MEV to Block the Posterior and Lateral Cords of the Infraclavicular Brachial Plexus

Minimum Effective Volume (MEV95%) of Ropivacaine 7.5 mg/ml to Block the Posterior and Lateral Cords of the Infraclavicular Brachial Plexus

The investigators have recently shown that LSIB in combination with a suprascapular and a cervical plexus block is a very good alternative for arthroscopic shoulder surgery. However, the investigators believe the total volume of local anesthetic for LSIB may be reduced. For shoulder surgery there is no need to block the medial cord and the investigators therefore hypothesize a significantly lower MEV95% by applying a selective lateral and posterior cord block

The MEV for a successful block in 50% of the participants will be determined by using the staircase up-and-down method introduced by Dixon and Massey. Logistic regression and probit transformation will be applied to estimate the MEV for a successful block in 95% of the participants.

Inclusion Criteria:

• . Inclusion criteria are American Society of Anesthesiologists (ASA) physical status I-III, age between 18 and 70 years and body mass index (BMI) between 20 and 35 kg/m2.

Exclusion Criteria:

• Exclusion criteria are pregnancy, patients with contraindications to regional anesthesia, allergy to LAs, patients taking opioids regularly due to chronic pain, use of anticoagulation drugs other than acetylsalicylic acid or dipyridamole, atrioventricular block, diabetes.