Intraoperative Pain and Quality of Surgical Block During Shoulder Surgery Assessed by NOL Index

The main hypothesis of this study is that the suprascapular block combined with a posterior cord block is not inferior to the interscalene brachial plexus block in terms of intraoperative analgesia. We postulate that intraoperative opioid requirements will not differ significantly in patients who receive either block.

Our secondary objectives will consist in looking at the differences in intraoperative anesthetic consumption, NOL index alterations, postoperative opioid consumption, pain scores, arm motor block, diaphragmatic paresis, patient satisfaction and time for readiness to discharge from PACU. We hypothesize that these outcomes will be similar in both groups, with the exception of a potential reduction in arm motor block and diaphragmatic paresis in the combined suprascapular and posterior cord block group.

After having obtained institutional ethics board approval of the study, patients older than 18 years old, scheduled for a first elective shoulder arthroscopy under general anesthesia will be screened in the pre-anesthesia clinic. They will be approached and the whole study procedures will be explained extensively. Interested patients will be invited to sign the consent form (see appendix). Patients will have the right to opt out at any time. The investigators will meet the patients again on the morning of the surgery to address any concerns. After consent, a study number will be allocated to the patient in ascending order.

Two groups will be evaluated:

• Group A: single shot US-guided suprascapular nerve block with 5 mL ropivacaine 0.5%, then single shot US-guided posterior cord block with 10 ml ropivacaine 0.5%.
• Group B: single shot US-guided interscalene brachial plexus block with 15 mL ropivacaine 0.5%.

Tests will be done to evaluate the nerve block-induced loss of sensation to ice prior to entering the operating room (OR). Diaphragmatic excursion will be evaluated using an abdominal curvilinear ultrasound probe, and will be classified as being normal, paradoxical or immobile. Normal motion is caudad movement during inspiration. Paradoxical motion is cephalad movement during inspiration.

Once in the operating room, all routine monitors are connected. Moreover, the PMD TM monitor as well as the BIS® monitor are connected to the anesthesia machine and to the patient. Both study monitors are switched on and will record their respective indices continuously for the duration of the anesthesia. General anesthesia will be induced with propofol (1-2 mg/kg IV; Pharmascience Inc, Canada), remifentanil (1 µg/kg IV bolus; Teva, Canada) and rocuronium (0.6-1 mg/kg IV; Sandoz Canada Inc). A bolus of dexamethasone 4mg IV will be administered after induction of general anesthesia.

Patients will also have received oral acetaminophen 1g and celecoxib 400 mg preoperatively. Intubation with an endotracheal tube is performed once the patient is adequately paralyzed (no responses to the TOF stimulation). All drugs are given according to the adjusted body weight of the patient. This is calculated with Robinson's formula: where TBW is total body weight and IBW is ideal body weight (21-22). Immediately after intubation, anesthesia is maintained with desflurane while targeting a BIS value between 45 and 55, and a remifentanil infusion and boluses are used for a NOL below 25. At the end of anesthesia, when the surgeon starts closing the wounds, an IV bolus of hydromorphone 7 mcg/kg of adjusted body weight is administered. The remifentanil infusion and desflurane are discontinued when dressing starts. Emergence and extubation are done in the OR. All times (start skin closure, start dressing, stop desflurane and remifentanil) will be precisely reported in the CRF.