The aim of this study is to calculate desflurane consumption when combined with intraoperative dexmedetomidine infusion guided by bispectral index (BIS)

Forty patients will be randomly allocated into two equal groups as Group 'D' (Dexmedetomidine group) and Group 'P' (Placebo group) using computer generated random numbers. After arrival in the operating room, ondansetron 0.15 mg/kg intravenous (IV) will be given as a pre-medication. Ringer's acetate solution (500 ml) will be infused as a preload then at a rate of 6-8 ml/kg/h during surgery for supplying maintenance and deficit. Monitoring consisted of continuous electrocardiogram (EKG), non-invasive blood pressure (NIBP), pulse oximetry (SpO2), CO2 expired fraction (ETCO2), desflurane inspired fraction (FIdes), and desflurane expired fraction (ETdes) (Infinity Kappa, Dräger, Lübeck, Germany) will be attached to the patient. BIS module (InfinityR BISxTM SmartPodR, smoothing rate: 15 or 30 seconds, software revision: VF5) will also be attached for detection of consciousness level.

All patients will be preoxygenated with 100% oxygen for 3 minutes. The patients in group D will receive dexmedetomidine (2 ml diluted in 18 ml of saline) IV in a dose of 1 mcg/kg over10 minutes through infusion pump prior to induction. Group P patients will receive similar volume of normal saline over 10 min. The study drug and placebo infusions will be prepared by an anesthesiologist who is not involved in the study and the anesthesiologist recording the details is unaware of the type of infusion patients received. Anesthesia will be induced with IV fentanyl 1.5 μg/kg and propofol in a dose of 10 mg every 5 seconds until the BIS level dropped below 60 and confirmed with loss of response to verbal commands. In both groups, Atracurium 0.5 mg/kg IV will be administered, and trachea will be intubated. Fresh gas flow oxygen in air 30-40% at a rate of 3 L/min for 10 minutes will be administered then the flow will be decreased at a rate of 1 L/min using a closed system (Fabius GS, Dräger, Lübeck, Germany) and ventilation will be adjusted to maintain end-tidal carbon dioxide at 30-35 mmHg. Patients in study groups will receive the volatile agent at a concentration of 1 MAC (Minimum Alveolar Concentration). The MAC of desflurane is defined as an expired fraction of 6.0 vol%. Then the dial-up desflurane percentage will be adjusted to establish a BIS value between 40- 50. A maintenance dose of Dexmedetomidine infusion at 0.5 mcg/kg/hour made to 20 mL with normal saline will be administered in group D patients and a similar volume of normal saline will be administered in Group P, till the end of surgery. Top up doses of Atracurium will be given as needed. When heart rate and blood pressure exceeds 20% of baseline in spite of adequate level of anesthesia guided by BIS, boluses of 0.5 μg/kg will be given. While decrease in heart rate and blood pressure more than 20% of baseline, will be treated by ephedrine 5 mg.

In both groups, dexmedetomidine or saline will be stopped approximately 15-20 minutes before completion of surgery, diclofenac sodium 1 mg/kg will be given IM at the time of skin closure. Desflurane will be discontinued after skin closure in both groups. Reversal of neuromuscular blockade will be achieved with neostigmine 0.05 mg/kg and atropine 0.02 mg/kg. Tracheal extubation will be done when respiration is satisfactory and adequate muscle tone is achieved

Inclusion Criteria:

• American Society of Anesthesiologists (ASA) status of I and II
• undergoing elective laparoscopic cholecystectomy

Exclusion Criteria:

• history of psychiatric/neurological illness
• cardiovascular disease
• morbid obese patients
• pregnant and nursing women
• known allergic reaction to any of the study medication
• recent use of sedatives or analgesics