Effects of thiopentone on the equine electroencephalogram during anaesthesia with halothane in oxygen |
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| Authors: | Cb Johnson M Bloomfield Pm Taylor |
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| Affiliation: | 1. Department of Biochemistry, University of Missouri, Columbia, MO, USA;2. Department of Higher Education, Shimla, Himachal Pradesh, India;3. Department of Biosciences, Himachal Pradesh University Shimla, India;4. Department of Biotechnology, Dr Y. S. Parmar University of Horticulture and Forestry, Neri Campus, Himachal Pradesh, India;5. Centre for Chemistry and Biotechnology, Deakin University, Geelong Campus, VIC, Australia;1. Kennedy Institute of Rheumatology, Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, United Kingdom;2. Department of Bioengineering, Imperial College London, United Kingdom |
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| Abstract: | ObjectiveTo characterise the effects of thiopentone on the equine electroencephalogram during halothane anaesthesia.Study designProspective controlled study.AnimalsEight healthy Welsh mountain pony geldings between 5 and 9 years old and weighing between 270 and 330 kg (mean 301 kg).MethodsAnaesthesia was induced with thiopentone and maintained using halothane in oxygen. End tidal halothane was maintained above 0.75 and below 0.85%. EEG was recorded continuously and a binaural broad band click stimulus was provided throughout the experiment at 6.1224 Hz. An infusion of 500 mg thiopentone was given over 5 minutes. Samples were taken for blood gas analysis and plasma thiopentone assay (HPLC) 5 minutes prior to the start of the infusion and at 3, 5, 7, 10, 15, 20, 30, 45 and 60 minutes. The median and 95th percentile of the EEG were calculated using standard statistical techniques and the mid-latency of the auditory evoked response was generated. The values of EEG variables at each time point were compared to the average value for the 15 minute period before the infusion was started. Arterial blood gas values and plasma thiopentone concentration were compared to the baseline sample taken prior to the start of the infusion. Comparisons were made using analysis of variance for repeated measures followed by Dunnett's test if a significant difference was detected.ResultsThe peak serum plasma concentration was 14.5 ± 2.4 μg mL−1 (mean ± SD) occurring 5 minutes after the start of the infusion. The 95% spectral edge frequency of the EEG decreased by a maximum of 27.4 ± 18.4% 7 minutes after the start of the thiopentone infusion. No changes were seen in median frequency of the EEG or the second differential of the middle latency auditory evoked response.ConclusionsThese results, coupled with the lack of antinociceptive action of thiopentone, support the hypothesis that median frequency of the EEG may be a useful indicator of nociception in anaesthetized animals.Clinical relevanceIf the EEG is to become a useful monitoring technique then it is important to understand the relative contribution of changing plasma concentrations of the agents used in anaesthesia. |
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| Keywords: | Encephalogram horses thiopentone |
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