Dexmedetomidine Reduces Sevoflurane MAC-BAR During Pneumoperitoneum

This clinical trial aims to learn the impact of dexmedetomidine on the minimum alveolar concentration blunting the adrenergic response (MAC-BAR) of sevoflurane to carbon dioxide pneumoperitoneum in patients undergoing laparoscopic cholecystectomy. It will also learn about the effect of dexmedetomidine on hemodynamic parameters. The main questions are: * Does dexmedetomidine reduce the MAC-BAR of sevoflurane required to suppress the sympathetic response to carbon dioxide pneumoperitoneum? * Would dexmedetomidine administration dose-dependently reduce the minimum alveolar concentration blunting the adrenergic response of sevoflurane required to suppress the sympathetic response to carbon dioxide pneumoperitoneum? Researchers will compare low-dose dexmedetomidine to high-dose dexmedetomidine to see if dexmedetomidine works to treat postoperative negative behavior change and emergence delirium. Participants will: * Take intravenous dexmedetomidine or 0.9% saline (a look-alike substance that contains no drug) * Study drug infusions were initiated 15 minutes prior to anesthesia induction, allowing a minimum of 30 minutes to elapse before surgical incision to achieve steady-state plasma and brain concentrations.