Background and Goal of Study:
Bispectral Index (BIS) monitoring is one of the most popular techniques for evaluating the depth of anesthesia in human. Moreover, BIS is becoming a useful tool for estimating the sedation level. Dexmedetomidine (Dex) shows preferable profiles for perioperative sedation, and studies are increasing; however, there is scarce reports studying the effect of Dex on BIS values in experimental animals. In the current preliminary study, we investigated the validity of BIS monitoring in awake and sedated rats using Dex.

Material and Methods:
Male SD rats weighing 220-240 g were used. The rats were received brief anesthesia and were attached the 4 pierced electrodes on the head. Each rat was given 48-h recovery period. The electrodes were connected the leads and EEG signal was analyzed by Vista A-3000 (Nihon Kohden, Tokyo, Japan).

Study 1: The rats were administered Dex. The infusion rates were changed every 15 minutes and was randomly set at 0 (control), 20, 40 and 80 µg/kg/h.
Study 2: The rats were infused Dex at 40 µg/kg/h. After the stabilization of BIS value, each animal was received gentle stimuli (patting).
The BIS Index, spectral edge frequency 95% and amplitude were recorded after the equilibrium period. The results were analyzed using ANOVA and a P value less than 0.05 was considered as statistically significant.

Results and Discussion:
Dex significantly reduced BIS values in a dose dependent manner (Table, Fig. 1.). In Study 2, the BIS value was temporarily increased immediately after the patting stimuli (Fig. 2.). The changes in BIS values indicated the sedation and anesthesia states of the rats.

Conclusion:
We evaluated the changes in BIS values in awake, anesthetized and sedated rats. BIS monitoring might be useful and reliable tool for evaluating the effect of drugs modifying the activity of central nervous system in experimental animals.


06 / Bispectral Index and encephalogram monitoring in rats during dexmedetomidine infusion