attenuation EEG had favorable outcomes during hospitalization.
- Abnormal pre-attenuation EEG was associated with early-onset seizures and higher mortality.
- Covert encephalopathy detected via EEG was linked to elevated ammonia concentrations.

## Abstract

Biomarkers to identify dogs at risk of developing seizures after surgical attenuation of congenital portosystemic shunts (CPS) have not been defined.

To prospectively characterize perioperative electroencephalographic findings in dogs with CPS undergoing shunt attenuation, and to evaluate their association with outcomes after attenuation.

Twenty-eight client-owned dogs with CPS enrolled prospectively.

A prospective cohort of dogs presenting with no overt signs of encephalopathy underwent ambulatory electroencephalography (EEG) before and after CPS attenuation. Electroencephalography background activity and presence of epileptiform or encephalopathic features were assessed qualitatively. Quantitative analysis evaluated the mean dominant frequency and relative power of EEG frequency bands.

Dogs with a normal pre-attenuation EEG (n = 24) did not develop early-onset (<7 days) PAS; however, 8% (2/24) experienced late-onset seizures (>30 days post-attenuation). Four dogs had abnormal pre-attenuation EEG. Two of these dogs developed early-onset seizures and 3 dogs (75%) died before discharge due to worsening neurological signs (n = 2) or immediate postoperative complication (n = 1). Pre-attenuation covert encephalopathy defined by EEG showed a combination of epileptiform features (4/4), abnormal background rhythm (3/4), and a lack of graphoelements of sleep (2/4). Median ammonia concentration (range) was 102.5 μg/dL (34-401) in non-encephalopathic dogs and 145.5 μg/dL (56-275) in dogs with covert encephalopathy.

Electroencephalography could provide useful diagnostic biomarkers to identify dogs at high risk of developing neurological complications after attenuation of CPS. In this cohort, dogs with no abnormalities detected on preoperative EEG had favorable outcomes during their hospitalization.