Abstract
Objective
To identify changes in the amplitude spectrum of the electroencephalogram (EEG) during
a standardized surgical model of nociception in horses.
Animals
Thirteen entire male horses and ponies referred to Division of Clinical Veterinary
Science, Bristol (n = 9) and Department of Clinical Veterinary Medicine (n = 4) for castration.
Materials and methods
Following pre–anaesthetic medication with acepromazine, anaesthesia was induced with
guaiphenesin and thiopental and maintained with halothane in oxygen. The EEG was recorded
continuously using subcutaneous needle electrodes. Additional monitoring comprised
ECG, arterial blood pressure, blood gas analysis, airway gases, and body temperature.
All animals were castrated using a closed technique. The raw EEG was analysed after
completion of each investigation and the EEG variables median frequency (F50), spectral
edge frequency (SEF) 95% and total amplitude were derived from the spectra using standard
techniques. The mean values of EEG variables recorded during a baseline time period
(recorded before the start of surgery) and castration of each testicle were compared
using analysis of variance for repeated measures.
Results
Total amplitude (Atot) decreased and F50 increased during castration of each testicle
compared to the baseline time period [(89.0 ± 7.8% testicle 1, 87.0 ± 7.8% testicle
2) and (110.0 ± 15.0% testicle 1, 109.0 ± 15.0% testicle 2), respectively]. Changes
in SEF 95% were not significant.
Conclusions
De–synchronization was identified in the EEG during the nociceptive stimulus of castration.
The results suggest that an increase in F50 may be a specific marker for nociception
in the horse.
Clinical relevance
Studies investigating the efficacy of analgesic agents in horses are limited by difficulties
in peri–operative pain assessment. This model, using EEG changes associated with nociceptive
stimulation, can be used to investigate the anti–nociceptive efficacy of different
anaesthetic agents in the horse.
Keywords
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Article info
Publication history
Accepted:
June 18,
2002
Received:
November 1,
2001
Identification
Copyright
© 2003 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia. Published by Elsevier Inc. All rights reserved.