Comparison of analgesic techniques for antler removal in halothane-anaesthetized red deer (Cervus elaphus): Electroencephalographic responses

Abstract

Objective: To provide evidence for an analgesic effect of antler pedicle compression or lidocaine 'ring block' by comparing changes in median and spectral edge frequencies and total electroencephalographic (EEG) power during the application of each technique followed by antler removal. Animals: Twenty-nine 2-year-old red deer (Cervus elaphus) stags weighing 106-131 kg each were used in this study. Stags were carrying immature growing antler suitable for commercial harvest. Materials and methods: Anaesthesia was induced using propofol (8.25 ± 1.28 mg kg-1) and ketamine (2.18 ± 0.15 mg kg-1) and maintained with halothane in oxygen. End-tidal halothane (FE′HAL), expired CO2 tension (PE′CO 2), SpO2, EEG, ECG, and direct arterial blood pressures were recorded continuously. Respiratory rate and somatic responses were recorded at specific time points. After stabilization of anaesthesia (FE′HAL was approximately 0.8%) baseline data were recorded. Stags were randomly allocated to one of three treatment groups; control, local anaesthesia, or compression band. One antler was removed 4 minutes after the application of treatment. Electroencephalographic responses to application of treatment and antler removal were analysed using area under the curve (AUC) analysis. Mean AUC was compared between groups using ANOVA, and when significant differences were found, groups were compared post hoc with two-tailed t-tests. Significance levels were set at p ≤ 0.05. Results: Median frequency (F50) was increased during antler removal in the control group and during both application and antler removal in the compression group. In the lidocaine group, F50 was decreased during both application and antler removal. Spectral edge frequency (F95) was increased during the antler removal period in the control group and during both application and antler removal in the compression group. In the lidocaine group, F95 was decreased in the application time period. Total EEG power (Ptot) was decreased in the removal period in the control group. In the compression group, Ptot was decreased in the removal period. In the lidocaine group, Ptot was decreased in the application period. There were no significant differences in EEG variables between antler removal in the control group and application of compression (p = 0.19-0.96). Conclusions: These data suggest that lidocaine 'ring block' of the antler pedicle provides adequate analgesia for velvet antler removal. The use of antler pedicle compression bands represents a noxious stimulus in its own right and is not as protective as lidocaine 'ring block' against the noxious stimulus of surgical antler removal. Clinical relevance: Compression of the antler pedicle has been recommended as an alternative to lidocaine 'ring block' for velvet antler removal. The results of this study suggest that antler pedicle compression is noxious. In addition, antler pedicle compression offers less effective analgesia than lidocaine 'ring block'. © Association of Veterinary Anaesthetists, 2005.