Evaluation of spectral entropy monitor with different concentrations of isoflurane in Horses.
Authors: Navarrete-Calvo R, Morgaz J, Ruíz-López P, Gómez-Villamandos R J, Domínguez J M, Quirós-Carmona S, Granados M M
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Spectral Entropy Monitoring During Equine Anaesthesia Depth-of-anaesthesia monitors such as spectral entropy and bispectral index have proven valuable in human anaesthesia, yet their reliability in equine practice remains uncertain. Researchers anaesthetised ten healthy horses at three different isoflurane concentrations (0.9%, 1.2%, and 1.5%) whilst recording spectral entropy (response and state entropy), bispectral index, electromyography, and end-tidal isoflurane levels, then applied electrical nociceptive stimuli to assess how these parameters responded. All monitored variables—response entropy, state entropy, bispectral index, and electromyography—significantly increased when the nociceptive stimulus was applied; however, only electromyography reliably distinguished between the lowest (0.9%) and highest (1.5%) isoflurane concentrations, with marked reductions in muscle activity at deeper planes of anaesthesia. These findings suggest that whilst entropy-based monitors may detect acute nociceptive responses during equine general anaesthesia, they cannot reliably assess anaesthetic depth across clinically relevant isoflurane ranges, whereas electromyography remains a more robust indicator of both depth and nociception. For equine veterinarians relying on these monitors to guide intraoperative management, conventional assessment methods—including haemodynamic variables, respiratory patterns, and jaw tone—remain essential alongside any technological monitoring, particularly when titrating volatile anaesthetic agents.
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Practical Takeaways
- •Do not rely on spectral entropy or BIS monitors alone to assess anaesthetic depth or guide isoflurane dosing in horses—EMG monitoring appears more reliable for this purpose
- •If using these monitors, recognize they may help identify pain responses during surgery but cannot replace clinical judgment and other depth-of-anaesthesia indicators
- •Consider supplementary monitoring methods alongside spectral entropy/BIS when managing equine general anaesthesia to ensure adequate depth across different isoflurane concentrations
Key Findings
- •Spectral entropy (RE, SE) and BIS parameters increased significantly with nociceptive stimulus application but did not reliably distinguish between isoflurane concentrations of 0.9%, 1.2%, and 1.5%
- •EMG was the only parameter showing significant differences between EtIso0.9 and EtIso1.5 during early (72±23 vs 48±23, P=0.011) and late nociceptive phases (65±27 vs 43±23, P=0.022)
- •Current spectral entropy and BIS monitors are not useful for assessing anaesthetic depth in horses under the studied conditions
- •Spectral entropy and BIS monitors may be useful for detecting induced nociceptive stimuli in anaesthetized horses