Patients having lumbar spinal fusion often complain about severe postoperative pain and postoperative rehabilitation process can be affected negatively. Postoperative pain that cannot be well controlled may lead to delayed mobilization, pulmonary and thromboembolic complications, prolonged hospital stays, and chronic pain syndromes. Pain after spinal surgery can arise from several different tissues, such as the vertebrae, disks, ligaments, dura, facet joint, muscle, fascia, and subcutaneous and cutaneous tissues.

Ultrasound-guided lumbar erector spinae plane block (ESPB) has been shown to reduce postoperative pain in patients undergoing posterior lumbar interbody fusion (PLIF). However, the duration of analgesia after single-shot ESPB with commonly used local anesthetics is reported to be no more than 12 h, which often not long enough to provide satisfactory postoperative pain relief, as the pain typically lasts for several days. Compared with perineural route, intravenous additives to local anesthetics are commonly accepted as its safety and efficiency have been reported. Moreover, co-administration of intravenous dexamethasone and dexmedetomidine significantly prolonged the time to first rescue analgesic request after single-shot interscalene brachial plexus block. However, more data are needed especially for lumbar ESPB.

Inclusion Criteria:

1. Age 18-65 yrs
2. American Society of Anesthesiologists physical statusⅠ-Ⅲ
3. Involvement of ≤3 spinal levels
4. Undergo elective posterior lumbar interbody fusion
5. Informed consent

Exclusion Criteria:

1. A known allergy to the drugs being used
2. Pre-existing neuropsychiatric disorders or language barrier
3. Analgesics intake, history of substance abuse
4. Contraindications to peripheral nerve block
5. Acute cerebrovascular disease
6. Severe liver failure
7. Uncontrolled low blood pressure
8. Sinus bradycardia or atrioventricular block