EFFECTS OF ALFENTANIL ON THE EQUINE ELECTROENCEPHALOGRAM DURING ANESTHESIA WITH HALOTHANE IN OXYGEN

Opioids have variable effects on the minimum alveolar concentration of inhaled anaesthetics in the horse. During halothane anaesthesia at an end-tidal halothane concentration between 0.75 and 0.85 per cent, the electroencephalogram (EEG) frequency power spectrum and the auditory evoked potential were recorded continuously in eight ponies during an infusion of approximately 40 mu g kg(-1) alfentanil over five minutes. and for a further 55 minutes. The spectral edge and median frequency of the EEG and the mid-latency of the auditory evoked potential at the time of maximum change of these variables were compared with those re corded before the start of the infusion. The mean (SD) spectral edge a nd median frequencies were reduced by 26 (5) per cent and 36 (6) per c ent respectively. The mid-latency of the auditory evoked potential did not change. These cortical effects of alfentanil in the horse are qua litatively the same as in other species, suggesting that the alfentani l-induced excitement observed in horses is not of cortical origin.