Correlation between clinical signs of depth of anaesthesia and cerebral state index responses in dogs with different target-controlled infusions of propofol.

OBJECTIVE: To evaluate if the cerebral state index (CSI), measured by a Cerebral State Monitor (CSM), can predict depth of anaesthesia as assessed clinically or by estimated propofol plasma concentrations. STUDY DESIGN: Prospective clinical study. ANIMALS: Fourteen mixed breed dogs, weighing 24.5 ± 4.7 kg, scheduled to undergo neutering procedures. METHODS: Dogs were premedicated with 0.05 mg kg(-1) acepromazine intramuscularly. The CSM and cardiovascular monitoring equipment were attached. Anaesthesia was induced with propofol using a target controlled infusion (TCI) to varying plasma propofol targets (PropCp). Following endotracheal intubation the dogs were ventilated with oxygen. Anaesthetic maintenance was with propofol by TCI. A PropCp of 3 µg dL(-1) was set initially, then PropCps were increased in 1 µg dL(-1) steps to 7, 9 and then 11 µg dL(-1). Each PropCp was held constant for a 5 minute period, at the end of which depth of anaesthesia was classified using a previously evaluated scale of 'planes' based on palpebral and corneal reflexes and eye position. Cerebral state index (CSI), burst suppression (BSR) and electromyogram were measured at these time points. The prediction probability (PK) of these variables, or of the PropCp in predicting depth of anaesthesia was calculated. RESULTS: The PKs for predicting anaesthetic planes were 0.74, 0.91, 0.76 and 0.78 for CSI, BSR, EMG and PropCp, respectively. The PKs for PropCp to predict CSI, BSR and EMG were 0.65, 0.71 and 0.65 respectively. CONCLUSION AND CLINICAL RELEVANCE: The Cerebral State Monitor was able to detect very deep planes of anaesthesia when BSR occurs, but was not able to distinguish between the intermediate anaesthetic planes likely to be used in clinical anaesthesia.

Dogs mean arterial pressure and heart rate responses during high propofol plasma concentrations estimated by a pharmacokinetic model.

Propofol total intravenous anesthesia should provide stability of the cardiovascular system. In this study, mean arterial pressure and heart rate were evaluated in eight healthy dogs anesthetized with increasing rates of propofol. The cerebral state index (CSI) was studied as an additional parameter. Although the estimated propofol plasma concentration reached a maximal value of 15.3 µg ml(-1), no hypotension or bradycardia were observed. Exploration of each animal's data revealed high inter-individual variability regarding mean arterial pressure and heart rate. Considering the logarithmic of the concentration, a moderate depressant effect of propofol on mean arterial pressure was revealed in five dogs but the effect was not followed on heart rate.

Brain monitoring in dogs using the cerebral state index during the induction of anaesthesia via target-controlled infusion of propofol.

The aim of this study was to evaluate the correlation between the cerebral state index (CSI) and the estimated propofol plasma concentrations in dogs during induction of anaesthesia. Fifteen healthy dogs undergoing scheduled routine surgical procedures were enrolled in this study. Target controlled infusion (TCI) software, based on the pharmacokinetic model for propofol, was used to control the syringe pump and to estimate plasma propofol concentrations (PropCp) and the CSI values every five-seconds. Three electrodes placed in the centre of the forehead, on the left side of the forehead and on the left mastoid were used to collect the electroencephalographic (EEG) signal converted by the cerebral state monitor into the CSI. The cerebral electrical changes induced by increasing propofol concentrations appear to be detected by CSI monitoring in dogs. The negative correlation between CSI and PropCp demonstrates that the CSI could be used to assess electrical brain activity in dogs during the induction of anaesthesia with propofol.