The present study was designed to test the hypothesis that dexmedetomidine added to ropivacaine for interscalene brachial plexus blocks for elective shoulder surgery would enhance the duration and effect of analgesia when compared with ropivacaine alone, and their influence on serum IL-6, cortisol, IL-1beta, IL-8, and substance p.

Background The incidence of severe postoperative pain after shoulder surgery is 30% to 70%.The postoperative pain should be relieved for early rehabilitation and recovery. Patient-controlled analgesia (PCA) with opiate therapy may control some of the postoperative pain, but it has several side effects such as nausea, vomiting, and dizziness, which can prevent early discharge. Conversely, there are several regional blocks to control postoperative pain. Interscalene brachial plexus block (ISB) is known as one of the most effective regional blocks for shoulder surgery, but it has relatively short duration of effect.

Dexmedetomidine (DEX), a selective agonist of α2-adrenergic receptors, can be an effective adjuvant to local anesthetics for peripheral nerve block. Preclinical and clinical studies have described prolonged duration of analgesia when dexmedetomidine was added to bupivacaine, levobupivacaine, or ropivacaine for peripheral perineural blocks.

Pro-inflammatory cytokines, such as interleukin-6 (IL-6), shows a high association with acute pain because they sensitize the nervous system. IL-6 levels in the plasma are detectable 60 minutes after injury, peaking at 4-6 hours, and are proportional to tissue injury.

Increased plasma cortisol concentrations can be detected within 15 minutes following exposure to a stressor. And several biomarkers related to pain have been studying.

Method 50 patients with rotator cuff tears who had undergone arthroscopic rotator cuff repairs were enrolled in this study. Rotator cuff tears were diagnosed by preoperative magnetic resonance imaging, and the size of the rotator cuff was confirmed at the time of arthroscopic operation. Indication for surgery was a symptomatic full-thickness rotator cuff tear or a partial thickness rotator cuff tear of more than 50% thickness in case of failed conservative therapy. Twenty-five patients were randomly allocated to group 1 and received both ISB with 8mL of ropivacaine with 100 μg (1ml) of dexmedetomidine . The other 25 patients were allocated to group 2 and received ISB with 8mL of ropivacaine with 1ml of normal saline.

Power analysis indicated that a total sample size of 46 patients (23 patients in each cohort) would provide a statistical power of 99% with a 2-sided a level of 0.05 to detect significant differences in the visual analog scale (VAS) score at 6 hours postoperatively, assuming an effect size of 0.88 (mean difference, 2.46, standard deviation, 2.8). This was based on the mean and standard deviation of the VAS at 6 hours postoperatively observed in a pilot study of 20 patients.

Double-blinded randomization was performed as follows. The remaining 50 patients were randomly assigned to 1 of 2 groups depending on the additional dexmedetomidine. Randomization was performed with a computerized random-sequence generator by an independent nurse who prepared a syringe for added dexmedetomidine or saline according to the assignment. The patients and all the medical staff who participated in the operation were blinded of the assignment.

VAS pain score, IL-6, cortisol, IL-1beta, IL-8, and substance p, height, and weight were checked preoperatively. All ISB were performed preemptively under ultrasonographic guidance. After sterile preparation and draping of the injection area, the structures of the brachial plexus were identified using ultrasound (Sonosite M-Turbo 13 mHz linear probe; Sonosite Corp, Bothell, Washington). Injections were performed using an out-of-plane technique using a plexus needle (Plexus Nano Line Uniplex, 22 gauge, 50 mm; Pajunk Corp, Geisingen, Germany). Nerve stimulation was not conducted.

PCA was set at a fixed dose (fentanyl, 0.05 mg/kg loading dose and 0.03 mg/min/kg continuous dose) to remove the effect of a variable amount of PCA. VAS pain score, IL-6, cortisol, IL-1beta, IL-8, and substance p, were checked 1, 6, 12, 24, and 48 hours postoperatively. VAS pain score was selected from 0 to 10, with 0 being no pain and 10 being the most severe pain that the patient had ever experienced.

Inclusion Criteria:

1. a definite rotator cuff tear that needed repair seen on preoperative magnetic resonance imaging
2. acceptance of arthroscopic surgery including rotator cuff repair
3. age more than 20 years,
4. acceptance of preemptive regional block , PCA and blood sampling after 1 ,6, 12, 24, 48 hour postoperatively. .

Exclusion Criteria:

1. they did not undergo arthroscopic rotator cuff repair
2. they stopped PCA before 48 hours postoperatively because of associated side effects
3. there was a history of a previous shoulder operation or fracture
4. there was a concomitant neurologic disorder around the shoulder
5. refusal of blood sampling.