Minimum Effective Local Anesthetic Volume for Ultrasound Guided Superior Trunk Block

Shoulder arthroscopic surgery is one of the most commonly performed procedures worldwide, and associated with significant postoperative pain. Currently, such surgery is performed either under general anaesthesia or under Interscalene brachial plexus block (ISBPB), which is a regional anaesthesia technique. However, ISBPB is associated with the highest incidence of hemi-diaphragmatic palsy of the operative side. Since majority of the innervation to the shoulder arises from or passes through the superior trunk of the brachial plexus, superior trunk block has been shown to have lesser impact on the phrenic nerve and it has been gaining popularity worldwide. Ultrasound is widely used for brachial plexus block and current evidence indicates that it is feasible to accurately identify majority of the main components of the brachial plexus above the clavicle, including the three trunks (superior, middle, and inferior trunks). However, there are no data describing an optimal volume of local anaesthetic for superior trunk block. The aim of this study is to identify the minimum effective dosage of a commonly used local anaesthetic drug "levobupivacaine" required to produce an effective ultrasound guided (USG) superior trunk block (STB) in at least 90% of patients for shoulder arthroscopic surgeries.