Patients will be randomized to one of two groups:

1. Extrafascial injection group: Ultrasound-guided supraclavicular brachial plexus block with 2 injections of local anaesthetic, deposited at the exterior of the fascial sheath that surrounds the nerves
2. Intrafascial injection group: Ultrasound-guided supraclavicular brachial plexus block with 2 injections of local anaesthetic, deposited at the interior of the fascial sheath that surrounds the nerves

The study will be proposed to all patients undergoing formarm or hand surgery under axillary brachial plexus block. Patients will be randomized to one of two groups.

The first group - extrafascial injection group - will receive an ultrasound-guided supraclavicular brachial plexus block whereby the local anesthetic will be deposited at the exterior of the fascial sheath that surrounds the nerves.

The second group - intrafascial injection group - will receive an ultrasound-guided supraclavicular brachial plexus block whereby the local anesthetic will be deposited at the interior of the fascial sheath that surrounds the nerves.

All patients will receive the same type and amount of local anesthetic: 30 ml of a mixture of ropivacaine 0.5 % + mepivacaine 1 %.

The primary outcome is the rate of hemidiaphragmatic paresis 30 minutes after the block procedure, assessed with ultrasound. Secondary outcomes are: rate of hemidiaphragmatic paresis 2 hours after surgery, assessed with ultrasound, bedside spirometry before the supraclavicular block, 30 minutes after the block and 2 hours after surgery, rate of successful block 30 minutes after the block , duration of sensory and motor block, pain scores at rest and on movement at 24 h postoperatively, cumulative postoperative opioid consumption at 24 hours postoperatively and patient satisfaction with overall anesthetic management.

These outcomes are further defined in the section below.

Inclusion Criteria:

• Patients undergoing forearm or hand surgery under locoregional anesthesia
• ASA physical status I-III

Exclusion Criteria:

• Patient refusal
• ASA physical status IV
• Severe pre-existing lung disease
• Patient unwilling or unable to perform incentive spirometry
• Local anesthetic intolerance or allergy
• Neurological deficit or neuropathy of the arm
• Coagulopathy contraindicating locoregional anesthesia
• Malignancy or infection in the area above the clavicle
• Pregnancy
• Inability to understand the informed consent

no sharing of any IPD

The participants and all care providers will be blinded to the patient assignment.