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Electroencephalographic and cardiovascular variables as nociceptive indicators in isoflurane-anaesthetized horses


Henning A Haga, Department of Companion Animal Clinical Sciences, The Norwegian School of Veterinary Science, PO Box 8146 Dep, N-0033 Oslo, Norway. E-mail:


Objective  To evaluate Fourier-transformed electroencephalographic (EEG) variables, mean arterial blood pressure (MAP) and pulse rate as nociceptive indicators in isoflurane-anaesthetized horses.

Animals  Five standardbred and three Norwegian cold-blooded trotter stallions undergoing castration, aged 2–4 years, mass 378–538 kg.

Materials and methods  All horses received intravenous (IV) detomidine (10 μg kg−1 IV) and butorphanol (0.01 mg kg−1 IV). Additional detomidine (4 μg kg−1 IV) was administered in the induction area. Anaesthesia was induced with ketamine (2.5 mg kg−1 IV) and diazepam (40 μg kg−1 IV), and maintained for 30 minutes with isoflurane (end-tidal concentration of 1.4%) vaporized in oxygen. The electroencephalogram, MAP and pulse rate were recorded for 15 minutes, beginning 5 minutes before skin incision. Differences between the mean values of recordings taken before, and during surgery were calculated and tested for significant differences using a two-sided Student's t-test.

Results  A significant rise in MAP and a fall in pulse rate were found. No significant change was found in any EEG variable.

Conclusion/clinical relevance  Of the variables evaluated, MAP seems to be the most sensitive and reliable indicator of nociception in isoflurane-anaesthetized horses.