In patients undergoing craniotomy, 0.9% normal saline is commonly administered in order to reduce cerebral edema. Excessive administration of 0.9% normal saline has been to reported to cause hyperchloremic metabolic acidosis. On the other hand, hypovolemia due to insufficient fluid replacement for perioperative loss can also result in metabolic acidosis by lactic acid accumulation. However, the guideline for perioperative fluid management has not been yet established. The investigators hypothesized that intraoperative fluid management according to SVV(Stroke Volume Variation)could reduce perioperative metabolic acidosis compared to those by CVP(Central Venous Pressure). Therefore, the study is trying to determine if intraoperative fluid administration based on SVV could reduce metabolic acidosis when compared with CVP in patients undergoing craniotomy due to brain tumor who receive 0.9% normal saline as main fluid regimen.

Inclusion Criteria:

• patients undergoing craniotomy due to brain tumor
• American Society of Anesthesiologists physical status I or II
• aged from 20 to 65

Exclusion Criteria:

• compromised cardiopulmonary function
• diabetes mellitus
• symptom or sign with increased intracranial pressure
• liver or renal disease
• pre-existing metabolic acidosis
• pregnant or breast-feeding
• patients who cannot understand the statements for subjects