The aim of this study is to evaluate differences between ultrasound guided supraclavicular versus retroclavicular brachial plexus blocks: two similar brachial plexus nerve block techniques that differ in their needle trajectory and injection site.

To date, there has not been a study that has compared clinically the retroclavicular brachial plexus block to the supraclavicular brachial plexus block or other brachial plexus blocks. The aim of this study is to evaluate differences between ultrasound guided supraclavicular versus retroclavicular brachial plexus blocks, with primary focus on the incidence of diminished ipsilateral hemidiaphramatic excursion (ipsilateral phrenic nerve blockade). We will also evaluate differences between the two techniques in the success of producing surgical anesthesia, procedural time to perform the block (including imaging time and needling time), block onset time, ease of quality ultrasound needle visualization, and incidence of paresthesias, vascular puncture and pneumothorax. Lastly, we will observe and compare the distribution of motor and sensory blockade of the two techniques

Inclusion Criteria:

1. patients scheduled for lower arm surgery
2. patients aged 18 years or older
3. patients ASA class I-III

Exclusion Criteria:

1. Patients unable to cooperate or consent to the study
2. pre-existing neuropathy
3. significant pulmonary disease
4. contralateral phrenic nerve or diaphragmatic dysfunction
5. allergy to local anesthetics
6. infection at needle insertion site
7. history of coagulopathy
8. BMI > 40 kg/m2