Hyperosmotic solutions of 1.5% and 3% NaCl are equally effective for brain relaxation and microcirculation during brain surgery. The effect of 1.5% NaCl on postoperative natremia and natriuresis is less pronounced.

All the patients meeting the study criteria will be randomized into two groups. After standardized induction to general anesthesia all patients will be given the infusion of hyperosmotic NaCl 5 ml/kg/BW during 30 min, group A 1.5% NaCl, group B 3% NaCl. Corticosteroids will be administered as usually. After dura opening the brain relaxation score will be assessed by surgeon (1 = completely relaxed, 2 = satisfactorily relaxed, 3 = firm brain, 4 = bulging brain), and the first measurement of the brain microcirculation provided by use of SDF probe in the area of the healthy brain, and of perifocal oedema. Both sites of investigation will be marked for the second measurement, which will be done after the end of tumor resection. Laboratory examinations: natremia preoperatively, natremia and osmolarity peroperatively 1 hour after NaCl infusion and at the end of surgery. Concentration of natrium will be examined in CSF after dura opening. Anesthesia management will be according to the standardised protocol, the patients will be awaken and extubated after the end of the procedure at the operating theatre.

Inclusion Criteria:

• peripheral supratentorial brain tumors or metastasis
• indication for osmotherapy
• ASA status I-III

Exclusion Criteria:

• reoperation
• osmotherapy prior to surgery
• preoperative natremia less than 135 mmol/l and more than 140 mmol/l
• GCS less than 14
• obstructive hydrocephalus