Comparison of bispectral index and spectral entropy during isoflurane and medetomidine general anaesthesia in horses.
Authors: Navarrete-Calvo Rocío, Morgaz Juan, Gómez-Villamandos Rafael J, Quirós-Carmona Setefilla, Domínguez Juan M, Ruiz-López Patricia, Granados María M
Journal: Equine veterinary journal
Summary
# Editorial Summary: Assessing Anaesthetic Depth in Equine Surgery Monitoring central nervous system depression during equine general anaesthesia remains clinically important for ensuring adequate surgical conditions whilst minimising overdosing and complications. Researchers compared two electroencephalographic methods—bispectral index (BIS), which is already established in equine practice, and spectral entropy (specifically state and response entropy), which had not previously been evaluated in horses—by recording measurements across sedation, intraoperative and recovery phases in 35 ASA I–II horses receiving medetomidine and isoflurane. During surgical plane anaesthesia, BIS readings were substantially higher (53.4 ± 11.2) than both response entropy (35.1 ± 7.1) and state entropy (27.4 ± 4.8), with poor correlation between methods (ICC 0.56 for BIS versus response entropy; 0.43 for BIS versus state entropy) and no meaningful agreement between them. Whilst spectral entropy effectively distinguished between different anaesthetic phases—showing significantly lower values during surgery—the two monitoring approaches appear to measure different neurophysiological parameters rather than providing interchangeable information. Practitioners should recognise that BIS and spectral entropy are not equivalent tools for assessing depth of anaesthesia; further work is needed to establish clinical reference ranges and optimal applications for spectral entropy in equine anaesthesia protocols.
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Practical Takeaways
- •Spectral entropy monitoring can reliably track depth of anaesthesia across different phases of equine surgery, though it produces different absolute values than BIS
- •BIS and spectral entropy should not be used interchangeably—they measure CNS depression differently in horses and require separate interpretation protocols
- •Spectral entropy may offer a useful alternative monitoring tool during equine general anaesthesia, particularly during maintenance phase, but skin preparation requirements and recovery period limitations must be considered clinically
Key Findings
- •State entropy, response entropy, and EMG showed significant differences across sedation, intraoperative, and recovery periods (P < 0.001)
- •BIS values (53.4 ± 11.2) were significantly higher than response entropy (35.1 ± 7.1) and state entropy (27.4 ± 4.8) during surgical plane anaesthesia (P < 0.001)
- •Intraclass correlation between BIS and response entropy was 0.56 and between BIS and state entropy was 0.43, with no concordance between methods
- •Spectral entropy can detect different anaesthetic phases with lowest values during intraoperative period, but correlates poorly with BIS monitoring