Monitoring Hypertensive Patients's Cerebral Oxygen Saturation (MHPCOS)

Inclusion Criteria:

• patients have hypertension more than 3 year,whether well-controlled or uncontrolled,
• scheduled for major abdominal surgery for at least 2 h
• under general anesthesia
• American Society of Anesthesiologists（ASA）physical status : II ~ III
• Age > 30

Exclusion Criteria:

• pre-existing cerebral pathology for example episodes of cerebral ischemia or stroke;
• ASA physical status >IV
• hepatic failure
• renal failure
• preoperative Mini-Mental State Examination (MMSE) score less than 24
• a history of cardiovascular surgery or craniotomy
• cardiac failure
• respiratory failure