Despite their reliability and efficacy for shoulder surgery analgesia, above clavicle brachial plexus blocks are related with phrenic nerve palsy and diaphragm paralysis that may not be tolerated in patients with chronic pulmonary disease.

This RCT will compare the classic Interscalene block with combined infraclavicular block plus suprascapular nerve block in patients going for arthroscopic shoulder surgery.

Main outcome is static pain in the recovery room measured with NRS. Secondary outcomes are pain at 12 and 24 hrs and incidence of diaphragmatic paralysis.

PATIENT RECRUITMENT

With the approval of the Ethics Committee of Hospital Clinico Universidad de Chile, 40 patients undergoing arthroscopic shoulder surgery will be recruited. Enrollment will be carried out by an investigator not involved in patient care. Patients' confidentiality will be protected.

STUDY PROTOCOL: GENERAL

All blocks will be performed by one of the coauthors and conducted preoperatively in an induction room. Sedation (2 mg midazolam and 50 μg fentanyl) will be provided for patient comfort.

STUDY PROTOCOL: PERFORMANCE OF THE BLOCK

Both study groups will receive an ultrasound-guided superficial cervical plexus block.

In the ICB-SSB group, suprascapular nerve blocks will be carried out using a previously described technique. For infraclavicular brachial plexus blocks, 20 mL of levobupivacaine 0.25% with epinephrine 5 µg/mL will be injected dorsal to the axillary artery, medial to the coracoid process.

In the ISB group, block will carried out using a previously described technique: 20 mL of levobupivacaine 0.25% with epinephrine 5 µg/mL will be deposited under the prevertebral fascial between the C5 and C6 roots.

STUDY PROTOCOL: GENERAL ANESTHESIA

All patients will undergo standardized general anesthesia

STUDY PROTOCOL: POSTOPERATIVE ANALGESIA

In the Recovery Room, all patients will receive acetaminophen (usual dose…) and ketoprofen (usual dose…) as well as patient controlled analgesia (morphine bolus = 1 mg; lockout interval = 8 minutes). On the surgical ward, all subjects will continue to receive acetaminophen (usual dise…), celecoxib (usual dose…) as well and patient controlled analgesia (morphine bolus = 1 mg IV; lockout interval = 8 minutes).

STUDY PROTOCOL: OUTCOME MEASUREMENTS

The primary outcome will be the pain score in the PACU at 30 30 minutes using a sensorimotor composite scale:

Performance time, sensorimotorSensory function, Onset time

The blinded investigator will also assess the presence of hemidiaphragmatic block at 30 minutes. A 2-6 MHz curvilinear US probe (Sonosite M-Turbo, SonoSite Inc, Bothell, WA, USA) and the M-mode will be employed in all subjects; the liver and spleen will serve as acoustic windows on the right and left side, respectively. Patients will be scanned along the anterior axillary line and the US probe, angled cranially

POTENTIAL BENEFITS OF THE STUDY This study will allow us to determine if ICB-SSB constitutes a viable alternative to ISB.

POTENTIAL SIDE EFFECTS OF THE STUDY Participation in this protocol will not put patients at higher risk for complications since ISB and ICB-SSB are commonly used to provide analgesia for shoulder surgery

Inclusion Criteria:

• age between 18 and 75 years
• American Society of Anesthesiologists classification 1-3
• body mass index between 20 and 30

Exclusion Criteria:

• adults who are unable to give their own consent
• pre-existing neuropathy (assessed by history and physical examination)
• coagulopathy (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. platelets ≤ 100, International Normalized Ratio ≥ 1.4 or prothrombin time ≥ 50)
• obstructive or restrictive pulmonary disease (assessed by history and physical examination)
• renal failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. creatinine ≥ 100)
• hepatic failure (assessed by history and physical examination and, if deemed clinically necessary, by blood work up i.e. transaminases ≥ 100)
• allergy to local anesthetics (LAs)
• pregnancy
• prior surgery in the neck, infraclavicular region or suprascapular fossa
• chronic pain syndromes requiring opioid intake at home