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Open Access Relationship of Feline Bispectral Index to Multiples of Isoflurane Minimum Alveolar Concentration

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The study reported here was done to determine the relationship between bispectral index (BIS) values and minimum alveolar concentration (MAC) multiples of isoflurane in cats. Isoflurane MAC was determined using the tail-clamp method in eight domestic cats. Ten days later, the cats were anesthetized a second time with isoflurane at each of five MAC multiples administered in random order. Ventilation was controlled and, after a 20-min equilibration period at each MAC multiple of isoflurane, BIS data were collected for 5 min and the median BIS value calculated. Data from each isoflurane MAC multiple were compared using analysis of variance for repeated measures, and statistical significance was set at P < 0.05. The MAC of isoflurane (mean ± 1 standard deviation) was 1.8% ± 0.2%. BIS values at 0.5 MAC could not be recorded due to spontaneous movement in all eight cats. BIS values at 2.0 MAC were confounded by burst suppression in seven of the eight cats. Over the range of 0.8 to 1.5 MAC, BIS values decreased significantly with increasing end-tidal isoflurane concentrations. Mean (± 1 standard deviation) BIS measurements were 32 ± 3 at 0.8 MAC, 20 ± 4 at 1.0 MAC, and 5 ± 3 at 1.5 MAC. Therefore, BIS values are inversely and linearly related to end-tidal isoflurane concentrations in anesthetized cats. However, the consistently low BIS values recorded in this study suggest that clinical BIS endpoints used to titrate anesthetic agents in humans may not be applicable to cats.

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Document Type: Research Article

Affiliations: 1: Department of Companion Animals, Atlantic Veterinary College, University of Prince Edward Island, Charlottetown, Prince Edward Island, PEI C1A 4P3, Canada 2: Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, Illinois 61802

Publication date: 2005-06-01

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  • Comparative Medicine (CM), an international journal of comparative and experimental medicine, is the leading English-language publication in the field and is ranked by the Science Citation Index in the upper third of all scientific journals. The mission of CM is to disseminate high-quality, peer-reviewed information that expands biomedical knowledge and promotes human and animal health through the study of laboratory animal disease, animal models of disease, and basic biologic mechanisms related to disease in people and animals.

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