Patients will be randomly allocated into two groups (Group A and Group B) using a computer-generated table.

Group A: Dexmedetomidine will be used as an adjuvant to propofol-based TIVA.

      Group B: Fentanyl will be used as an adjuvant to propofol-based TIVA

All patients will be shifted to the operating room, where ASA standard monitors will be attached and heart rate (HR), mean arterial pressure (MAP), systolic blood pressure (SBP), diastolic blood pressure (DBP), oxygen saturation (SpOâ‚‚) and electrocardiogram (ECG) will be noted. BIS monitoring sensors will be attached to monitor the depth of anaesthesia. BIS monitoring consists of a sensor, a digital converter and a monitor. It involves the application of four electrodes on the forehead, which pick up signals from the cerebral cortex and transfer them to the digital signal converter. The forehead will be cleaned with an alcohol-based solution and digital pressure applied over the sensor leads before placement (23).

All the patients will be pre-oxygenated with an appropriately sized face mask with 100% oxygen for 3 minutes. Induction will be done according to the allocated group.

Group A: Patients in this group will receive a loading dose of intravenous dexmedetomidine 1 mcg/kg over 10 minutes followed by a maintenance dose of 0.5 mcg/kg/hr. Titrated doses of intravenous propofol will be administered as a bolus to achieve BIS 40-60. After checking the ability to mask ventilate, 0.1mg/kg vecuronium will be administered intravenously. After three minutes of mask ventilation, the airway will be secured with an appropriately sized endotracheal tube. Dexmedetomidine infusion will be continued at the maintenance dose of 0.5mcg/kg/hr. Propofol infusion will be initiated at 100mcg/kg/min and titrated to BIS 40-60.

 Group B: Patients in this group will be induced anaesthesia with 2mcg/kg of intravenous fentanyl followed by intravenous propofol 2-2.5mg/kg. After checking the ability to mask ventilate, 0.1mg/kg vecuronium will be administered intravenously. After three minutes of mask ventilation, the airway will be secured with an appropriately sized endotracheal tube. Fentanyl infusion will be initiated at a dose of 1mcg/kg/hr. Propofol infusion will be initiated at 100mcg/kg/min and titrated to BIS of 40-60. 

 The hemodynamic parameters such as HR, MAP, SBP and DBP will be noted throughout the surgery at predetermined intervals. Urine output will be monitored at hourly intervals. All patients will be ventilated with an oxygen and air mixture at a ratio of 1:1, 6-8 ml/kg of tidal volume, I: E ratio of 1:2, positive end-expiratory pressure (PEEP) of 5cm of Hâ‚‚O and the respiratory rate adjusted to maintain an end-tidal carbon dioxide (EtCOâ‚‚) of 30-35mmHg. Intermittent intravenous vecuronium boluses will be given to all the patients. Fluid management will be based on standard hemodynamic monitoring: aiming to sustain a MAP ≥ 65 mmHg, systolic pressure variation (SPV) below 13%, hematocrit (HCT) ≥ 30% and ensuring urinary output ≥ 0.5 ml/kg/hour. The MAP will be maintained at a level of ± 20% compared to the baseline. Baseline MAP will be defined as the average value of the first three MAP measurements from preoxygenation to induction. If the MAP increases or decreases by more than 20% of baseline values, the rate of fluid infusion will be adjusted, and a vasopressor or an antihypertensive agent, like esmolol or labetalol, will be given accordingly. The intraoperative nasopharyngeal temperature will be maintained between 36 Â°C and 37 Â°C. The amount of blood loss during the surgery will be assessed from the collection container in the suction apparatus, craniotomy drape and the mopping pads used during the surgery. The total amount of fluids given to the patient throughout the surgery will be noted.

 Propofol infusion will be discontinued after completion of scalp sutures. The oropharynx will be gently suctioned using a soft suction catheter. The neuromuscular block will be reversed with intravenous neostigmine (0.05 mg per kg) & glycopyrrolate (0.01 mg per kg). The trachea will be extubated after objective extubation criteria are met. The entire duration of the surgery will be noted. Patients, who are not extubated, will be shifted to the intensive care unit (ICU).