Interscalene brachial plexus block is known as the gold standard for analgesia after shoulder surgery, but limits the use of ipsilateral phrenic nerve paralysis. Recently, interest in potential diaphragm-sparing alternative blocks has increased for patients undergoing shoulder surgery.Two of these blocks are upper trunk block (UTB) and costoclavicular brachial plexus (CCBPB) block. This randomized controlled trial will compare ultrasound-guided UTB and CCBPB in patients undergoing arthroscopic shoulder surgery.

The main outcome is pain intensity score at 30 minutes after arrival in the post anesthesia care unit (PACU) as measured by a numerical rating scale (NRS) from 0 to 10. The investigators research hypothesis is that UTB and CCBPB will result in equivalent postoperative analgesia at 30 minutes in the PACU.

Inclusion Criteria:

1. American Association of Anesthesiologists (ASA) physical status I - III
2. BMI 20 to 35 kg / m2
3. Patients scheduled for elective arthroscopic shoulder surgery

Exclusion Criteria:

1. Patients who refuse to participate in the study,
2. Pre-existing (obstructive or restrictive) lung disease,
3. Coagulopathy,
4. Sepsis,
5. Hepatic or renal insufficiency,
6. Pregnancy
7. Allergy to local anesthetic drugs,
8. Chronic pain condition requiring opioid intake at home,
9. Surgery in the neck or infraclavicular region
10. BMI above 40.
11. History of psychiatric diseases needing treatment.
12. Failure of nerve block performed in the preoperative block room
13. Substance abuse history