Background and Goal of Study:
There is an ongoing debate whether the depth of anesthesia correlates to the incidence of postoperative cognitive impairment in elderly patients (1). However, many reports have not detected a significant association between the depth of anesthesia and postoperative cognitive dysfunction. To obtain fundamental data for our future experiments using aged rats, we investigated the effects of surgery under anesthesia with different concentrations of sevoflurane on the acquisition of spatial memory in adult rats.

Materials and Methods:
After approval of animal research committee, male, seven- to nine-month-old SD rats were randomly assigned to one of three groups; light anesthesia (LA: n=5), deep anesthesia (DA: n=5), and control group (C: n=5). Rats in the LA and DA groups received 2% and 4% inspired concentration of sevoflurane, respectively, plus 33% oxygen in nitrogen. A catheter was inserted into the tail artery in LA and DA groups. Norepinephrine was infused continuously in the DA group to maintain the same blood pressure as the LA group. The rats in both groups underwent fracture of the left femur and pinning surgery during anesthesia. Control group did not receive both anesthesia and surgery. Spatial learning was assessed on the 1,2,3,6, and 7th day after anesthesia and surgery by using Morris Water Maze, recording the time taken to reach the platform and the total swimming distance. Data were expressed as median (min, max), and Mann-Whitney U test was used for statistical analysis.

Results and Discussion:
There were no significant differences among the three groups in the time taken to reach the platform from the 1st to 6th day. However, on the 7th day, the time spent in the LA group (57 [51-89]) was significantly longer than those in the DA group (39 [6-46]) and C group (14 [5-27]). The swimming distance was significantly shorter in the DA than C group on the 2nd day, and longer in the LA group than C group on the 7th day.

Conclusion:
Acquisition of spatial cognitive function was similar among groups until 6 days after anesthesia and surgery, regardless of sevoflurane concentrations. However, on the 7th day, spatial cognitive dysfunction became apparent in the LA group. Our findings suggest that surgery under light anesthesia is likely to cause delayed central nervous system dysfunction.

References:
1) Chan MTV et al. Can J Anesth 64:574–580, 2017


01 / Effects of surgery under anesthesia with different concentrations of sevoflurane on the acquisition of spatial memory in adult rats