Individual duration of axillary brachial plexus block is unpredictable: A prospective double centered observational study

BACKGROUND: The duration of effect for axillary plexus block using ropivacaine is highly variable. The available literature does not offer any plausible means of predicting time of block offset for individual patients, making it difficult to give accurate information and plan postoperative analgesics. This study was designed to identify factors influencing axillary plexus block offset time. METHODS: Atotal of 92 patients participated in this prospective double centred observational study. All patients were scheduled for axillary plexus block with ropivacaine 0.75% and subsequent block duration was recorded. RESULTS: Mean time of axillary plexus block offset was 13.5 hours, with a range of 4.8 to 25.4 hours. No statistical significant differences in offset time was seen with regard to gender, age, body weight, BMI and ASA-classification. A trend for increasing duration of blocks associated with increasing age was observed. No statistically significant difference was identified in block duration between blocks performed with nerve stimulator guidance versus ultrasound guidance. Similarly, neither dose nor volume of ropivacaine 0.75% was identified as a factor influencing block duration. CONCLUSIONS: This prospective study demonstrates a large inter individual variation in time of axillary plexus block offset using ropivacaine 0.75%. The lack of association between offset time and both demographic and block performance factors, makes predictability of individual duration of axillary plexus blocks in clinical practice extremely difficult. We suggest that all patients should be made aware of such variability in duration prior to block placement.