Group 1 will include 20 patients aged 18 years and over, American Society of Anesthesiologist (ASA) II-III class, who will undergo supratentorial tumor surgery, and Group 2 will include 20 patients who will undergo pituitary surgery without mannitol. Total intravenous anesthesia (TIVA) will be adjusted to propofol 4 µg/dl and remifentanil 2-4 µg/dl with target-controlled infusion pumps. In the mannitol group, 2.5 ml/kg (0.5 g/kg) will be given to all patients 20 minutes after induction and the mannitol infusion will be adjusted to be 10 minutes.In Group 2, mannitol will not be used and 2.5 ml/kg isotonic will be administered in 10 minutes. Both blood and urine samples will take for measurement to propofol levels.