The Effect of Analgesia Based Sedation Protocol on Brain Function of Critical Care Patients

Inclusion Criteria: * Signing a consent form * postoperative patient * Requirement for mechanical ventilation and anticipate time of mechanical ventilation more than 24 hours * Requirement for sedation * Age more than 18 and less than 85 years old Exclusion Criteria: * Unstable blood circulation * Heart rate less than 50 beats per minute * II ° ～ III ° atrioventricular conduct block * Intracranial lesions 、neurosurgical intervention and mental disability inability to cooperate; * Receipt of antipsychotics 、hypnotic drugs before surgery ; * Alcohol abuse; * Liver failure class Child-Pugh C; * Acute Respiratory Distress Syndrome; * Acute or chronic renal failure; * Other severe diseases ,septic shock; * Receipt of neuromuscular blocking drug; * Pregnancy and nursing woman; * Allergy to investigational drug or other contraindication.