Abstract
The performance of the cerebral state index (CSI) in reflecting different levels of isoflurane anaesthesia was evaluated in ten cats subjected to four end-tidal isoflurane concentrations (EtIso), each maintained for 15 minutes (0.8%, 1.2%, 1.6%, or 2.0% EtIso). The CSI, hemodynamic data, ocular reflexes, and eye position were recorded for each EtIso concentration. Pharmacodynamic analysis of CSI with EtIso was performed, as well as prediction probability analysis with a clinical scale based on the eye reflexes. The CSI values showed great variability. Between all parameters, burst suppression ratio showed the better fitting with the sigmoidal concentration-effect model (R 2 = 0.93) followed by CSI (R 2 = 0.82) and electromyographic activity (R 2 = 0.79). EtIso was the variable with better prediction of the clinical scale of anaesthesia (prediction probability value of 0.94). Although the CSI values decrease with increasing isoflurane concentrations, the huge variability in CSI values may be a strong limitation for its use in cats and it seems to be no better than EtIso as a predictor of clinical signs.
Highlights
Anesthetic depth monitoring is undergoing important innovations, especially with the recent introduction of new technological solutions, such as monitors that process the electroencephalographic (EEG) activity
The objective of this study is to test the capacity of the cerebral state index (CSI) to reflect different concentrations of isoflurane in cats, by analyzing its correlation with the clinical signs used to assess the depth of anesthesia and the dose-effect relationship with isoflurane concentration
Because all of the cats awoke at 0.8% end-tidal isoflurane concentrations (EtIso), it was not possible to analyze the data during the two minutes after the stabilization at this level and only the last values obtained in the 0.8% EtIso cats before awakening were used for analysis to represent the lowest concentration achieved in the study
Summary
Anesthetic depth monitoring is undergoing important innovations, especially with the recent introduction of new technological solutions, such as monitors that process the electroencephalographic (EEG) activity. There are only a few studies which evaluate the BIS for depth of anaesthesia assessment, by correlating its values with the anaesthetic concentration In those studies, BIS values were inversely and linearly related to end-tidal sevoflurane [4] and isoflurane concentrations but were consistently low suggesting that clinical BIS endpoints used to titrate anesthetic agents in humans may not be applicable to cats [5]. BIS values were inversely and linearly related to end-tidal sevoflurane [4] and isoflurane concentrations but were consistently low suggesting that clinical BIS endpoints used to titrate anesthetic agents in humans may not be applicable to cats [5] This possibility was supported in a previous study, which suggests that clinical BIS endpoints used in humans may not be used in cats, due to the fact that BIS in this specie varied between 5 to 32 with 1.5 to 0.8 MAC isoflurane [5]. Another potential advantage of this monitor is the fact that
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