Peripheral nerve blocks provide many advantages for patients (excellent pain control and reduction in nausea) undergoing upper and lower limb surgery however several commonly occurring complications can produce annoying but sometimes serious adverse effects. The interscalene brachial plexus block (ISBPB) is one such technique, commonly performed for shoulder surgery, but also produces paralysis of the diaphragm, Horner's syndrome and sometimes vocal cord paralysis with standard volumes of local anesthetic. This threat of these side effects limits the use of ISBPB in many patients who would particularly benefit e.g. patients with lung disease. Recently the use of ultrasound guidance is allowing practitioners to place smaller volumes of local anesthetic with much greater accuracy. This can potentially avoid anesthetizing important adjacent nerves to the target structure. If ultrasound-guided techniques with smaller volumes of local anesthetic could be demonstrated to reduce the incidence of complications without reducing effectiveness this would be very beneficial for patients.This will be the first randomized, double blind study to evaluate if an ultrasound-guided ISBPB with low volumes of local anesthetic can reduce complications for patients whilst maintaining quality of anesthesia and pain relief in the intra-operative and postoperative period.

Inclusion Criteria:

• Patients undergoing elective shoulder surgery.
• Patients aged >=18 and <=70 years
• ASA I-III
• BMI<35

Exclusion Criteria:

• Preexisting COPD
• Unstable asthma
• Psychiatric history
• Allergy to ropivacaine.
• Opioid tolerance (>30mg oral morphine or equivalent/day)