Objective measurement of hepatic encephalopathy in pigs by means of spectral analysis and evoked responses.

Objective measurement of hepatic encephalopathy by means of spectral analysis of the electroencephalogram (EEG), visual-evoked potentials (VEP) and brainstem auditory-evoked potentials (BAEP) was studied in pigs with ischemic hepatic necrosis. The mean dominant frequency (MDF) and the relative power of the delta frequency band (% delta power) showed significant changes with increasing encephalographic grades of encephalopathy: MDF dropped from 7.0 +/- 0.5 (grade 0) to 2.7 +/- 0.3 Hz (grade 3 encephalopathy) and % delta power increased from 52 +/- 7 (grade 0) to 83 +/- 6% (grade 3). The patterns of the VEP in pigs corresponded to those of the human VEP. However, significant differences in either latency time of the peaks or the peak amplitude with increasing stages of hepatic encephalopathy could not be found. The BAEP registered for pigs were reproducible but also were not as useful as spectral analysis for grading hepatic encephalopathy.