Brainstem auditory evoked potentials during procaine toxicity in dogs

Although the toxic effect of local anaesthetics on the activity of cerebral cortex has been extensively studied, little is known about their toxic effect on brainstem. Accordingly, the influence of procaine on brainstem auditory evoked potentials (BAEPs) and on the electroencephalogram (EEG) was observed in 15 dogs. After the administration of procaine (15 mg · kg−1, iv), the amplitudes of wave I (1.88 ± 0.56 vs 2.06 ± 0.61 μV, mean ± SD) and wave II (1.91 ± 0.41 vs 2.06 ± 0.46 μV) in BAEPs increased (P < 0.05), while the amplitudes of wave III (0.97 ± 0.27 vs 0.81 ± 0.24 μV), wave IV (1.15 ± 0.43 vs 0.85 ± 0.29 μV) and wave V (1.04 ± 0.46 vs 0.92 ± 0.41 μV) were decreased (P < 0.05), and both the I–III inter-peak latency (1.57 ± 0.04 vs 1.70 ± 0.07 msec) and III–V inter-peak latency (2.15 ± 0.09 vs 2.35 ± 0.12 msec) were prolonged (P < 0.01). The EEG changed from an awake pattern to seizure activity. These results suggest that the electrical activity of the brainstem auditory pathway is suppressed even when the cerebral cortex is in an excitatory slate at the convulsive stage of procaine toxicity.