The bispectral index during recovery from halothane and sevoflurane anaesthesia in horses

Abstract

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 (BISB) and during anaesthesia (BISA) maintained with halothane (group H; n = 12) or sevoflurane (group S; n =13) at approximately 0.8–0.9 × minimum alveolar concentrations (MAC). Bispectral indices were recorded during the surgery when unexpected movement occurred (BISMA), during recovery when the first movement convincingly associated with consciousness was observed (BISM1) and once sternal recumbency was achieved (BISST). ResultsNo significant difference in BISM1 was found between halothane- (85 ± 7; 75–93) and sevoflurane- (87 ± 10; 70–98) anaesthetized horses although BISA was significantly (p = 0.0002) lower in group S (62 ± 7; 53–72) than group H (74 ± 7; 60–84). Differences between BISM1 and BISA 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, BISMA 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.