After obtaining written informed consent from eligible patients, and getting an approval from Ethics committee of Ahvaz Jundishapur University of Medical Sciences, a double-blind prospective, randomized study will be done among patients with Brain Tumor Surgery. Thirty four patients scheduled for general anesthesia will be received midazolam one mg intravenously five min before entering the operating room. Premedication will perform with fentanyl two micro gram/kg. General anesthesia will perform with 4 mg/kg sodium thiopental. Inclusion criteria: The parent's consent, Age between 18 and 60 years old, ASA class I. Exclusion criteria: Previous complications with general anesthesia, Heart disease, Metabolic disorders, Chronic alcohol consumption and Brain herniation. Patients will be randomly allocated into two groups according to table of random numbers. Groups "one" and "two" will be received 5 ml/Kg mannitol(20%) Intravenous or 2.5 ml/Kg hypertonic saline(5%) Intravenous at the beginning of the surgery, respectively. The amount of electrolytes (sodium, potassium, chloride) and bicarbonate will be measured before surgery, 120 minutes after the start of surgery and at the end of the surgery.