Postoperative analgesia for shoulder surgery is typically achieved by providing an interscalene brachial plexus block. However, a very common side effect of this block is hemi-diaphragmatic paralysis, a state which may not be tolerated in patients with pulmonary conditions such as COPD. Recently, clinicians have explored new ways to provide satisfactory analgesia while minimizing the pulmonary side effects of the interscalene nerve block. One of these solutions might be to offer the patient a suprascapular nerve block combined to a costoclavicular block. Since these blocks are performed lower in the neck or under the clavicle, the phrenic nerve is less likely to be blocked. Thus, fewer respiratory side effects have been reported when using such blocks. This prospective observational study will evaluate the patient response to surgical stimuli and the opioid requirements intraoperatively in patients undergoing shoulder arthroscopies with either a supraclavicular and costoclavicular blocks or an interscalene block.

Study Design: Prospective, randomized open label non-inferiority trial. Subject Population: Adults scheduled to undergo elective shoulder arthroscopy Sample Size: 50 patients Study Duration: Starts February 2020 - Ends February 2021 - Interim analysis at 30 patients Study Center: Assuit university hospital

The main hypothesis of this study is that the suprascapular block combined with a costoclavicular block is not inferior to the interscalene brachial plexus block in terms of postoperative analgesia. Inverstigators postulate that postoperative pain score will not differ significantly in patients who receive either block.

secondary objectives will consist in looking at the differences in intraoperative anesthetic consumption, postoperative opioid consumption, arm motor block, diaphragmatic paresis, patient satisfaction and time for readiness to discharge from PACU. investigators 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 costoclavicular 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. patients will be approached and the whole study procedures will be explained extensively. Interested patients will be invited to sign the consent form .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 bupivacaine 0.5%, then single shot US-guided costoclavicular block with 10 ml bupivacaine 0.5%.
• Group B: single shot US-guided interscalene brachial plexus block with 15 mL bupivacaine 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.. 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), fentanil (1 µg/kg IV bolus) and cis-atracium (0.1-0.2 mg/kg IV; ). A bolus of dexamethasone 4mg IV will be administered after induction of general anesthesia.

Patients will also have received oral acetaminophen 1g preoperatively. Intubation with an endotracheal tube is performed once the patient is adequately paralyzed . 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 isoflurane . At the end of anesthesia, Emergence and extubation are done in the OR. All times (start skin closure, start dressing, stop isoflurane) will be precisely reported in the CRF.

Inclusion Criteria:

ASA status 1,2,3.

• Age 18 years or older
• Elective shoulder arthroscopic surgery under general anesthesia and nerve block performed preoperatively

Exclusion Criteria:

• Serious cardiac arrhythmias (including atrial fibrillation) or unstable coronary artery disease.
• Coagulation disorders.
• Patient refusal.
• Anatomical disorders and/or neuropathic disease.
• BMI above 40.
• History of substance abuse.
• Chronic use of psychotropic and/or opioid.
• History of psychiatric diseases needing treatment.
• Contraindications to nerve block for shoulder surgery.
• Allergy to fentanil or any drug in the study protocol.
• Failure of nerve block