The patients were randomized into 3 groups using a closed envelope method, group 1; mannitol 0.5 g.kg-1 and furosemide 0.5 mg.kg-1 (G1), group 2; mannitol 1 g.kg-1 and furosemide 0.5 mg.kg-1 (G2) and group 3; mannitol 0.5 g.kg-1 and placebo (G3). All medications were prepared by a single nurse in 100 mL of a 0.9 percent isotonic saline solution. After head fixation, all patients were administered with mannitol (over 20 minutes) and the study drug. Arterial blood gas (ABG) analysis (Cobas b 221 blood gas analyzer, Roche®, Basel, Switzerland) was made at 30 minute intervals in the first 2 hour and then again in the 6th, 12th and 24th hours after study drug administration. Blood sodium, potassium, chlorine, lactate levels and urine output were recorded in each intervals. Blood osmolarity measured levels were recorded before the study drug administration and 2nd hours. The brain relaxation score (BRS) was evaluated twice by the surgical team using a 4 point scale (1= very good, 2= good, 3= bad, 4= very bad); first, at the time of dura opening, and second, 30 minutes after the administration of the study drug.