Minimum effective volume of ropivacaine 7.5 mg/ml for an ultrasound‐guided infraclavicular brachial plexus block

Background Ultrasound guidance has been shown to reduce the minimum effective volume ( MEV ) of local anaesthetics for several peripheral nerve blocks. Although the lateral sagittal infraclavicular block ( LSIB ) is a well‐established anaesthesia method, MEV for this technique has not been established. Our aim with this study was to determine the MEV using ropivacaine 7.5 mg/ml for the LSIB method. Methods Twenty‐five adult American Society of Anesthesiologists physical status I ‐ II patients scheduled for hand surgery received an ultrasound‐guided LSIB with ropivacaine 7.5 mg/ml. A successful block was defined as anaesthesia or analgesia for all five sensory nerves distal to the elbow, 30 min after local anaesthetic injection. The MEV for a successful block in 50% of the patients was determined by using the staircase up‐and‐down method introduced by D ixon and M assey. Logistic regression and probit transformation were applied to estimate the MEV for a successful block in 95% of the patients.Results The patients received ropivacaine 7.5 mg/ml volumes in the range of 12.5–30 ml. The MEVs in 50% and 95% of the patients were 19 ml [95% confidence interval ( CI ), 14–27] and 31 ml (95% CI , 18–45), respectively. Conclusions For surgery distal to the elbow, the MEV in 95% of patients for an ultrasound‐guided LSIB with ropivacaine 7.5 mg/ml was estimated to be 31 ml (95% CI , 18–45 ml). Further studies should determine the factors that influence the volume of local anaesthetic required for a successful infraclavicular block.