The Application of Target Controlled Infusion of Etomidate Combined With Propofol in the Maintenance of Anesthesia During Brain Surgeries

Inclusion Criteria: * Aged between 60 and 80 years Brain surgeries Body weight is between 45 to 75 kg and body mass index is no more than 30 kg/m2 American Society of Anesthesiology (ASA) Physical Status: Ⅰ or Ⅱ Expected operation duration is between 3 and 5 h Signed informed consent form Exclusion Criteria: * Serious cardiac, cerebral(acute stroke, uncontrolled seizure, sever dementia), liver, kidney, lung, endocrine disease or sepsis History of general anesthesia within 24 h before the operation Long use of hormone or history of adrenal suppression Hyperlipidaemia Long use of psychotropic substances Systolic pressure is still under 90 mm Hg after twice given of vasopressor agent Suspected abuse of narcotic analgesia Patients need to use neuromuscular blocking drugs (except intubation) Allergy to trial drug or other contraindication Pregnant or breast-feeding women Attendance of other trial past 30 days