Routine non-invasive monitors will be attached to the patients. It will include noninvasive blood pressure (NIBP), heart rate (HR), electrocardiography (ECG), pulse oximetry (SpO2), end tidal carbon dioxide (EtCO2), state entropy (SE) and urine output. All patients will be preloaded with 10-15 ml/kg of normal saline Fentanyl will be administered intravenously in dose of 2µg/kg prior to induction followed by 0.5-2 µg/kg/hr as infusion. Patients in all 4 groups will be induced with propofol 1 to 2 mg/kg, titrated to loss of verbal response. Vecuronium 0.1 mg/kg will be given to facilitate tracheal intubation. Lignocaine 1.5mg/kg will be given 120 seconds prior to laryngoscopy. For beat to beat monitoring of blood pressure and blood gas analysis an arterial catheter will be placed after induction of anesthesia. Patients will be maintained according to the group allocation along with 50/50% Oxygen/Air. BIS monitoring will be used to maintain comparable depth of anesthesia in all the groups and will be titrated to keep SE in range of 40 to 60. Vecuronium will be given intermittently to maintain less than two twitches on neurostimulation. Body temperature will be maintained using forced air warming blanket.