• Daniela Campagnol, Francisco J Teixeira Neto, Eduardo R Monteiro, Suzane L Beier, and Antônio J A Aguiar.
• Department of Veterinary Surgery and Anesthesiology, Faculdade de Medicina Veterinária e Zootecnia, Universidade Estadual Paulista (UNESP), Botucatu, São Paulo, Brazil.
• Am. J. Vet. Res. 2007 Dec 1; 68 (12): 1300-7.

ObjectiveTo evaluate the correlation between the bispectral index (BIS) and end-tidal isoflurane (ET(ISO)) concentration and compare the use of 3 BIS sensor positions in dogs.Animals6 adult dogs.ProceduresMechanically ventilated dogs received pancuronium, and depth of anesthesia was altered by increasing ET(ISO) concentration from 1.5% to 2.3% and 3.0%. The BIS, suppression ratio (relative percentage of isoelectric electroencephalographic waveforms), and signal quality index (SQI) were recorded at each ET(ISO) concentration for each of 3 BIS sensor positions (frontal-occipital, bifrontal, and frontal-temporal positions).ResultsThe BIS and ET(ISO) concentration were poorly correlated; regardless of sensor positioning, mean BIS values did not change significantly as ET(ISO) was increased. At 3% isoflurane, regardless of sensor positioning, there was an increase in suppression ratio coincident with BIS < 40 in some dogs, whereas paradoxic increases in BIS (> 60) were recorded in others. Furthermore, at 3.0% isoflurane, the SQI was significantly lower for the bifrontal sensor position (compared with values for the other positions), but low SQI values prevented recording of BIS values from the frontal-occipital sensor position in 2 dogs. Overall, BIS values derived from the 3 sensor positions did not differ.Conclusions And Clinical RelevanceIn dogs, BIS values may not reflect changes in depth of isoflurane anesthesia in the absence of noxious stimulation. Of the 3 sensor positions, frontal-temporal positioning provided better correlation with changes in depth of anesthesia induced via changes in isoflurane concentrations. However, the sensor placements yielded similar results at SQI values > 50.

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