Radiological evaluation of the spread of different local anesthetic volumes during posterior brachial plexus block.

Local anesthetic spread during interscalenic block has been thoroughly studied, however there are few studies on posterior block. This study aimed at evaluating the spread of different local anesthetic volumes during posterior brachial plexus block using contrasted X-rays. Participated in this study 16 patients submitted to posterior brachial plexus block, 15 of whom were randomly divided in three groups of five patients: Group 1: 20 mL; Group 2: 30 mL.; Group 3 40 mL. The volume of 10 mL was studied in one patient submitted to continuous posterior brachial plexus block. All patients received 0.375% ropivacaine associated to radio-opaque solution. X-rays of the cervical region were obtained immediately after blockade that were evaluated by thermal sensitivity using cotton soaked in alcohol 30 minutes after being performed and in the PACU. Radiological and clinical behavior of posterior brachial plexus block is very similar to Winnies technique (interscalenic). There is always involvement of cervical plexus and of higher brachial plexus roots (C5-C7). This study has shown that local anesthetic spread during posterior brachial plexus block is seen primarily in shoulder innervating roots.