In this trial, the objective is to compare single- and double-injection ultrasound-guided costoclavicular blocks. The rationale behind this idea is that a second local anesthetic injection, inside the costoclavicular space, may compensate for the dynamic cord dispersion seen with the single-injection technique. Thus the research hypothesis is that, compared to its single-injection counterpart, a double injection costoclavicular block will result in a shorter onset time.

The costoclavicular block (CCB) constitutes a relatively novel technique for infraclavicular brachial plexus blockade, whereby local anesthetics (LAs) are injected inside the costoclavicular space. In this location, the 3 cords of the brachial plexus are very tightly clustered together; this topography would theoretically result in a very swift brachial plexus block Unfortunately, in two recent trials comparing CCB and conventional infraclavicular brachial plexus block, the authors were unable to detect differences in success rate, onset times and LA requirement between the 2 methods. It could be speculated that the explanation resides in dynamic cord dispersion. With CCB, the initial needle target lies in the middle of the 3 cords of the brachial plexus. However, with LA injection, the cords can quickly migrate away from each other. Thus, the anatomical benefits conveyed by the initial compact topography may be lost.

In this trial, the objective is to compare single- and double-injection ultrasound-guided costoclavicular blocks. The rationale behind this idea is that a second local anesthetic injection, inside the costoclavicular space, may compensate for the dynamic cord dispersion seen with the single-injection technique. Thus the research hypothesis is that, compared to its single-injection counterpart, a double injection costoclavicular block will result in a shorter onset time.

Inclusion Criteria:

• age between 18 and 75 years
• American Society of Anesthesiologists classification 1-3
• body mass index between 18 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 partial thromboplastin time ≥ 50)
• 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 anesthetic
• pregnancy
• prior surgery in the infraclavicular costoclavicular region
• chronic pain syndromes requiring opioid intake at home

Participants will not be allowed to see the ultrasound screen. Outcome assessors will not be present during the performance of the block.