Background:Preemptive analgesia is the initiation of analgesic regimen before the onset of nociceptive stimulation, preventing the amplification of pain due to peripheral and central sensitization and thereby reducing subsequent pain. Preemptive analgesia of dexmedetomidine (DEX) in the epidural and subarachnoid space can effectively prevent the central sensitization, and significantly reduce the phantom limb pain, residual pain after one year of lower limb amputation.

Objective: To investigate the per-operative effects of DEX preemptive analgesia.

Method:The patients scheduled noncardiac surgery undergoing general anesthesia were selected and divided into DEX group and Placebo group randmized. The DEX group was continuously pumped at 1.5 μg /(kg·h) for 15 minutes before induction, and 15min after induction. The Placebo group was infused with equal amounts of normal saline.The Coprimary efficacy outcome was a composite of analgesia effect, one is the Compliance Rate of IOC2 target in intra-operation, another is the the rate of none-to-slight post-operative pain assessed with the p-NRS≦3 at 12 hours after surgery [Pain numeric rating scale was assessed with the (Numeric Rating Scale, p-NRS)].

Background:Preemptive analgesia is the initiation of analgesic regimen before the onset of nociceptive stimulation, preventing the amplification of pain due to peripheral and central sensitization and thereby reducing subsequent pain. Preemptive analgesia of DEX in the epidural and subarachnoid space can effectively prevent the central sensitization, and significantly reduce the phantom limb pain, residual pain after one year of lower limb amputation.

Objective: To investigate the per-operative effects of DEX preemptive analgesia.

Inclusion Criteria:

• 18 years to 85 years old,
• body mass index (BMI,calculated as weight in kilograms divided by height in meters squared): 18.5~35.
• ASA (American Society of Anesthesiologists) Grade I- III;
• Scheduled for non-cardiac surgery undergoing general anesthesia
• expected duration of operation 0.5~3 h.

Exclusion Criteria:

• disagreed to participate;
• body mass index (BMI) of greater 35
• American Society of Anesthesiologists (ASA) classification 4 or above;
• previous severe central nervous systemheart, liver, kidney or and lung dysfunction ;
• diagnosed neuropsychological disorders, that is, schizophrenia, epilepsy, Parkinson's disease, myasthenia gravis，Alzheimer's disease and other autonomic disorders of patients affecting EEG outcomes;
• comatose, dementia, or language barrier which impeded communication and assessment;
• history of neurosurgical procedures;
• Systolic blood pressure continuously lower than 85mmHg or higher than 180mmHg; heart rate continuously lower than 45 times / min; sever arrhythmia need intervation and implantable pacemaker.