• Eliseo Belda, Eliseo Beldao, Karen J Blissitt, Juliet C Duncan, Francisco G Laredo, Mayte Escobar Gil de Montes, and R Eddie Clutton.
• Departamento de Medicina y Cirugía Animal, Hospital Clínico Veterinario, Universidad de Murcia, Murcia, Spain.
• Vet Anaesth Analg. 2010 Jan 1;37(1):25-34.

ObjectiveTo record the bispectral index (BIS) when horses moved during either halothane or sevoflurane anaesthesia and when they made volitional movements during recovery from these anaesthetics.Study DesignRandomized prospective clinical study.AnimalsTwenty-five client-owned horses undergoing surgery aged 8.8 (+/- 5.3; 1-19) years (mean +/- SD; range).MethodsBaseline BIS values were recorded before pre-anaesthetic medication (BIS(B)) and during anaesthesia (BIS(A)) maintained with halothane (group H; n = 12) or sevoflurane (group S; n =13) at approximately 0.8-0.9 x minimum alveolar concentrations (MAC). Bispectral indices were recorded during the surgery when unexpected movement occurred (BIS(MA)), during recovery when the first movement convincingly associated with consciousness was observed (BIS(M1)) and once sternal recumbency was achieved (BIS(ST)).ResultsNo significant difference in BIS(M1) was found between halothane- (85 +/- 7; 75-93) and sevoflurane- (87 +/- 10; 70-98) anaesthetized horses although BIS(A) was significantly (p = 0.0002) lower in group S (62 +/- 7; 53-72) than group H (74 +/- 7; 60-84). Differences between BIS(M1) and BIS(A) were significant in sevoflurane (p = 0.00001) and halothane recipients (p = 0.002) but were greater in group S (25 +/- 9; 4-38) compared with group H (12 +/- 10; -9-25). In six of eight horses, BIS(MA) values ranged between those recorded during anaesthesia and at first movement.Conclusions And Clinical RelevanceBispectral indices appear to approximate levels of unconsciousness, suggesting that monitoring the BIS may assist equine anaesthesia. However, it does not predict intra-operative movement.

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