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

Abstract

ObjectiveTo evaluate Fourier-transformed electroencephalographic (EEG) variables, mean arterial blood pressure (MAP) and pulse rate as nociceptive indicators in isoflurane-anaesthetized horses. AnimalsFive standardbred and three Norwegian cold-blooded trotter stallions undergoing castration, aged 2–4 years, mass 378–538 kg. Materials and methodsAll 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. ResultsA significant rise in MAP and a fall in pulse rate were found. No significant change was found in any EEG variable. Conclusion/clinical relevanceOf the variables evaluated, MAP seems to be the most sensitive and reliable indicator of nociception in isoflurane-anaesthetized horses.