Benzodiazepines is a commonly uesd sedative medication,there are many reports that Benzodiazepines is associated with delirium ,but using of analgesia reduces benzodiazepines requirements .The purpose of this study is to determine whether analgesia based sedation protocol reduces the incident of delirium.

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.