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.

Laparoscopic (minimally invasive) surgery has several advantages over open surgery, including less tissue damage, faster recovery, and fewer complications. This has led to widespread use of laparoscopic techniques. However, the inflated carbon dioxide gas used to create the surgical space during laparoscopic surgery causes significant changes in the body's normal blood pressure and heart function.

The anesthetic drug sevoflurane is commonly used during these procedures, but higher doses are needed to adequately block the body's stress response to the inflated gas. The minimum alveolar concentration blunting the adrenergic response (MAC-BAR) measures the minimum anesthetic depth required to suppress the sympathetic/stress response in 50% of patients. Doctors use MAC-BAR values to help determine the appropriate anesthetic dose to maintain hemodynamic stability. Unfortunately, using higher sevoflurane doses to reach the necessary MAC-BAR increases the risk of low blood pressure, reduced heart function, and confusion after surgery.

The drug dexmedetomidine has properties that can help manage the body's stress response during surgery. Researchers wanted to see if dexmedetomidine could allow the use of lower, more stable doses of sevoflurane during laparoscopic procedures by reducing the body's reaction to the inflated gas.

The goal of this study was to evaluate how dexmedetomidine affects the MAC-BAR of sevoflurane needed to block the sympathetic/stress response to the inflated gas used in laparoscopic surgery.

Inclusion Criteria:

• 1. Aged 18-45 years.
• 2. American Society of Anesthesiologists (ASA) grade I - II.
• 3. Patients undergoing elective laparoscopic cholecystectomy.

Exclusion Criteria:

• 1. Inability to provide informed consent;
• 2. History of chronic pain or substance abuse;
• 3. Pregnancy;
• 4. Body mass index (BMI) ≥ 30 kg/m2;
• 5. Known allergies to the study medications;
• 6. Intake of medications within the last 72 hours that potential interfere with the determination of the MAC-BAR;
• 7. Any other condition deemed exclusionary by the investigators.

After publication, the individual deidentified participant data underlying published results, the study protocol, and the statistical analysis plan can be accessed upon reasonable request from the corresponding author.

The investigators would like to share the individual deidentified participant data from the three months following the publication of the main results.

All the individual participant data collected during the trial, the study protocol, the statistical analysis plan, and the clinical study report can be accessed with approval from the corresponding author.